7.62MM AR Rifle Commonality


While browsing Brownells-ARFCOM tonight I ran across something worth taking notice of. Poster rpLo98 decided to rant a little on the AR10/SR25 ( 7.62MM) AR variants with some thoughts I agree with and have been saying since the 762 pattern started to get big around 09. His thoughts below.

JIMHO, and based on observations from sitting on the sidelines and watching multiple trainwrecks, if you’re going to assemble an AR-10 yourself, be prepared to invest some time with tinkering, analysis, research, and troubleshooting, and probably parts swapping. When I say AR-10, I’m not limiting the term to the true original Armalite AR-10, but the generic LR-308, AR-308, DPMS-type large-frame AR.

Even if you’re just slapping an assembled upper onto an assembled lower, even from the same vendor, there’s so many variables when it comes to AR-10’s, not to mention the lack of standardization, and the fact that AR-10 parts are still evolving, that there is a distinct probability that your home-assembled, home-built AR-10 may not run smoothly from the get-go. remember: if you ASS-U-ME, …

This is especially exacerbated if you’re going economy-grade with the idea that you’re going to save yourself a few bucks because you’ve done an AR-15: not the case. The dollars that you thought you were saving are invested in time and perhaps parts.

variables which affect functioning include:
ammo selection
buffer weight
buffer spring
buffer tube
gas length
barrel length
gas port
bolt carrier shape
recently, bolt carrier gas ports
source of forward assist (some AR-15 FAs don’t work on AR-308s)
location of forward assist on receiver
gas tube standard
head space
firing pin
pivot/take-down pins
mag release
DPMS or Armalite barrel nut
one vendors DPMS-type AR-308 upper might not fit another vendor’s DPMS-type lower
receiver rail height
suppressed or not
probably at least a dozen other factors,

not to mention:
AR-specific tools
home-assembler quality of assembly
home-assembler knowledge
home-assembler patience.

even if you buy an assembled lower, or even just a buffer tube kit, the vendor has no idea if you’re putting this on a 7″ pistol, or a 24″ long-gun, let alone what gas length or gas port your randomly selected barrel has, not to mention your ammo selection. one size does not fit all.

My humble opinion is that this applies to all brands of large-frame AR “kits”, parts, and assemblies.

like i said, JMHO. YMMV

I know this seems obvious but it’s not to a lot of people. The fact is there is no standardization of the 762 guns like there is the AR15 even with military adoption. There is thankfully and finally more widespread use of the SR25 pattern magazine. Not the M14 magazine patter used by “Armalite” for a while. The Colt 901, the M110 from KAC ( obviously) the LMT , the Larue all use the SR25 pattern magazine. And with that came the very good and very affordable 762Pmag from Magpul. Everything else is iffy.

There are some parts that will work with a couple of makers 762 guns but not many. And the thing to remember beyond the idea of putting one together yourself, which I would never recommend you doing with a 762 gun at this point, is that the makers themselves still haven’t quite got all the bugs and kinks worked out of the 762 guns. KAC would not admit it, but they are constantly tweaking the SR25s. Not because of better things coming along, but to get them to work better than past models. The problems with the M110 sniper rifle are well known. They even made a lot of back pedaling on that one, First it was to replace the M24 , then ” oh no no it was never meant to replace the bolt gun, it was meant to be a DMR replacement”. Then it was so telling us it has the same firing schedule as a bolt gun… It’s a fine gun but the truth is, it was a long way from being a mature design.

The cheaper bargain companies.. nuff said..

The fact is, we do not have the abundance of parts with commonality like we do with the AR15 yet. Every maker has at one point tried their hand at their own specs. For reasons that should be obvious. Those Fat Gov Contracts!!! Which is fine. But until something changes and one companies pattern is widely adopted and the other companies follow, we are still a ways from that. If you still want to go your own path at the very least make sure the gun you choose takes the SR25 pattern magazine.


  1. I’m sorta in the market for a large-pattern AR in 6.5 CM. I put together a budget AR-15 a couple of years ago and did a little research on doing it again for my 6.5. And I pretty much wound up in the same place you did: yeah, no thanks.

    I’m not ready to buy yet, but so far I like the Savage MSR10 Hunter the best.

      • Thanks for the tip on the Colts in 6.5. I can’t find a Colt that’s in the same weight range as the Savage. The 901 is 8.4# to Savage’s 8#, and the 6.5 that Colt has on their web site is a full 9#. It looks like Colt is using a relatively heavy barrel profile, which is the opposite of what I’m looking for in a field gun.

  2. If you think working on a AR-10/etc 7.62 AR platform is hair-pulling, try working on a BM-59. No overall manual or drawings in English, a sometimes bizarre selection of parts, a couple of variants that aren’t really compatible with each other, and then a bunch of people attempting to fit Garand parts to the BM-59 because “it’s what they had laying around.”

    Lots of fun.


Please enter your comment!
Please enter your name here