CapArms Question of the Day: Which Rail System for Your Rifle: M-LOK, Keymod or Picatinny?

“M lok has addressed some of the problems that key mod had initially and also looks cleaner on the rifle while seeming to have a more aftermarket availability for the time being,” button_up_chuck writes on Daniel Defense’s Instagram page . . .

I also see more rigidity issues due to the mounting attachment of key mod. Some aftermarket manufacturers do not use the correct tolerances and attachments fall off. It leaves more room for things to be out of spec. While M lok is more simple and seems to be easier to manufacture within specification.

Hey! What about poor old Picatinny? Anyway, which rifle rail system do you own, which would you buy now, and why?


  1. avatar Gov. William J. Le Petomane says:

    Quad rails suck.

    1. avatar Charlie Mike Mike says:

      What is this “key mod” they speak of?

      1. avatar Gov. William J Le Petomane says:

        I’ve been to Key West, Key Largo and even Key Biscayne, but I have no idea where KeyMod is.

        1. Key Mod is in the North East.

        2. avatar Gov. William J Le Petomane says:

          I see. How do you get there? On the Picatinny Rail?

        3. Unless you run into an m lock. In that case, you want to take the off set around the red dot mount.

        4. avatar Gov. William J Le Petomane says:

          I’ve heard that’s the scenic route, what with all the holographic sights.

        5. Depends on the MOA. 2 to 4 MOA leaves a a good field of view. Anything above that and you can’t sight anything past 100 yards.

        6. avatar Gov. William J Le Petomane says:

          Either way, just make sure you bring fresh batteries or you might be SOL.

        7. Not necessarily. Once you get over the mount, through the buffer tube, and beyond the forend, you’ll be barreling right on target.
          Coast on in on your back up irons, and recharge at the 5.56 lower. The 223 is a little more laid back but either way, make sure to spend the night and take in the 300 blackout.

        8. avatar matty 9 says:

          you guys are killing me

    2. avatar McBell says:

      Picatinny Quad has the fewest issues with accuracy of the 3 when it comes to mounting laser sights and other aiming devices or range finders like the one from SilencerCo.

  2. avatar BC says:

    I like picatinny quad rails myself. I don’t hang a bunch of crap off my rifle; most of the rails are covered with, well…covers. But I have big hands and most forends seem to be really thin these days. So the quad rails give me something I can really grab a hold of.

    1. avatar BM says:

      You should check out the Aero Precision Rails. They have a fairly large diameter.

  3. avatar James Earl Hoffa says:

    I’ve use the key mod handguard from SLR for over 3 years now and have had no problems even in 3-gun competitors using my rifle built with keymod handguard. Those three gun guys and girls bang the heck out of their rifles not as much as military use or SWAT team law enforcement use however I have failed to see anything come off keymod handguard. So if you’re using the rifle for home defense and target shooting you will have no problems with keymod. I feel comfortable using a keymod handguard in battle as well. I was in the 82nd Airborne for five-and-a-half years in Iraq and Afghanistan so I know what a combat weapon system goes through. Now obviously after the tests were completed on keymod vs mlok the M lock system is definitely more rigid. But in all honesty who in the civilian populace is going to beat a rifle the way an Army Ranger is going to beat up a rifle or even a rifle in basic training not many. I like the look of the keymod and the handguards seem to be lighter because there’s more material cut out which seems to be what everybody’s going for now a super lightweight AR-15.

    1. avatar Hoosier says:

      Good post.

  4. avatar Ralph says:

    I only have one AR and it has a Pic rail. It’s meh.

    What I would prefer is a full retro civilian M16A1 with no rails, triangular handguards and the so-called “carry handle.”

    1. avatar Anner says:

      I’ve seen a couple Colt SP-1s for sale here and there. 1 was for trade online as a private sale, the other at an LGS in west Texas. There are gems out there.

    2. avatar Norincojay says:

      Brownells has retro 1-12 AR barrels for sale with FSB, barrel nut, weld spring and end cap all ready to go! They even have stripped carry handle uppers.

      1. avatar anonymoose says:

        Brownells had a lot of issues with their retro barrels over the past year. There was a recall not too long ago. I’d look elsewhere. Green Mountain has true M16A1 barrels (you have to drill the pinholes for the gas block though) and there are still a few places offering A2 barrels without M4 feedramps (but not too many).

