These days everyone builds their own AR and for good reason…its a ton of fun, can save you money and gives you good knowledge of how an AR works. One issue that many AR builders run into is finding compatibility issues with the parts they bought. With the popularity of ultra low profile handguards one of the most common issues is gas block incompatibility. Many handguards are so low profile that they can actually come in contact with the gas block itself or accessories attached to the handguard. I recently ran into this issue myself and figured I would share my experience with you.
One of my most recent builds is a DMR style rifle with a BSF Barrels 16″ barrel with a Carbon Fiber Shroud. Because of the carbon fiber shroud (designed to strengthen the barrel, reduce weight and help it vent heat) the gas block seat is .936″ so of course I just ordered any old .936″ low pro gas block.
Everything installed just fine, I slid the Cross Machine Tool UHPR Mod 2 handguard over the barrel, tightened it all down and … DUN DUN DUUUUN … the gas block was touching the bottom of the handguard. Not just close, literally touching. That’s called “unfreefloating” your barrel. 😂😂 This is something I verify every time I build a rifle as I’ve also seen MLOK screws touching gas blocks as well. Anything coming in contact with the gas block / barrel can and will effect accuracy even at just 100 yards.
In a basic beater build you might not care but in a build like this where accuracy is the goal, you have no other choice than to either swap out the gas block or swap out the handguard. Easiest and cheapest is to swap the gas block. Thankfully Cross Machine Tool has just released their new line of J.A.G. (Just A GasBlock) gas blocks which includes a .936 Gas Block specifically designed to fit under their UHPR handguards and many other super low profile handguards.
**One of the only things I actually do like about .936 gas block seats is that the .936″ opening of the gas block is usually big enough to remove without taking off the muzzle device**
While I had the gas block off I also decided to put a second dimple on the barrel so that the second set screw of the gas block would screw all the way in instead of sticking out just to make sure there was adequate clearance.
At this point it was time to reinstall the CMT handguard and check to see how it fit. Flipped it over and definitely good to go! The new Cross Machine Tool JAG .936 Gas Block did the trick and my barrel is now truly Free Floating.
Only thing left to do now is get this blaster to the range. I’ll have a full review of the BSF Barrels 16″ barrel coming soon. If you’re looking for an affordable low profile gas block you can’t go wrong with the new Cross Machine Tool JAG Gas Blocks.