10mm .40 S&W
10mm Auto (left), .40 S&W (right) (Image: Jeremy S. for TTAG)
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First there was 10mm Auto. The FBI chose a watered-down loading — a 180 grain bullet at 975 fps instead of more like 1,300 fps — and a large-frame Smith & Wesson pistol through which to shoot it. By the time the contract went through, Tom Campbell, a S&W employee, had realized that the powder capacity of the 10mm’s 25.2 mm-long case simply wasn’t necessary to achieve this same velocity. And that’s how the .40 S&W with its 21.6 mm-long case was born.

For all intents and purposes .40 S&W is really “10mm Short & Weak.” Brief history complete, let’s skip to the part where I’ve chosen to shoot it regularly through stock 10mm GLOCKs.

First, yes, the disclaimer: Don’t do this. It isn’t okay to shoot a caliber in a firearm that wasn’t designed for that caliber. I’m going to tell you why I do it and why I actually believe it’s safer to shoot .40 S&W in a 10mm GLOCK…safer than either 10mm in a 10mm or .40 in a .40. Dut that doesn’t mean I’m suggesting that you do it. So don’t.

Second, this all pertains to a GLOCK. Shooting .40 S&W in many or most other 10mm pistols sans conversion barrel can be problematic or unsafe.


A competitive shooter I knew in California shot a GLOCK 20 in Production class. However, he shot .40 S&W from it. No need to shoot the stronger and significantly more expensive 10mm just to make Major power factor, yet he’s an extremely tall guy with gigantic hands and the G20 frame fit him better.

GLOCK 20 10mm
Ryan Finn for TTAG

Additionally, the extra mass of the gun made it shoot that much softer and flatter. He shot about 5,000 rounds per year, and was in his 4th year with the same G20 when I met him. Before the G20, he was shooting a GLOCK 22 until he encountered another bloke who was running .40 S&W through his G20 and claimed to have put many thousands of rounds through it without a hitch.

Confirming complete and total reliability through his G20, I was also surprised to see that once the barrel was cleaned, it was entirely indistinguishable from any other GLOCK barrel. Finish wear on the outside attested to the round count, but the inside was pristine.

Digging into this further, I found that it’s actually a fairly common practice among the GLOCK set and I started doing it myself. I got my G20SF for bear defense while Huckleberry picking and, yes, to shoot full-power 10mm through it. But when I’m practicing, plinking, and target shooting — or testing out new GLOCK sights like these that are on my G20 right now — I’m usually shooting the less expensive .40 S&W.

No, I do not have a conversion barrel and I don’t feel any need whatsoever to buy one. I also had a Gen4 G29 — the sub-compact 10mm — for about a year and shot a couple hundred .40’s through that bad boy without a hitch.

Why It Works

10mm Auto ammunition
Josh Wayner for TTAG

Many people believe the extractor in a pistol snaps over the rim of the cartridge, but that’s not actually how it happens. As the bottom of the breech face strips the round out of the magazine and the feed ramp lifts the round upwards, the base of the cartridge moves up the breech face, sliding underneath the extractor.

Feeding a .40 S&W round from a 10mm magazine in a 10mm GLOCK pistol follows this process just as it should. Since the .40 S&W brass is 3.6mm shorter, its forward progress isn’t stopped by the end of the 10mm chamber (it doesn’t headspace on the case mouth). Instead, the extractor hangs onto it and keeps it up against the breech face.

Obviously the .40 caliber bullet has a few more millimeters of free bore travel before it contacts rifling than a 10mm round would, but this is far from unique in the firearms world.

Every revolver necessitates bullet travel before rifling is encountered, especially in cases where you’re shooting a shorter, less-powerful version of the cartridge the revolver is designed for. Think .38 Special out of a .357 Magnum or the various .32 cartridges from a .327 Federal Magnum, or, heck, a .45 LC out of a 3″-chambered Taurus Judge. Or a .22 Short out of a .22 LR.

.40 S&W ammunition
Josh Wayner for TTAG

The .40 S&W round has identical exterior dimensions to 10mm, uses the exact same bullets, has the same rim dimensions, etc. It uses a small pistol primer instead of a large one, is rated for 35,000 PSI instead of the 37,500 PSI of the 10mm, and is obviously a bit shorter in case length and overall loaded cartridge length.

Other than “headspacing off the extractor” instead of the case mouth, everything else is functionally the same as 10mm as far as a GLOCK is concerned.

As a 10mm GLOCK is tuned from the factory to reliably run FBI-spec 10mm, it will run .40 S&W as, again, .40 was designed to be ballistically identical to FBI 10mm. With the exception of brands like Underwood, Buffalo Bore, DoubleTap, and a couple of the big names, much of the “10mm” ammo on the market is loaded dang close to a given brand’s .40 cal.

