Quick Tip: Mounting M-LOK Accessories Next to the Gas Block

An AR-15 gas block can literally live up to its name when it blocks you from mounting an accessory on your rifle's M-LOK® handguard. Brownells Gun Tech™ Caleb Savant explains what's going on when this happens and how to fix it. Let's say you're upgrading Old Trusty or building a new rifle with a full-length M-LOK® handguard that extends over a low-profile gas block. If you try to mount an accessory directly under or next to the gas block, you may not have enough clearance for the M-LOK® lock nuts between the inside of the handguard and the gas block. This is a common problem with those very slim, low-profile handguards that have become so popular.

 

If you go ahead and jam the lock nut into that space anyway, so it contacts both the inside of the handguard and the gas block, your rifle's accuracy WILL suffer. That's because the pressure on the gas block will cause the barrel to flex. This is what's going on if the rifle was shooting good groups before and suddenly doesn't after you install the new M-LOK® accessory. The fix is simple: reposition the accessory so the lock nuts don't touch the gas block and the barrel floats free. If you're mounting a bolt-on M1913 Picatinny rail, you might need to get a longer rail.

 

Look out for this: There could be enough clearance for the lock nut, but when you tighten the screw, the tip of the screw protrudes past the lock nut and pushes on the gas block. That'll trash the rifle's accuracy just as much as when the lock nut itself is the culprit. If you're really in a jam and MUST mount the accessory in that exact spot, grab a file, a stoning tool, or even a belt sander and grind down the screw tips so they don't protrude beyond the lock nut.