What AR15 5.56 parts are compatible with the .308 AR10?
A number of AR15 parts fit and work perfectly in the AR10 .308 platform. There are a few key differences and this article seeks to clarify some of them. While there is only one standard Milspec AR15 platform (although some manufacturers make proprietary billet uppers that will not fit every handguard), the .308 AR10 platform has 4 common platform standards. These standards are Older original LR308 DPMS High Profile HP (Smith & Wesson S&W and Mega use this), Newer LR308 DPMS Low Profile LP, DPMS GII (small frame, very similar in size to AR15), and Armalite. To find out if you have a newer model or older DPMS pattern receiver, the easiest way to measure is with a caliper or ruler the "tang" at rear of receiver. This is the nub above the charging handle. The newer version LP measure 1/8" and the old version are 3/16" thick.
Lower Parts Kit LPK
Most of the Lower Parts Kit parts are compatible with a few exceptions. The triggers are compatible and you can use any of our AR15 trigger upgrades on the AR10 platform. The DIFFERENT AR10 parts are:
- Takedown Pin (longer in AR10)
- Receiver Pivot Pin (longer in AR10)
- Bolt Catch (beefier in AR10)
- Bolt Catch Pin (threaded in AR10)
Receiver Tubes (Extensions)
The A2 fixed tube (no machined positional holes in the bottom) may be used for both the AR15 and AR .308. The AR .308 does use a DIFFERENT fixed length buffer and spring than the AR15. The collapsible tubes (generally have 4, 5, or 6 positions milled into the bottom) fall into general categories of Mil-spec 1.15" diameter or Commercial 1.17" diameter. However, there is a third collapsible tube that is slightly longer at 7-7/8" (3/4" deeper spring chamber): Armalite AR10 Carbine Mil-spec Diameter (I sell one such tube kit that is USA made by UTG Pro ). All Mil-spec or Commercial tubes are threaded the same and BOTH will fit the AR15 and AR .308 receivers. All the collapsible tubes also use the same castle nut and locking plates (these two parts are unnecessary with fixed tubes). Similarly to the fixed tube scenario, the AR .308 and AR15 platforms require DIFFERENT buffers and springs for the collapsible tubes. There are therefore 5 completely different spring/buffer combinations that are generally sold: AR .308 fixed, AR15 fixed, AR .308 collapsible, Armalite AR10 collapsible, AR15 collapsible. These 5 combinations cover basic build scenarios. I have seen .308 builders use the Armalite AR10 collapsible and AR .308 collapsible sets interchangeably without issue (they both use the same buffer/spring) but I would recommend going with the one suggested by the upper manufacturer. There are a ton of variable weight spring and buffer aftermarket items available for tuning your rifle if/when problems with cycling arise. These include H, H2, and H3 weight buffers as well as stiffer or softer springs. Another possible solution for cycling issues that is easier is to tweek is an adjustable gas block. This solution will allow you to stay with the appropriate basic 4 buffer/spring sets (as previously described) and then tune out any problems out with the gas amount.
- AR collapsible tube (milspec or commercial) with AR15 collapsible buffer/spring
- AR collapsible tube (milspec or commercial) with AR10 collapsible buffer/spring
- Armalite AR10 collapsible tube (milspec) with AR10 collapsible buffer/spring
- A2 fixed tube with AR15 fixed buffer/spring
- A2 fixed tube with AR10 fixed buffer/spring
Upper Receiver Parts
Most AR10 parts are different than AR15. The forward assist is the same for both AR15 and AR10. The DIFFERENT AR10 parts are:
- Dust Cover (AR10 Ejection port cover is longer)
- Charging Handle (AR10 handle is longer) **THERE ARE SEVERAL CHARGING HANDLES MADE FOR 308 THAT WILL NOT WORK WITH EVERY 308 RIFLE. MAKE SURE YOU ARE COMPATIBLE BEFORE BUYING UNLESS YOU ARE OPEN TO MODIFYING THE PART.**
- Bolt Carrier Group (Larger than AR15)