For instance, Federal American Eagle and Federal Hydra-Shok have stated velocities of 1,000 fps for 180 grn .40 and 1,030 fps for 180 grn 10mm. In fact, even when I install my 21-lb (a few lbs stiffer than factory) Lone Wolf recoil spring, it still cycles .40 with complete reliability.


As mentioned, I believe shooting .40 S&W in a 10mm GLOCK is not only safe, but is actually safer than shooting 10mm in a 10mm GLOCK or .40 in a .40 GLOCK.

Here’s why I don’t hesitate to do it:

1) Headspace “Kabooms” can occur due to excessive headspace — the distance between the breech face and the end of the chamber (in this case the lip on which the case mouth stops) — caused by the cartridge protruding too far out the back (ejection port side) of the chamber.

With fairly generous chamber diameters and less-than-complete case support — the “GLOCK Smile” appears on .40 S&W and 10mm cases when shot through the correct GLOCK models due to limited case support above the feed ramp — it doesn’t take very much excess headspace to cause a case rupture.

Since these rimless cartridges are designed to headspace off the mouth of the case when it hits the front of the chamber, a piece of brass that’s slightly too long, a bullet that isn’t seated deeply enough, heavy chamber fouling, and/or a slide that doesn’t quite go fully into battery can and does cause this dangerous scenario. Both 10mm and .40 S&W GLOCKs are relatively notorious for case blowouts and this is a big reason why.

Conversely, when the shorter .40 S&W cartridge is chambered in the 10mm chamber, there’s effectively no physical way for it to be anything less than completely chambered. Even out of spec, too-long brass with a shallow-seated bullet is going to have room in the chamber and the slide is going to be completely in battery, as far forwards as it’s capable of going. The least headspace possible. Every time.

In fact, this can be seen immediately if one happens to have both a .40 and a 10mm GLOCK handy. Forty caliber brass shot out of the .40 will show the GLOCK Smile (as does 10mm out of a 10mm). Forty caliber brass shot out of the 10mm will not.

There is no longer any GLOCK case bulge, or at least it’s greatly reduced. The case is more fully chambered and better supported. If you reload, you’ll be happy to know that fired .40 cases look and measure better when shot through a 10mm barrel (case length changes by no more or less than normal, and rims are normal).

2) Overbuilt A 10mm GLOCK pistol has a heavier and thicker slide, thicker chamber and barrel walls, a stronger recoil spring, and a larger locking block than a .40 GLOCK. In the event of a .40 S&W round that’s over pressure due to excessive powder, a bullet that is seated too deeply, etc, the pistol is more likely to shrug it off or at least more likely to suffer less damage.

3) Firing Pin This is what makes this uniquely safe in a GLOCK, but a bit sketchy in many other firearms. The big, rectangular slab of a GLOCK firing pin (striker) comes to a hard stop without projecting very far from the breech face. Should the extractor miss the case rim for some reason or slip off of it — neither of which it ever freakin’ does, by the way — the .40 S&W round would plunk down into the chamber, held forwards off of the breech face by the extractor far enough that the firing pin is physically incapable of contacting the primer.

This isn’t the case in some 1911s and other guns. While this still actually isn’t likely to cause a serious safety problem, it isn’t ideal for the case to slam backwards into the breech face and it can lead to pierced primers and worn out or broken extractors, and maybe failures to eject.

The unlikely safety issue would be separation of the case rim/base from the rest of the casing. Again, it won’t happen in a GLOCK because the extractor is either holding the cartridge against the breech face and all is well, or it isn’t and the firing pin can’t reach the primer in the first place.

Primer strikes on .40 S&W cases shot through 10mm GLOCKs look indistinguishable from those shot through .40 S&W GLOCKs. This isn’t usually the case in other pistols with normally-shaped firing pins, which tend to exhibit excessively-deep primer strikes and sometimes pierced primers.

4) Extractor The GLOCK extractor is pretty wide and beefy. A concern for extractor lifespan is probably the #1 “don’t do this because…” thing I hear on this .40/10mm topic after safety concerns are dismissed.

I think the theoretical stress on the extractor from having to stop the round from plunking into the chamber is exaggerated. That forward pull is just nothing compared to how hard it sometimes has to tug on cases to pull them out of the chamber. I don’t deny that the extractor is doing work on the chambering stroke when it usually doesn’t, but I see it as much lighter work than its normal duty and, as they say, the proof is in the pudding.

The proof is in the countless G20s with multiple thousands of rounds of .40 through them with no extractor breakages or issues of any sort. In theory, practice is the same as theory, but in practice it rarely is. It’s also like an $18 part, and it’s not like they don’t sometimes break in by-the-book usage. I don’t think this increases the chances.

Additionally, it’s sometimes the case that the correct cartridge in the correct gun doesn’t headspace on the case mouth anyway. With brass that’s only a little bit on the short side — often even within SAAMI-approved tolerances — it doesn’t contact the end of the chamber. Short is okay, long is bad (see #1 above).

