Rock River Arms BT9 AR Pistol 4.5-inch barrel

Rock River Arms announced its BT9 9mm series all the way back in April 2019. The first two AR pistol models in the series featured 7- and 10.5-inch barrels. There was also a BT9 R9 Competition Rifle. They all accept Glock mags. Fast forward one year and Rock River just added a new AR pistol with a 4.5-inch barrel to the series.

Rock River Arms BT9 4.5-Inch Barrel AR Pistol Details

Outside of the 4.5-inch barrel, there are obviously a lot of similarities between the new variant and the first two AR pistols in the series. Firstly, like the other BT9s, the new 4.5-inch variant accepts Glock-style magazines. Rock River based the 4.5-inch variant on its billet aluminum lower receiver with a Glock magazine-compatible flared mag well. Also, like the other two, the 4.5-inch BT9 Pistol features the popular SBA3 Arm Brace from SB Tactical. It features a 5-position LOP adjustment.

Other similar features include Rock River’s over-molded A2 pistol grip and two-stage trigger. Beyond that is a winter-style trigger guard; it offers comfortable room for the trigger finger when wearing tactical or cold-weather gloves. The pistol also includes Rock River’s latest extruded aluminum upper receiver. Lastly, the 4.5-inch model comes standard with Rock River’s 4.25-inch pistol length lightweight free-float M-LOK-compatible handguard.

Now, onto the differences. One difference that stands out is the muzzle device. While the new variant features a chrome moly, 1:10 twist barrel like the others, Rock River opted for a Smith Vortex flash suppressor (1/2-36 threads) to top it off. For reference, the 7- and 10.5-inch variants features an A2 Flash Hider. Another difference, as expected, is overall length. The 7- and 10.5-inch variants feature an extended length of 26 and 29.5 inches, respectively. Do the math on the differences in barrel length and the new 4.5-inch variant has an extended length of just 23.5 inches; that’s nice and compact, just the way we like ’em.

The last difference is price. While the other two AR pistol variants have an MSRP of $1,250, the new 4.5-inch model has an MSRP of $1,350. For more information, please visit

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