    3. avatar anonymoose says:

      It’s a carry handle. Anyone who insists it isn’t a carry handle is a moron. It was intended as a carry handle, as a lot of guns of the 1950s had carry handles. US doctrine is not to carry guns ever by the carry handle, even heavy guns like the M240. It is not a “sight bridge” or whatever other crap they try to teach you. They are handy if you are moving things around an armory or unloading multiple guns off a truck. Carrying it by the carry handle does make you unready for engagement, which is why they don’t allow it.

      1. “Carrying it by the carry handle does make you unready for engagement”

        About as unready as having it slung. And I’m pretty quick with it slung.
        I’d toss the M4 up by the carry handle and catch it in fire position. But I’m a bad as mofo so…

  5. avatar rc says:

    I’ve got one of each (keymod and mlok)…I guess mlok is the new VHS.

    Oh, I’ve got a Ruger SR556 with picatinny rails, but that one doesn’t count, since I hope to sell it.

  6. Picatinny Rail – I can mount what I want, where I want, without any adapters.

    And most people have too much junk on their ARs anyway. My main AR has a Magpul drop-in on it, and just has a light and vertical foregrip on it. Keeps it light. Don’t need much else.

    1. avatar Anner says:

      Same on the Magpul foreend. I hang a VFG and tiny streamlight TLR-3. It keeps it slick and lightweight.

    2. avatar Ardent says:

      Sounds like mine Locke: white light, vertical foregrip, red dot and fold down iron backups. It’s picatinny, and not too much junk.

  7. avatar Shire-man says:

    I have each. No real preference functionally.
    Aesthetically I’d rank: Keymod, picatinny, M-LOK.
    Love that industrial shelving look. Since I don’t mount jack shit to my rifles appearance is all it’s worth.

  8. Picatinny on a monolithic. No complaints as it’s a carbine length so the weight doesn’t stack on me much.

    I’m going to wait out the whole keymod vs mlok until I must buy a new upper or BCM starts making mlok handguards.

  9. avatar gargoil says:

    we need something sleek, slim, and EASILY field removable. until that happens i’ll keep picatinny. ive seen some QD stuff but its so damn bulky. im not really a “looks” kinda guy when it comes to rifles, pistols is a different story. you’d think it would be the other way around but no.

    1. avatar pieslapper says:

      Hmmmmm. Duct tape. It’s sleek and slim, and fulfills your “looks” requirement. Whip out your blade of choice and it’s easily removable in the field.

  10. avatar Joe R. says:

    Picatinny. You have to fiddle with the other stuff. If you want to sling an M203 (instead sling a Spike’s Tactical Flare Launcher) you slide it on a rail, you don’t, first, mount your rail on your rail, then slide it on your rail, double check the fit/finish/placement and then move all of the pieces around.

    “Too much mounted on your AR” can happen. What usually happens first is that you ‘don’t have enough ass for that”. Here’s your straw, suck it up. I mounted a Spike’s launcher on my AR (lost in a fiery boat wreck at sea) just because after carrying an M203, a slicked-down AR feels like it’s missing something. I was shooting high all the time. ; )

  11. avatar Binder says:

    Just a 1-4 scope, usually set at 1.5, so no rails.

  12. avatar Joe R. says:

    G R E A T pic btw.

    Thanks DD, and TTAG.

    Makes me want to go to the range. Who’s with me. Everybody get in the truck.

    1. avatar Rincoln says:


  13. Got a full length key mod handguard.
    Don’t have any adapters
    If it’s not important enough to make a direct mount, then it isn’t important that I mount it.
    I have a BCM Gunfighter short vertical grip, a BCM QD sling mount, and plans for a future light mount, all direct Key Mod.
    I could get a picatinny off-set light mount to come off the top rail, but no adapters for me.

  14. avatar Mark in NM says:

    What’s a rail? “In Russia, rail rifles YOU!”

    Yeah, AK guy, but it’s all good. Real men hold flashlights and lasers in their teeth.

    1. Real men fight in the dark.

    2. avatar Gov. William J Le Petomane says:

      Real men hold the reins in their teeth, know how to work a lever and say cool shit like, ‘Fill your hands you son of a bitch!’

      1. …riding bareback with the reins clinched in your teeth!

  15. avatar Somebody says:

    Well, the Picatinny rail on the upper receiver meets all my mounting needs. The hand guard only exists to protect my hands from the gas block and gas tube.