As for any gap between the breech face and the cartridge base, some gap there is really a non-issue on a pistol cartridge and all revolvers have some gap there (between case base and recoil shield) so the cylinder can rotate. The GLOCK extractor pins the round against the breech face under spring tension. The extractor isn’t just hovering there over the rim, it’s actually clamped down on it. There is no gap, and the round is held solidly in place:

Jeremy S. for TTAG


Note extractor is moved outwards by the case rim. (Jeremy S. for TTAG)

5) Chamber / throat erosion Folks are convinced that the shorter, .40 cal brass means the gasses and bullet will impact the chamber lip and wear it out. Again, I understand this intuitively, but it doesn’t pan out in practice.

The gasses from the pistol cartridge just aren’t hot enough and high-pressure enough to begin to wear away the steel for many, many tens of thousands of rounds. Again, some of the time the 10mm brass isn’t going to seal against the chamber lip anyway.

As the full diameter of either the 10mm or .40 caliber projectile is behind the chamber lip, they both have the ability to touch it. The copper and lead isn’t hard enough to erode that cold hammer forged steel except for, again, after many tens of thousands of rounds exactly as it takes that sort of time for the rifling to get worn down in a standard pistol barrel.

I’ve now seen multiple factory GLOCK barrels with multiple tens of thousands of rounds of .40 S&W through them and, when clean, no GLOCK armorer or gunsmith on the planet could tell by looking at the chamber lip or the bore that .40 was fired through it instead of 10mm.

On The Range

It’s completely reliable. I have never suffered a stoppage of any sort, with all possible combinations of factory barrel, factory recoil spring, Lone Wolf 6.6″ 10mm barrel, and Lone Wolf 21-pound recoil spring. Nor was there a hitch in the couple hundred rounds fired through the unmodified Gen4 G29 that I had.

The guy that piqued my interest in this had never suffered a single .40-in-a-10mm-related stoppage — he encountered a few truly dud primers — and during the competition season in which we were in contact he was working on rounds ~15,000 to ~20,000.

It’s not quite as accurate as 10mm in a 10mm barrel or .40 in a .40 barrel. That little bit of free bore has a very minor, detrimental effect on accuracy. Obviously it isn’t enough to negatively affect USPSA scores. The gun will still shoot groups that anyone would call typical for a GLOCK. However, I did take the time to do various testing around this and group sizes are just slightly larger than when shooting either caliber through its correct barrel.

The Legitimate Safety Concern

As the .40 S&W brass is shorter, shooting it will cause a bit more carbon fouling than usual in the front of the chamber. It is advisable to clean the chamber before switching back to 10mm.

As we’ve already discussed, excessive headspace can lead to a kaboom — especially with a GLOCK-brand GLOCK barrel — and one cause of excessive headspace can be fouling that prevents a round from fully chambering.

It could take a thousand rounds of .40 S&W through a 10mm GLOCK before fouling is such that it’s even a concern for switching back to 10mm, but as there are a lot of variables that can affect the rate and type of fouling there’s no way I’d throw out a suggested round count.

Default should be cleaning, inspecting should be mandatory.


GLOCK 20 10mm G20

I expect that half of the comments will be folks talking about how stupid this is, how stupid I am for doing it, and suggesting all sorts of theories as to why that is. Again, this is just one man’s experience and opinion.

Don’t do it if you don’t want to (don’t do it if you do want to). As much as I appreciate hearing theories from folks who haven’t done it, haven’t fully thought it through, dismiss it outright because it’s “wrong,” or otherwise intuit or feel various reasons as to why it’ll break your gun and explode in your face, etc., they’re just theories. In practice, this works on all levels.

Again, I’m not suggesting anybody actually do this. You should probably also never shoot .223 in your 5.56 chamber, 7.62×51 in your .308 chamber, 2¾” shells in your 3″ chamber, .22 Short in your .22 LR chamber, etc., etc., etc., ad nauseam. (Yes, I realize these all headspace off the shoulder or rim.)

Random, Unverified “Historical” Note

The verifiable part of this history is that the Soviet military specifically designed and required that its ammunition was incompatible with NATO firearms, meaning no captured ammo could be used against them. The sketchy part of the history is that this doesn’t mean Soviet firearms weren’t made to also run on NATO (or NATO-country) ammunition.

Many folks claim that at least the Makarov, which was chambered in 9x18mm Makarov, was designed to reliably and safely cycle .380 ACP (9x17mm) and can also safely fire 9×19 (9mm Luger).

