Ask Foghorn: What Parts Should I Use when Building an AR-15?

Many, many many readers have written in over the last couple weeks asking roughly the same thing:

I was reading your article on Best Budget AR 15 and I tried to click on the build recommended links but most don’t seem to work now. Do you have an updates? or suggestions? I am very interested in learning more and trying to build my own.

So you want to know what my build list would look like these days? Let me knock you up a list . . .

First things first, my normal recommendation for people building an AR-15 is to build the lower yourself and buy the upper receiver complete and already assembled. And I’ll be following that recommendation with my parts list.

The reason I suggest buying the upper receiver as one complete pre-assembled part is that when you start mucking with headspace and gas tubes and trying to get the proper torque with barrel nuts, there is a whole lot more that can go wrong if you don’t get it close to spec. Not even the professionals always get the proper torque on the barrel nut (which leads to decreased accuracy and in some rare cases the barrel flying apart), so expecting a new AR-15 builder to get it right on the first try might be asking too much. But with the lower receiver, there isn’t anything that will kill you or decrease accuracy if you get it wrong.

There’s also a lot more to upgrade on the lower receiver. With the upper, the only thing that you would really be tweaking are the optics and handguards. But with the lower, you can do anything from getting a new trigger to swapping out the stock. And each change makes a huge difference to how the rifle handles.

Oh, and if you don’t know how to put together an AR-15 lower receiver, I’ve got an article for that. Now for the parts list (skip to the bottom for just the list and no descriptions).

Lower Receiver

The lower receiver is the bit that holds the gun together. And, in the eyes of the ATF, it is the gun. Which means you’ll need to get yours from an FFL if there isn’t a helpful citizen available to sell you one in a “private party” transfer.

Aero Precision is my current favorite manufacturer, they make parts for Boeing aircraft and in their spare time they started precision manufacturing lower receivers. I used one of their lowers in my competition rifle, but their rollmark seems to have changed quite a bit since the early days. Heck, back then they didn’t even have a website. Next on the list is Franklin Armory, whose lower I used in my testing rifle and looks pretty cool.

The good news is that no matter who you pick, as long as they’re not some fly-by-night operation you’re fine. Lower receivers are all the same, built tot he same specs and nearly identical from one to the next in terms of everything from dimensions to metallurgy. The only difference is the rollmark and the safety selector indicators on the lower. Unless you go with a funky polymer lower, that is.

Lower Receiver Parts Kit

If you look at my article on building a lower receiver, you will quickly find that there are a ton of little pins and springs that go into one of these guns. So rather than going out and buying each pin individually, the smart move is buying the parts all in one go. DPMS’ parts kit is the best I’ve used, so long as you immediately throw out the trigger and the grip. Everything else is golden.

Trigger

The trigger should be the main focus of any upgrade to your rifle. Its where you will notice the most increase in accuracy and speed for the least investment, and its one of the easier parts to swap out. I’ve been a huge fan of the ALG Defense QMS trigger, as it provides the best balance of performance and expense to the new shooter. Plus, the thing is tuned by Geissele’s people before it leaves the factory for extra awesomeness.

Grip

The grip on an AR-15 rifle is all about comfort. You need to be able to comfortably grip the gun and have your finger positioned perfectly on the trigger in order to get the most accurate shot. For that reason, I really like Magpul’s MIAD grip kit. It gives the shooter a grippy surface for better holding onto the gun, and allows them to change the shape of the grip to match their own hand. Plus, it just looks awesome.

Buffer Tube / Receiver Extension

The fiddly bit that sticks out the back of the rifle, whatever you call it, needs a little extra attention than most parts. There are two versions, the “mil spec” and the “commercial” version. The only difference is that the commercial version is slightly larger than the mil spec variety, but whichever one you choose you’ll need to make sure your stock matches up. That’s why I default to mil spec, since its less likely to be out of spec. DSA makes a complete kit that has everything you need for this section, including the rear plate, buffer spring and buffer.

Stock

Not to be a Magpul fanboy, but their stuff is the best on the market in terms of comfort and reliability. And for those on a budget, their stocks are actually pretty reasonably priced. My current go-to stock is their MOE Carbine collapsible stock, which might be a little more expensive than the standard looking stocks but makes it up in the cool factor.

