The KAK Multi Position Barrel Dimple Drilling Jig is great for perfectly aligning dimples for your AR-15 barrel. The Drilling Jig is constructed from 4140 hardened steel with a mag phosphate finish. The Drilling Jig is designed specifically for gas block set screw spacing of .400, .425, .450, .470, and .500.
Here are a few that we have measured:
Don't worry, just do the following (see photo):
Note: Potomac Armory has learned that, if you're doing a lot of drilling and your KEO Brand Spot Drill gets dull, you may want to opt for a standard 1/8th inch hard metal drill bit, in combination, with the EZ Accuracy Gas Block Dimple Tool.