The larger diameter — 0.365″ vs. 0.355″ — a Makarov bullet can’t be chambered in a .380 or in a 9mm, but the .380 round chambers just fine in a Makarov pistol. While .380 will actually feed from the Mak magazine, fire, and eject reliably, 9×19 has to be dropped into the chamber one at a time. It also exhibits excessive headspace, as you’d expect, but likely thanks to how much gas and pressure blows by the too-small projectile (it doesn’t seal in the bore), it doesn’t blow out cases and doesn’t seem to beat up the pistol.

While there are myriad YouTube videos and forum posts confirming the reliability from .380 and successful function of 9mm (even on aluminum-framed, cheap-o, reproduction Makarovs), it’s probably best left for SHTF use only as either of these instances are more “extreme” than running .40 cal in a 10mm due to significantly larger differences between the rounds vs. the intended cartridge.


[This post was originally published in 2015.]

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  1. there is none. the ATF handles these issues, including the 5.45 x 39 ammo issue. a court just ruled that the ammo is illegal. but the group that brought the lawsuit really made a poor case. just based on the ATF rule that a round has to be .22 cal or larger and capable of armor piercing, would have won the case. a 5.45 is smaller than .22 cal.

    the other thing, there is not a deterministic definition of armor piercing, type of armor, velocity, mass, nothing to actually measure (well, .22 cal is measurable). the 5.45 debacle was base on the rounds ability to be fired from some type of hand gun (you could design a .50 BMG pistol), that was not specified by any brand. a short bbl version of this 5.45 firearm, would probably not actually yield the velocities need to achieve armor piercing.

  2. Good article I had a g20 I loved it but I had to sell it after a layoff 3 months no work. I love the 10mm and now that I have the tools to reload I want another one.

  3. “Don’t do this thing I’m about to tell you all about doing.” Seriously? What are we, three years old? If you genuinely believe you need legal cover for writing and publishing this, then maybe use some common sense and don’t write and publish it.

    OR (and here’s a really wacky idea) assume your readers are adults who can make decisions for themselves. The disingenuous disclaimer followed by detailed instructions and analysis is just patronizing.

    As for shooting the wrong ammo out of any firearm: I know you can make it work in some cases. Don’t expect me to sympathize or pay for your health care when it doesn’t work out in all cases.

    • Exactly what I was going to say. Throughout the entire article, all I could think of was “okay everyone, I know what you’re going to say, so to totally CYA myself and not risk any lawsuits by anyone who does this and somehow injures himself like an idiot, PLEASE DON’T DO THIS. Otherwise, I’m going to say totally do it because it’s better and safer than what Glock tells you to do.”

      Might be true (I’ve shot both .40 and 10mm and understand the mechanics of the author’s argument), but still funny.

      • He did this because he obviously knows how the Internet know it all’s operate. If you do not understand why he made these disclosures say’s something about your lack of knowledge about the internet, gun forums etc.
        Great informative article! Thanks
        Sorry you have to put up with the Trolls.

      The Smith & Wesson Model 610 10MM is available in two barrel lengths in the stainless steel large N-Frame revolver. The model 610 is ideally suited for personal protection or handgun hunting with the popular 10MM auto cartridge.

      3 Moon Clips Included
      Chambered for 10mm AUTO – will also fire 40 S&W

      Availability subject to applicable federal, state and local laws, regulations, and ordinances.

      • I have it in the 6” barrel what a fun gun the shoot. But realistically who can afford 10MM ammo for a day at the range? I take 1 box of real 10MM and several boxes of 40 and i have a great day.

  4. Im not going to tell you to do this but I do it all the time.
    I know of plenty of Glock 20 owners who do this. As Im not a Glock boy. Ive been doing the following.
    I shoot 40S&W out of my 10mm RIA 1911 Commander ALL the time.
    I have for 1000s of rounds with zero issues.
    Yes I know the 40 is being held in by the extractor and its not head spaced correctly.
    But it works and has for a few 1000 rounds so far.
    With no damage to the gun or barrel or even a single bulged cartridge.
    End of story works for me might not be safe or right for you or your gun..

  5. .38 Super accuracy was plagued by inconsistent headspacing until the chamber was redesigned to headspace on the case mouth like other auto calibers. Since there seem to be differences other than length between .40 and 10 mm chambers, I’m surprised no one has designed a 10 mm barrel that headspaces a .40 cartridge on the case mouth.

    • You’re kidding, right? That defines a .40 S&W, barrel, a 10mm would stop when its case mouth hit that point, ie would not chamber, just as a .357 round going into a .38 Spl cylinder.

    • I’ve thought about this and I’m not entirely convinced it’s true. Yes at one time long ago, stock Colt .38 Super pistols weren’t very accurate and yes new barrels that headspace on the case mouth solved the problem. But those barrels were also match barrels made by companies like Bar-Sto that were overall a better barrel with a tighter lock up.

      I’ve seen people fire full magazines of 9mm out of a .40 while wondering why they had to hand cycle the slide without a miss fire, so I don’t think a .38 Super barrel that head spaces on the rim would have inconsistent ignition either.