Upper Receiver

For the upper receiver on my “screwing around / testing stuff” rifle I’m using a pre-ban DPMS M4-style upper (yay New York). I personally find the fixed front sight post and carbine length gas system fits my needs perfectly, and I get the feeling I’ll love it even more once I chop the barrel down. Unfortunately, those have been out of stock for quite some time. But there are alternatives out there. Like the Del-Ton upper that is nearly identical and costs a lot less (if it ever comes back in stock).

Iron Sights

Since the upper comes with a fixed front sight post, the front sight is unnecessary. However, a rear sight is a good idea if you actually want to hit anything. Magpul makes a back-up iron sight that costs around $60, but its lightweight and gets the job done. I really like it.

The List:

That comes to a total of roughly $792 before taxes and shipping, but its a rifle that has all the bells and whistles of a $1,000+ gun.

Now, keep in mind that just about everything is sold out right now thanks to the rumors of impending doom and gloom. But as soon as this all blows over, expect there to be a rather large surplus of parts. That’s the nice thing about panic buying — it saps the cash out of the suckers and creates a surplus (and therefore discounts) on the other side of the hump.

[Email your firearms-related questions to “Ask Foghorn” via guntruth@me.com. Click here to browse previous posts]

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About Nick Leghorn

Nick Leghorn is a gun nerd living and working in San Antonio, Texas. In his free time, he's a competition shooter (USPSA, 3-gun and NRA High Power), aspiring pilot, and enjoys mixing statistics and science with firearms. Now on sale: Getting Started with Firearms by yours truly!

47 Responses to Ask Foghorn: What Parts Should I Use when Building an AR-15?

  1. avatarLance says:

    Buy all the magpul items you want Nick but leave the milspec one alone want prices to drop so I can buy them LOL!!

  2. avatarjwm says:

    Use all of them. This is not the item you want to wind up with leftover parts when your done. Didn’t work well when my uncle rebuilt the motor on his Studebaker and had parts left over.

    Can’t imagine a finicky beast like an AR would work well with missing parts.

    • avatarAlphaGeek says:

      What if I buy an LPK, and it comes with a shite trigger, but I also buy an upgraded trigger set? Do I have to use them both?

      If I do, will it create one of those “select fire” guns I keep hearing about, like a double-barrelled shotgun with dual triggers?

      • avatarOODAloop says:

        Dude, only one will fit in at a time, dream on…

        • avatarAlphaGeek says:

          Clearly I have been playing too much Borderlands2. Next thing you’ll tell me is that magazine-fed rocket launchers don’t actually exist.

    • avatarWLCE says:

      well no gun works well with missing parts LOL.

      ARs are very simple to build and you will know when youre missing a part. parts diagrams are also very easy to find.

      building a AR is easy. finding different parts that work harmoniously with each other requires a little bit more skill and experience.

  3. avatarAlphaGeek says:

    Nick, did you actually keep a straight face when you typed in the cost of an AR lower as $79.95?

    I thought I was doing well to get two Kaiser Defense lowers at $150 each before the prices REALLY started to go up.

    • avatarDyspeptic Gunsmith says:

      That’s what I gave per receiver when I ordered four of them just before and just after election day.

    • avatarLars says:

      Ya, I’m a known AR and AK parts and accessories seller on armslist and I can’t tell you how many offers I get for AR lowers even when I have no ad up for anything. I have a moderate stock of them but I’m looking all the time to buy them and have not found one in over 2 months in my area or online other then 300-600+ ones on armslist.

      • avatarAlphaGeek says:

        Any suggestions on where to look for a good quality lower parts kit, ie DPMS or equivalent? Even better if I can find a couple of LPKs that come without trigger groups since I’m going to upgrade those anyway.

        • avatarMike in NC says:

          Any suggestions on where to look for a good quality lower parts kit

          Can’t help with “where”, only “when”… in the Future!

          Before all the troubles DPMS and a few other brands were at the bottom of the heap price-wise and you would not save trying to get something sans trigger group. If you plan to upgrade to a two-stage trigger like RRA or CMMG (to name just a few) then just get that as a complete two-stage LPG kit when they become available again.

  4. avatarCasey T says:

    Has anyone else tried the Mako GL Shock stock? I got one and really like it so far, though I’m still building my upper so I can’t shoot with it yet.

