Rock River Arms XBT31521 LAR-BT3 | .308 Win | 20″ Bull

The Rock River Arms XBT31521 LAR-BT3 is a semi-automatic AR-style varmint rifle chambered in .308 / 7.62×51 NATO built around a 20-inch stainless steel bull barrel. It pairs a cryogenically treated 1:10-twist barrel with billet BT-3 receivers and a free-float M-LOK handguard to prioritize consistency and stability for precision work. For optics under $1,000 that suit this platform, a Vortex Crossfire II 3-9×40 provides a durable, clear variable-power option well matched to varmint and precision shooting applications.

Common uses include varmint hunting and precision target shooting, where the rifle’s heavy-profile barrel and two-stage trigger support sustained accuracy at extended ranges.

Product Specifications

• The manufacturer and model are Rock River Arms XBT31521 LAR-BT3 Varmint.
• The rifle is chambered in .308 / 7.62 NATO.
• The action is Semi-Auto.
• The barrel is a 20-inch stainless steel bull barrel that is cryogenically treated with a 1:10 twist.
• The magazine capacity is 20+1 rounds.
• The upper is a RRA BT-3 A4 billet upper and the lower is a RRA BT-3 billet lower.
• The rifle uses a rifle-length gas system with a low-profile gas block.
• The handguard is a 17-inch free-float M-LOK compatible rail.
• The trigger is a two-stage RRA match trigger.
• The pistol grip is a Hogue overmolded rubber grip.
• The finish on the receivers is blued/black alongside a stainless barrel.
• The overall length is 37.25 to 39.75 inches (stock positions).
• The unloaded weight is approximately 9.80 lbs.
• The rifling rate of twist is 1:10.
• UPC: 842834119752

This configuration emphasizes barrel rigidity and a stable mounting platform to enhance consistency for precision and varmint work. The heavy bull barrel and free-float M-LOK handguard support repeatable shot placement while the two-stage trigger gives a predictable break for longer-range shots. Overall, the XBT31521 is built for shooters who want a deliberate, accurate AR-pattern option in .308 that balances handling with accuracy potential.