      If I had to guess it was a combination of a higher quality barrel and different dimensions in the chamber throat between the stock Colt and aftermarket barrels that caused the accuracy difference.

  6. As noted in the article any fouling build up by using .40 s&W in the longer 10mm chamber could build up more quickly than expected. Failure to clean it all out could result in the 10mm round not fully chambering and everyone should know Glocks inferior lock up design can and will let the striker hit the primer enough to set it off when the slide is not fully forward. Doubt my word? Then take an empty case and prime it and then let the slide run almost but not fully forward and pull the trigger. You will see a dent in the primer, albeit a small dent but a sensitive primer can then detonate. And you can get hurt doing this so I just warned you if you try it. Wear a face shield and welders elbow length gloves.

    A far better idea would be just to hand load the 10mm down with less powder, you will get better accuracy with the full length 10mm case and no chance of blowing yourself up either.

    Of course installing a .40 S&W barrel would be another option. I ask you what is your eyesight worth to you?

  7. Jeremy, cool article, thanks. I gotta comment on your description of soviet bloc weapons and the ammo exchangeability, since it finally showed me where certain rumors came from. When I was in Vietnam, ’71-’72, many people “KNEW” that AK47s could fire M16 ammo, but M16s could not fire AK47 ammo. I had a roommate who *insisted* this was true, even after I pointed out that one was .30 cal and the other was a .22, all I got was “I don’t care, it’s the truth”. So, since I had some handy, I pulled out an AK mag and stripped a 7.62×39 out of it, then stripped a 5.56 round out of one of my M16 mags, and set them on the table in front of him and pointed out the differences in case length, case diameter, and shoulder location, indeed overall size, asking how that could POSSIBLY be true, and still got the same reply, “I don’t care, ” etc. I suppose I shouldn’t have been shocked, I could not convince people I knew in the States that the M16 bullet was not triangular. Really! Even after I told them I had carried a loaded M16 around for a year, loaded and unloaded it many times, they still would not believe me that it just looked like a bullet. The same story about the US .50 cal vs the soviet .51 cal, but I don’t know whether that one was true or not, never saw the ammo together.

    • I used to hear that latrine talk about the soviet ammo. We had a .50 cal so they had a .51. The word was that they could use our ammo in their weapons but not the other way round. Ours was the 81mm mortar. Theirs the 82.

      Trying to convince folks that ‘just knew’ that there was a lot more involved than just bore diameter was a lost cause.

    • Larry, when I was in we were told 7.62X39 could be fired in 7.62X51. Not 5.56. This by senior NCO range officers. When I called bullshit I was shouted down by my fellow soldiers. Same with our .50 BMG round in the Soviet 14mm. Or vice versa. Few rifle calibers are interchangeable. The .458 Win Mag fired in a .450 Lott notwithstanding. Fire forms the brass. Working off memory so I could be wrong.

    • I have a 5.56 here that I did shoot through an AK 7.62, yes the 5.6 will shoot in an AK. How can that be, the 5.6 case forms a little back from the shoulder and the neck forms to the chamber. The AK’s extractor holds the 5.6 secure enough to set off the primer, amazingly the bolt head of the AK centers the 5.5 case. However it’s a one shot deal as the case sticks in the chamber. It’s not safe but ,many cartridges can be fired in a different chamberings. I’d send pic of the 5.6 shot in an AK but don’t know how

      • I hear ya, Possum, but what do ya suppose the muzzle velocity was? Around 20 fps? I mean, not only are the gasses just flowing right past the bullet, but the case is not even contained in the chamber!

        • I wouldn’t stand in front of it. The bullet did go through one side of a refrigerator.

    • Yeah, same thing with the Commie 82mm mortar v. our 81mm mortars. Too busy fighting to ever get the chance to test out that theory and never picked up a serviceable enemy 82 off a battlefield area, but we did get enough extra range out of adding an experimental extra five pack of propellant to our max chargeed 4.2 inch mortars which painfully perplexed the Viet Cong who thought they were the monkey’s ass because they had our max ranges down just exactly down to be able to comfortably stay a couple hundred meters out of our max saturation range…until they weren’t!

  8. The Article is very interesting. I am one of many loyal .40S&W users. We get crap from the lemmings that went “back” to 9mm because of the FBI tests but they don’t use that specific magic cartridge. We also get crap from the 10mm folks for our .40 “short and weak”. Your mention of most common 10mm (not on steroids) ammo velocities being close enough to 40S&W (30fps+-) is an eye opener: seems the “weak” lable has wider application than 10 mm folks think. Keeping it in perspective: there’s about the same velicoty difference between a five and six inch barrels using 10mm Fed Hydrashok 180gr.
    Thanks “for the ammo”. Lol

    • Will, agree with you completely. I’ll shoot .38 Spl in .357 Mag. .44 Spl in .44 Mag. Never a lesser cartridge in an auto. As far as the FBI, and others, going “back” to the 9mm. That’s the bean counters. Not the gunfighters. 9mm is less expensive. 9mm has to expand to get where .40 S&W starts. The FBI is probably going to relearn a hard lesson they already learned in Miami a few decades ago. The same thing that put men down then is the same thing that puts them down today. Besides, bring a rifle.

