How To Install the SOLGW M89 Handguard

The M89 Drive Lock Rail from Sons of Liberty Gun Works brings new meaning to the old term "rock solid." It's a free-floating M-LOK® AR-15 handguard that is an outstandingly secure, versatile accessory mounting platform. The M89 is pretty easy to install IF you know a few tricks. Brownells Gun Tech™ Caleb Savant shows us how to do it step by step. SOLGW includes all the hardware you need, including the proprietary barrel nut that is the secret to the M89's remarkable stability. You'll need these TOOLS: barrel nut wrench that comes with each M89, bench vise, upper receiver vise block, hex wrench, 1/2" drive adjustable torque wrench, and a smaller 1/4" torque driver like the Brownells Magna-Tip® Adjustable Torque Handle.

 

PHASE 1: Put a little light grease like Brownells Action Lube Plus® on the barrel extension to help it slide into the receiver. Also apply a little grease to the receiver threads, then thread on the M89's barrel nut until it's hand tight. Tighten it down the rest of the way with the SOLGW barrel nut wrench motivated by the 1/2" torque driver set to 40 ft.-lbs. Then install the gas block and gas tube.

 

PHASE 2: Slide the M89 onto the barrel nut. If you're working with a Sons of Liberty Gun Works upper receiver, you'll find a little recess in the front of the receiver and a corresponding recess in the handguard. The little steel pin that comes with the M89 snugs into the recesses to ensure there's NO WAY the Drive Lock Rail can rotate on the barrel nut. If you have a non-SOLGW upper receiver, don't worry. The M89 also has robust anti-rotation tabs. If you really, really want to use the anti-rotation pin on your non-SOLGW upper, you can mill a hole in the receiver for it. CALEB'S WARNING: Do not try to drill the hole with a drill press or hand drill! Use a milling machine or take the receiver to a gunsmith who has one.

 

PHASE 3: Use the hex wrench to install the three nut-bolt-sleeve sets that clamp the M89 to the barrel nut. They squeeze the handguard around the barrel nut, while the shape of the barrel nut's outer surface causes them to pull the handguard back against the receiver. For extra security, use the small torque driver with a correct-size hex bit in it to tighten down the bolts with 25 to 30 in.-lbs. of torque. That's INCH pounds, not foot pounds. Your SOLGW M89 Drive Lock Rail M-LOK® handguard is now locked down tight on your AR-15!