In the last blog post, I had installed the front gas block and was getting ready to cross drill and pin it in place. I mentioned that I’d use the original factory barrel stub to determine the size hole I’d drill for the gas port.
Wow. A number #15 drill bit is the one that fits the original port. That’s .180” and in my opinion is probably a bit too large. A port this size would more than likely over gas’s the gun and cause the bolt carrier to slam into the rear trunnion. This in turn could easily cause premature wear to the receiver. A quick search for AK gas port specs turned up sizes all over the spectrum from .128” all the way up to .180”. I’m pretty sure the Yugoslavian factory chose this larger size for a couple of reasons. First off, they were perhaps taking into account the carbon fouling and dirt build up of firing hundreds of rounds by their military. Secondly, there’s the spindle valve for the gas cut off for the grenade launcher. I’m pretty certain they wanted to ensure there was enough gas from the grenade cartridge to get the grenade off the end of the muzzle. But you see, we’re building a sporting rifle, not a weapon of war. Since there will be no grenades fired off this gun file’s muzzle, I’m thinking in terms of longevity. Instead of drilling the gas port out to .180”, I went down a few drill sizes and made the port diameter .161” using a size 20 drill. If the rifle doesn’t function, it’s easier to go back and redrill it to a slightly larger size.
Once the gas block is drill and pinned, I can now drill out the gas block. This way I know the gas block won’t slip out of position.
It looks like an awkward angle, but I’m able to get the gas port drilled at the proper angle. Things will go pretty quickly from this point.