  9. Glad that’s worked out for you. Duke Venturino (AH)m has written about this.
    Being held by the extractor and not on the case mouth has created its own share of problems.
    I would have expected reliability issues feeding shorter cartridges from a lengthier magazine, in the same way (with a .357 conversion barrel) the shorter .357 Sig can have issues in a 10mm magazine.

    • It just doesn’t happen. The stress put on the extractor by holding the round from plinking down into the chamber is nothing compared to what it deals with every time you fire the gun and it has to rip that case out of the chamber. There’s no more wear on it. It will last just as long as it would have otherwise.

      • Sorry Jeremey but your 100 per cent in error

        “”””””””””””””””””””””””””””””””””””””””The stress put on the extractor by holding the round from plinking down into the chamber is nothing compared to what it deals with every time you fire the gun and it has to rip that case out of the chamber””””””””””””””””””””””””

        Extractors were put on weapons to remove loaded rounds not pull fired cases out of the chamber during the cycling of the action. Yes I agree sometimes (but not usually) they can extract a stuck case or stuck live round but most of the time they fail miserably.

        If you think extractors are necessary to pull out a fired case on the cycling of the action I suggest you remove the extractor on a P38 pistol and then fire it off. You can fire off the entire magazine and the gun will eject every spent case with no extractor in the gun.

        If you still think extractors are necessary take a look at some of the Beretta pocket pistols with their tip up barrels and no extractor. They work just fine without an extractor.

        • Weird.
          None of my bolt guns will cycle properly without an extractor. Neither will my lever gun. I know, it broke once.

        • Yeah that’s super special. Straight blowback guns will work without an extractor and my HK P7 will as well, but a Glock won’t (and the vast majority of pistols with a Browning style locked breech system). The extractor is 100% necessary to pull the case from the chamber, and often it’s stuck in there fairly hard. The force it experiences pulling that case out far exceeds — not even freaking close — the force it experiences holding a round against the breech face so it doesn’t fall deeper into the chamber upon chambering. It’s just a complete and total not-issue. And you can argue theory and assumptions and invented physics equations all day, but in the real world we know you’re wrong because a zillion people shoot a zillion rounds of .40 through their 10mm Glock every year and see precisely zero increase in extractor issues. It’s just not a thing that happens, even if your gut feeling is that it should. Your instinct is simply wrong here.

        • Vlad, your ignorance is exceeded only by your stupidity. Yeah, some pistols will eject without extractors. But that doesn’t make them a good idea. Those little Berettas are direct blow back mouse guns. You carry one. Probably fits your limp wrist a little better anyway. Leave the real calibers to men.

      • Sorry, have to agree with Vlad (Jesus, did I say that?). Tom, that is a BOLT gun! A semi ejects due to the recoil of the fired case pushing the bolt back, not the bolt magically retracting and pulling the case with it. A bolt delivers all that energy to your shoulder, requiring you to then use the extractor to pull the case out. In something like an AR, using gas to push the bolt back, it could be that it would not cycle without an extractor, I couldn’t guess. But any recoil operated handgun does not need an extractor except to unload live rounds.

        And Jeremy, let’s reason together. What is it that you believe causes the slide on a 1911 (or whatever) to move when the gun is fired? There is no gas system, the only energy available is recoil pushing the case back, which pushes the slide back.

        • Insulting Vlad *is* fun, I enjoy it myself, but even a blind squirrel will find a nut now and then. He didn’t say it would damage the extractor, he said the extractor pulling the fired case out was not a player at all, because it doesn’t happen.

        • @Larry that’s simply not true. Pistols with a Browning style locked breech system are supposed to keep the barrel and slide locked together for long enough that the bullet exits the muzzle and pressure drops before the slide begins to separate from the barrel. The result is most of the way toward behaving exactly like your bolt action example, as much/most of the force from the bullet and the gas pushing the case rearwards has dissipated while the barrel is still locked in battery. At this point the slide becomes the equivalent of your manual bolt and it must pull the empty case from the chamber with no help from any gas pressure. And that case was just expanded against the chamber walls with thousands of PSI of pressure and will stick to varying degrees depending on how clean the chamber is and a few other factors. I guarantee you if you remove the extractor from your Glock it will not extract, let alone eject, when you fire it. And Glocks unlock really quickly. Do it on a gun like a 1911 or a CZ 75 or something else with a longer lockup and it won’t even be close. Often with a Glock the case will move like 1/3 of the way out of the chamber, but that’s it. And that’s if it’s clean.

