The thread specifications for the AR-10 barrel nut are 1-7/16” and 18 TPI-3A. The original AR-10 was developed in the 1950’s by ArmaLite, who still owns the AR-10 trademark and sells the only rifle officially called the AR-10.ĪrmaLite AR-10 rifles use their own proprietary barrel nut standard which is incompatible with most AR-10/308 derivative rifle models on the market. The family of rifles generally referred to as 'AR-10's or 'AR-308's encompasses a variety of rifles from a variety of manufacturers. Although similar in appearance and function, different rifles may have different upper receiver designs with parts that may or may not be interchangeable. This situation makes shopping for a free float quad rail or handguard a bit complicated.ĪR-10 style rifles have a few different commonly used barrel nut designs (the attachment point for a free float handguard), each of which is compatible only with a free float quad rail or handguard built specifically for that design. The two most common standards are for the original AR-10 and for the DPMS LR-308. Both of these standards are now used by a number of different manufacturers. What is the difference between an AR-10/LR-308?

Bcm 10 inch quad rail