  5. avatarTacticalDad says:

    Please post where these parts are in stock. (lol)

  6. avatarHoustorm says:

    I luckily purchased a stripped lower in November for $89.99; that same lower at the same shop now is $289.99. I had originally planned on building my rifle over a decent period of time, but I admit that I pretty much bought everything in the past month through a combination of Midway, Brownells, and my LGS. I built the upper myself, and I think it is a rewarding experience, and much cheaper to do it that way. I am friends with someone that builds their own race guns, and he was able to check my work and make sure I didn’t screw things up. If you are going to build one yourself, ITS Tactical has a very easy to follow set of videos to aid in your build. Good Luck and Have Fun.

  7. avatarWLCE says:

    before the gun doomsday, you could find a LMT upper for 400-450 bucks, which are miles better than Deltons. I purchased one LMT 14.5″ for 400 bucks and a 16″ for 425 last summer.

    now youll be lucky to find any of those individual parts in stock…

  8. avatarPeter says:

    I would suggest going with a Vltor A5 buffer/stock , it just works with pretty much everything,, no juggling different buffer weights to get the gun to cycle reliably.
    It is a bit pricey but worth it.

  9. avatarJavier says:

    Great list Nick. Too bad it’s all out of stock.

  10. avatarThpbltblt says:

    I don’t see a forum anywhere… When I remember what my question was, how do I go about “Asking Foghorn”?

  11. avatarGeoff says:

    I miss the days of $49 PSA lowers

    • avatarOODAloop says:

      Don’t we all. Remember when you could get a complete 16″ middy upper for ~$379? I built a complete polymer AR for under $500 this summer. Ahhh, these are the sorts of things that turn into the fairy tales that your grand-dad would go on about…

  12. avatarDaniel Silverman says:

    Nice list Nick.
    On. Side not have you thought of consolidating your videos down to one single post. There is great stuff on the AR build plus reloading etc.
    It would be great to make it easier to find.

  13. avatarIn Memphis says:

    Any opinions on Wilson Combats drop in trigger, the TTU? Is it worth the $200+

  14. avatarG2 says:

    Thanks for producing the video! I couldn’t help but smile and laugh each time you pronounce detent “day taunt” instead of “dee tent.” Keep up the great work for TTAG.

  15. avatartcp1 says:

    Any reason you didn’t put any focus on the BCG and charging handle?

    Items like the BCM Gunfighter handle make a great upgrade for just usability, and I personally am confused at the usefulness of all the various BCGs out there (i.e. the FailZero stuff)

    • avatarAPBTFan says:

      Personally I think the “difference” between BCG’s boils down to marketing. LuckyGunner just did a torture test with four bone stock Bushmasters where they put 10,000 rounds through each one in a matter of days and there were zero problems with any of the four BCG’s.

      There is a precise science and formula in marketing that works very well for getting someone to pay more money based on perceived value. I know because I’ve been suckered into replacing plenty of perfectly good parts that otherwise would have served me just fine. The AR platform, with the hundreds and hundreds of possible upgrades, is disgustingly easy to waste money on.

      If you’re thinking of a new BCG I advise you to go ahead and do everything you can to wear out the one you have. If and when you manage to wear it out then THAT is the time to ask if you got your money’s worth out of the stock BCG and whether a more expensive one will be worth the money compared to the life you got out of the stock BCG.

      Some upgrades make an immediate difference. Like you, I bought the BCM charging handle and love it because it made an immediate, fundamental difference than the stock part. To me when it comes down to wear parts that offer no immediate or fundamental difference in operation, unlike a charging handle, I want to get my money’s worth out of the stock part I already paid for before considering the value of a well marketed fancy part.

  16. avatarDyspeptic Gunsmith says:

    Most of the problems in torque specifications on the barrel extension and the castellated nut holding the barrel into the upper come about because people refuse to use a torque wrench. The torque specs are really quite clear in the Armalite or USMC/USA/DOD/Colt specifications. But for some reason, there are too many people who refuse to obtain the required tools to do the job correctly.