          You guys are spouting off based on your gut feeling whereas I’ve actually done this experiment. You can too. It takes 3 minutes to remove the extractor from a Glock then reassemble the slide without it. Do it. Shoot it. Report back. You’ll see that your wild ass guess as to how pistols like this behave does not match up with how pistols like this behave.

        • So, you failed to mention where the *energy* to pull the case from the chamber comes from, given a firearm which is not gas operated? And how does a fixed barrel .380 pull the case from the chamber? I don’t shoot Glocks, and they are not the only handguns on the planet.

  10. I have read a number of posts about running 40sw in a 10mm Glock and they are all the same. People tell you it is unsafe or wont work yada yada and other people who have run thousands of 40sw through their 10mm Glock with zero problems just keep on doing it with zero problems. The potential problems are theoretical and just don’t happen in practice. I have a G29 and G20 that work fine with 40sw and a G40 that is not reliable with 40sw, probably because of a little more mass of the longslide.

  11. Fascinating article with lots to think about Jeremy. Thank you. Also makes me regret that I didn’t buy a pawn shop G20 for $325 back in November.

  12. The carbon fouling issue is legit but… damned if I can’t be made to worry about it that much.

    Years back I bought a ton of UltraMax .40 because it was on some stupidly awesome sale and I didn’t realize it was garbage ammo. I’ve seen black powder firearms put out smaller puffs of smoke (OK, that’s an exaggeration but it’s a mild one, this stuff was awful).

    That never caused a problem even with 1000 rounds down the pipe creating at least, and now I’m not exaggerating, 10x the normal amount of fouling. This stuff was disgusting yet it caused no such problems that would be a safety issue. In practice it fouled the extractor to the point that it failed before it fouled the barrel and chamber badly enough to be an issue.

    I’d hazard the guess that the excess fouling from running .40 through a 10mm Glock would essentially require an intentional lack of basic maintenance on the gun. I’m sure there are people out there who are this lackadaisical but for me I wouldn’t really consider it an issue.

    Excellent write-up btw.

  13. I’ve been shooting .40 in my model 40 since I got it a few years back. Before that, I shot my model 20 the same way.

    Never a hickup.

    • 5.7? It’s an ice pick. Carry it you want to. Seen one homicide with one. It was a head shot. Execution style. Rather have a .22 LR.

      • Bit late on the comment but Ft. Hood was majority 5.7 for those killed. Not sure on the ammo selection off hand but unfortunately it is plenty deadly and able to stop charging male opponents. Not as useful with capacity limits for NY but anywhere with standard mags it is a consideration.

  14. The only problem I’ve had shooting .40 in a 10mm G20 is plated bullets will keyhole. Even at close range, reloads using Berry’s bullets hit the target sideways. Using a true FMJ causes no problems.

    I’m guessing the more substantial jacket on a FMJ takes the jump to the chamber mouth better. Most plated bullets are very soft pure lead with a very thin ‘jacket’ and will actually make a nice ‘splat’ when shot against a hard target surface like cement.

    I haven’t shot my G20 very much overall, but it has seen more .40 than it has 10mm. Since I don’t have much 10mm brass to reload it will probably stay that way. It’s very pleasant to shoot 180 grain FMJ at 1200 fps and I much prefer to shoot .40 out of a G20 than a G23. The heavier slide makes it much less snappy.

    • Biff, that’s fascinating. But, have you tried those same bullets in 10mm cases, because it did not sound like it. Might keyhole exactly the same.

  15. I have more fun with 44 special then the mag varieties in the same revolver. I’ve often wondered why reduce the loading on the 10mm instead of just getting a .45 ACP? .

    • Don’t own a .40 or even a 10mm but have a few .45 Colts and even a .357 magnum. Why exactly, again did I need a .40?? My SIG P320 is easily convertible. Next time I have a spare $400 I’ll try the conversion and see for myself if it was worth all of the hoopla.

  16. you do this because you are an idiot
    it’s nice you produced a little ‘article’ just to make sure everyone knows
    before you wrote it everyone just suspected

    • How precious – he, who can’t capitalize or use punctuation calls someone an idiot, based on an article describing long term personal experience.
      You are not Nick (Foghorn) Leghorn. That guy’s got class.

  17. I’ve done the same thing as an experiment shooting .380 out of a Glock 9mm.

    It works and is perfectly safe for all the same reasons. The .380 is nominally smaller but it works fine with the sole exception that with a factory RSA the gun won’t cycle far enough back to chamber another round.