    Do remember that Picatinny doesn’t always mean quad rail.

  16. avatar Hooahberry says:

    Have 1 AR15, it’s an SR556 from 2014, so Troy Picatinny quad rail is what it’s got.

    Have on it: vertical foregrip, Larue/Harris bipod, Streamlight weapons light, and a bunch of Magpul rail covers.

    I had hoped to get an SR556E because I liked the slimmer forend, but the SR556 at the on-base exchange was too good to pass up (cheaper & no sales tax!) The quad rail’s kinda heavy, but it does reduce the low recoil of 5.56 even lower.

  17. avatar justin says:

    Mainly Picatinny rails.
    I have a Sig516 Gen 1 with a very heavy Quad Rail. Proprietary Sig forearm with 1 aftermarket option IIRC,
    A PSA M16A4gery with a KAC Full Length Rail, but I wanted this for my A4gery and it is still lighter than the sig,
    And a PSA Carbine length with the Magpul M-Lok MOE Forearm with some rail segments on it.

    I think if I bought another upper, (still have a Clinton might be President Lower hanging around) that I would go with longer M-LOK forearm with a 12 o’clock picatinny rail for weight reduction.

  18. avatar Pwinky says:

    Only have 1 AR and it’s got a 1/2 length pic rail on the top. Don’t plan to mount a bunch of gew gaws up front so perfectly fine with just a regular magpul hand-guard.

    I don’t enjoy gripping a quad pic rail (tried it on a friend’s rifle, hated it) so if I buy another one I’d want it to be M Lock. I like Magpul and rectangles look better than phalluses (key-mod).

  19. avatar Heartbreaker says:

    I have exclusively M-Lok. Lightweight, thin and looks good. My ar15 has only a small piece of rail for when a bipod is needed, so I don’t have any need whatsoever for a bulky, heavy cheesegrater, and I don’t like the look or function of Keymod.

  20. avatar strych9 says:

    I use pic rail. Only mounts some covers and a foregrip/bipod but it was on sale and gets the job done.

  21. avatar Parnell says:

    Picatinny and I’m perfectly satisfied with it. Only mount my iron sights, a light and a vertical grip.

  22. Just thought of something for anyone concerned with the strength of the key mod. If you are going to use a rail section anyway, get the longer section that has an extra fastener point.
    The 3″ attaches at two ends. The 4″ has a third point in the middle.

  23. avatar M1Lou says:

    I prefer mlok. The problem is there seems to be a lot of keymod deals after that report came out that mlok was substantially better than keymod for durability.

  24. avatar Aaron says:

    I’ve got some Picatinny and quite a few Keymod equipped guards. On two of my Keymod rigs, I’ve actually gone to the trouble of a Keymod attach picatinny rail section to mount an accessory. I understand the logic of M-LOK being an enhancement but will reserve that for future builds. Not worth the cost to convert my gear.

  25. avatar Darkman says:

    Have all three. Like them equally. Haven’t any issues with any of them

  26. avatar Blake says:

    Small hands so the cheese-grater pic rail is out. One keymod and four MLOK guns.Keymod mounts with less pre-fit but MLOK is more available and seems to be winning.

  27. avatar Norincojay says:

    I like both Keymod and Mlok. I have several of each. I’ve never once had an issue with an accessory fall off either. I dislike picatinny except on top to attach sights. Even then I like the SLR rails were they only have the pic in front and back with Mlok in between. That’s my fav. The only reason I like Mlok over Keymod is Magpul AFG and their type 2 Mlok covers. I like Bcm short vert grips, but not as much. Seekins and Odin have nice AFG but they are $40 though aluminum. So I literally pick my front rail on which style forward grip I want on a particular build.

    I remember reading stuff a few years ago predicting the demise of Keymod. I guess people still are.

  28. avatar Eric Lawrence says:

    The AR’s I have are built like the M4A1 and SOPMOD Block 1 I was issued. One has the M4 plastic handguards and the other has picatinny rails with Knights rail panels. How we stacked bodies without Keymod or M-Lok I’ll never know. If I was to build a new rifle I’d choose M-Lok. I trust the analysis Crame NSW did and their choice was M-Lok.

  29. avatar GapharmD says:

    Picatinny is too bulky and heavy. I have a few of each. Never had s problem with key lock or accessories. I like mlok better for looks.

