https://midstatefirearms.com/product/cheap-ass-750-steel-set-screw-ar15-barrel-dimpling-jig-v2/
shipping available
Want to dimple your ar15 barrel 180 degrees from the gas port but don’t want to waste money on a tool that costs a bunch of money? Use this instead! This no-frills gadget will help you figure out where to drill that dimple for your gas block set screw if you’ve got a barrel with no dimple.
It’s just a gas block with a hole drilled from the gas port through the top. Comes with a pointy set screw for centering on the gas port.
Step 1: slide it on the barrel.
Step 2: Center pointy screw on gas port and tighten
step 3: drill a shallow dimple through the gas block hole on opposite side of gas port (180 degrees from the gas port)
Simple as that! You only need one dimple, 180 degrees from the gas port, and it should work for any gas block. Virtually all set screw gas blocks have a set screw that is 180 degrees from the gas port.
note: you could maybe use this as an actual gas block, too.. but we wouldn’t necessarily recommend it.