    The first thing a guy must have to torque to spec is a torque wrench. 1/2″ drive, one required, I like the analog or “micrometer” type. Without a real torque wrench, you’re simply guessing as to how much muscle you’ve used to screw something on. If a guy wants one, go get a Sears Craftsman wrench if you want to go economical but reliable. Look in Grainger’s if you want to spend more. If you want to spend more, get one with a calibration cert.

    Do not buy a Horror Freight torque wrench. You’ll be no better off than using a breaker bar and guessing.

    Second thing is the correct tool to torque the extension or nut on. All of these are available through Brownells.

    Third thing required is a fixture on which the upper sits – the fixture goes into a vise (for torquing the castellated nut) or a barrel vise (for the extension) and the upper goes on the fixture and gets pinned in place. Now you can apply torque to the barrel nut. A common shop vise with lead soft jaws could suffice to hold the barrel while the extension is torqued on.

    This is pretty easy stuff – I hardly even rate it as being worthy of a gunsmith’s attention. Someone who can change a tire on a car should be able to do this stuff. But, seeing how many people in today’s society seem to possess a level of mechanical talent that allows them to screw up an anvil with a feather, perhaps the admonishment to buy a completed upper/barrel setup is best.

    It tends to limit your choice of barrels, tho.

    A couple other points for AR noobs:

    Get real roll pin punches. If you use pin punches to punch in the roll pins that are all over AR’s, you typically will slip a punch off the pin and muck up the aluminum around the pin hole. Again, you can look in Brownells or MidwayUSA to find these.

    LPK’s: I’ve used Colt (with Gen-Ewe-Whine Colt prices), DPMS and cobbled together my own parts from generic sources for roll pins, spring, etc. They’ll all work.

    Triggers: The GI-spec triggers are horrible. Uniform crap. The case on them is so thin, if you try to stone the hammer and sear as you would in classic guns, you’ll blow through the case and end up with a trigger pull that feels like you’re pulling a spoon through cold peanut butter.

    I now just order the non-adjustable Geissle 4.5 pound trigger group (SSA) for non-match guns and call it good. I like two-stage triggers – other people might not. For those who like single stage triggers, look at the Timney products.

    Your gas key should be staked. I recommend that most people who are noobs buy their bolt carrier group already assembled. If you’ve had some training, you could buy a naked bolt, naked carrier and piece them together. If you’re good with a punch, you could stake your own gas key. If you’re not, you’ll need to buy/rent/borrow a fixture that allows you to stake your gas key.

  17. avatarLars says:

    All stripped lowers are the same. No one brand is better then the other. Out of all the ARs I’ve built the brand of lower has been meaningless other then if someone has a preference to a certain logo.

    • avatarAlphaGeek says:

      Especially since these days most of them are made by Aero Precision (vast majority), Kaiser Defense and a very few others.

      From everything I have learned, the only ones to avoid are from small operations which claim to have come up with some sort of proprietary improvement and make them in-house.

    • avatarHuman Being says:

      Unless you need an ambidextrous/sinister lower. Just sayin’.

  18. avatarC says:

    he might want to invest in a wood mallet.

  19. avatarensitu says:

    I was a 45B3H Instructor at APG. I trained 1000′s of “Trainees” Domestic and Forgine. I was also a 45K3H.
    On a lazy sunday morning I could slap together 3 ARs from parts, it aint rocket science. Using a Complete Upper it is a 20 minute build. Remember the AR was designed for US Soldiers so if you can assemble a stereo system you can build an AR, just READO the EFFING directionos!

  20. avatarEric says:

    what’s an AR part?

    • It’s a mysterious creature that once freely roamed the earth. Sadly, it is now extinct. Although there are still examples of these creatures available for viewing, it seems there are no examples available for holding. These creatures are so rare, some claim they are more like the Unicorn, just a myth hyped up by true believers. There is a rumor going around that a documentary is being made. The working title is The day the AR Parts were hunted to extinction

  21. avatarNathan says:

    Nick, was it that optic that you have on the rifle in that picture?

  22. Heya i’m for the primary time here. I came across this board and I find It truly useful & it helped me out a lot. I hope to offer one thing back and help others like you aided me.

  23. avatarDV says:

    I just got a build last week, similar to your template (complete upper, stripper lower, LPK). Spikes ST-15 mid-upper, PSA stripped lower and LPK. Total ~ $750

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