  18. Spend half the year in NW MT with the bears and huckleberries, the rest of the time in urban AZ. I carry 10 mm solid cast for bears in MT, but the rest of the time I shoot .40 in my G20. I find I shoot either caliber better out of the G20 than I do 9 mm with my lighter G17. Completely happy with my experiences shooting .40 in the G20. No problems whatsoever.

    One reason that being able to shoot .40 out of a G20 is that the range of ammunition available is substantially greater. Not solid core bear ammo, but the most modern self defense ammunition. And, the .40 is a lot cheaper, though around Missoula, 10 mm FMJ target ammo has substantially come down in price, with several local manufacturers producing it (actually, all the way down US 93 to Salmon, ID).

  19. I believe it was the .38 Super that originally had accuracy issues way back because the extractor held the cartridge and there was not being a correct seating of the case mouth.
    And it was Taffin who discussed it.

  20. Can’t argue with success. If it is mechanically sound and no “kaboom”, screw your detractors and arm chair generals. I once shot a 9mm in a Beretta Brigadier 40SW. No Kaboom but it made different sound but the case ejected and expanded beyond repair but the bullet went down the barrel and hit the target. Not much in the accuracy department but no damage to gun which was a robustly built Beretta with a very thick chamber. It was my service weapon in USCBP. The lesson to me was simple: be ware of what magazine goes into the weapon, the Beretta mags for the 92 and Brigadier are interchangeable.

  21. BTW there was a .40 cartridge in development before the 10mm, it was in the late 70’s and it was called the .40 B&S and it’s dimensions were almost exactly what the .40 is today. Yes the .40 came from shortening the 10mm and using a small pistol primer instead, but the first semi auto .40 concept was more akin to what we have today with the .40 S&W, not the 10mm.

    As for .40 in a 10mm, I won’t say it’s a terrible idea BUT relying on the extractor to hold the .40 in place isn’t really what it was designed for, so yes it’ll work until it doesn’t. Plus there’s pretty cheap 10mm nowadays, you can get S&B for $14-15 a box of 50, which isn’t as cheap as most .40 but it’s probably a better for your gun. A .40 S&W conversion barrel can be had for not that much money, depending on brand of course, and would make it a more legitimate option.

    Personally I think the .40 is better than the 10mm is, because both loaded hot there’s not a ton of difference in power (G20 180gr @ 1350 vs G35 180gr @ 1300) and if I want more power, I’ll grab the .44 Mag. I guess my point is that rather than shoot .40 from a 10mm, just handload the .40 warm and not worry about 10mm.

  22. I understand you have said this applies to Glocks. What are the chances this would also apply to a PCC? I guess each gun would need to be inspected to insure it would work fine. Some would some wouldn’t?

    Since there is tolerance build in to SAMI spec chambers and bullets, wouldn’t most 40mm not actually bottom out in the chamber anyway? If the extractor can handle .1mm of space, shouldn’t it be able to handle 3.6mm

  23. A .38 Special in a .357 magnum or a .44 Special in a .44 Magnum are the true exception to this article. The case diameter of the .38 Special and the .357 Magnum are identical the same as the .44 Special and the .44 Magnum. The case lengths of the Magnums and the Specials are different which prohibits putting a Magnum in a Special cylinder or in a single shot chamber. Now the problems with semi-automatics that must retain the gas pressures to operate the slide to eject the cartridge with enough inertia to permit time for the new cartridge to load and with enough spring pressure to seat the new cartridge. Now before firing; your magazines must be kept clean because dirt will slow down the loading speed and inertia that any loss will cause loading jams. Also your magazines springs need to be maintained. Again before firing; the type of bullet could cause a problem. Most semi-automatics, from ages ago, were designed for “full metal jacket” or “round nose” bullets that slid smoothly through the magazine. But the non-standard designs of “semi-wadcutter” and “jacked hollow point” bullets can cause resistance to the smooth magazine feed and the loss of speed of the bullet rise can cause loading jams. If the case diameter is only a few thousands smaller the gas pressure will be lost decreasing the inertial force to overcome the slide spring and you could end up with “stove-pipe” cases instead of ejected cases. If the case diameter is only two thousands of an inch larger the interference resistance will cause loading and ejecting problems. These issues aside from the barrel chamber pressure means do not attempt even loading .223 Rem. into a chamber designed for 5.56mm X 45mm. There is too much invalid ammunition information on the internet that is not from reputable manufactures of ammunition and firearms chambered for non-commonly known calibers.

  24. I have a 1911 Springfield with the Clark 460 Rowland barrel it took a little effort. Had to ditch the titanium firing pin so it is no longer drop safe and change put the recoil spring don’t remember what pound it has been a while. But I shoot 45acp or 460 rowland with no issues whatsoever. Of course I probably have only shot around 200 rounds of 460 and all underwood Hardcastle or Buffalo bore Hardcast as this is my bear gun here in alaska.. 45 acp shoots like a 38 with the huge muzzle break lol


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