  30. avatar None says:

    Just pulled my DDM4 rail off for a BCM KMR in Keymod. I’d prefer M-Lok, but since I don’t attach anything on my forend (no back up irons, zip ties for the light) the KMR was light and cheap.

  31. avatar Kaban says:

    Real men use WP side mounts, hehe.

    (seriously, nothing but cheesegrater for upper portion, because scopes. Anything else is almost irrelevant, but you simply can’t mount your optic solid enough).

    1. Top rail is for stuff. The rest is for your hand. Don’t forget the BUIS that you will never use.

      1. avatar Kaban says:

        >>The rest is for your hand

        That’s why I don’t care for quad rails. Occasionally, even Tier 0 chairforce operator has to fire the gun ungloved!

  32. avatar RetroG says:

    I prefer the KeyMod, but probably because it came out first and that’s what I already have. After that, M Lock, then no rails then the cheese graters.

  33. avatar Cuteandfuzzybunnies says:

    My latest build Mlock. One before keymod and first at picatiny

    I doubt im the only guy with all three.

  34. avatar Herp says:

    Rail systems are for suckers.
    Irons on the receiver are best.
    Hand guards are for grabbing.

    1. I have my irons, front and rear, mounted on the hand guard. That gives me a longer radius than having them both on the upper.
      I have seen no AR build that can guarantee the free float hand guard and the receiver are perfectly in line. So having the front sight on the forend and the rear sight on the upper will not have perfect windage.
      Also, with my rear sight on the hand guard, it clears the scope since my eye relief is all the way back.

      1. You wrote, “I have my irons, front and rear, mounted on the hand guard. That gives me a longer radius than having them both on the upper.”

        I’m trying to figure out what you mean. I think you meant SHORTER sight radius, not longer sight radius. If you have a 12-inch handguard, putting both iron sights on the handguard only gives you only a 12″ sight radius, which is much SHORTER (and thus less accurate) than if you’d put one on the handguard and one at the rear of the upper receiver, which would give you an 18″ sight radius.

        You also wrote, “I have seen no AR build that can guarantee the free float hand guard and the receiver are perfectly in line. So having the front sight on the forend and the rear sight on the upper will not have perfect windage.”

        Not true. Iron sights are adjustable for windage, so as soon as you sight them in once to adjust them, you’ll always* have the correct windage (*yeah, I know, until the wind starts blowing differently, but that’s when “Kentucky windage” enters the picture). Even if you put both your iron sights on the handguard, you’ll still need to sight them in to adjust the windage, so you’re not even saving any time. You’re giving up accuracy or precision by using a much shorter sight radius (12 inches instead of 18 inches), and I don’t see any advantage — unless you’re eyes are so farsighted that you need to put the rear sight farther away from you, but peep sights don’t work well when you place them so far forward. There are better solutions for people who are farsighted (red dot sights).

        1. You misunderstood.
          When I said upper, I referred to the receiver, which is only about 5″. My buis are 10″ apart on the contiguous handguard.
          I know you can adjust windage, but the handguard rotates around the barrel nut. You can eyeball the top rail before loctiting it down but that is just eyeballing.
          I want a free float forend that is proven in line with the upper before I put my rear sight behind my scope.

  35. avatar Gruney says:

    Looks like Key Mod and M-lok are going to end up in a Betamax vs VHS scenario. KM got there first, but ML seems to be gaining in popularity. Now that test came out that ML is stronger so all the operators operating operationally are going to crush and melt their KM and get ML.

    I have a Seekins forend with pic rail on top and KM elsewhere. I have a front sight mounted to the pic rail, so haven’t tried the KM. I think it will be good enough to git ‘er done.

  36. avatar Evan says:

    MLOK. Picatinny quad rails were great, when that was than only option besides classic handguards. Now, with what is available, they are just cumbersome and sharp edged. Placing covers for grip just add to bulk and is counter-productive. KeyMod was a great solution, except mounts aren’t quite as secure in more active environment (not referring to range). Besides that, they are hideous. Look like my shelving unit in the garage. Might be a good place to mount a garage ready rifle…
    M-LoK, fixes those issue. Sleeker, more comfortable, more secure, sexier. My opinion of course.

  37. avatar Tom in PA says:

    Bootleg Pic-Mod

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