Re: Lining up the gas block
Flip the block upside down- take the allen screw out (you'll notice the gas hole is drilled through one of the allen holes, and center the allen hole on the gas port hole. You'll notice that that leaves the gas block about 1/32" from the shoulder on the barrel. That's because they are made to be compatible with handguard retainers.
Well you probably won't be using one, but need to account for that space. Tighten the other set screw till it secures the block with the hole centered over the gas port. Now take some tape and loop it around the barrel to where it meets the block. That way when you flip the whole mess over you can touch the tape and know your front rear alignment is good.
flip the barrel over and dead center of the top of the gas block put a piece of tape lengthwise on the barrel as a witness mark for the hole recess location.
Now flip the gas block over, touch the tape for front rear alignment, allign the hole center axially with the tape running lengthwise, tighten one screw and dot the center of the hole with a sharpy, or tap it with a center punch.
Now put the other screw in, and remove the first so you can dot/or center punch the other hole if you want. Now remove the block, drill the recesses, and install the block with thread locker on the threads.
Done. Now you can install a gas tube, plug the barrel and blow to test gas flows through the port and tube.
How would a machinist do it? He would use a collet block to fixture the hole straight up- touching his (gas port size) drill bit dead center, set a vise stop, raise the quill, change drill bits, and flip the block over, touch off the vise stop, and sink the recess with a center drill, then use the horizontal way to move the required dimension to drill the other recess, but that's with a Bridgeport ($3500-$5500 used) and a collet block, vise and a shop. It's the right way, but it costs $5500 plus overhead for the shop. Trust me the tape will work, and it's the way to do it for $100 in your home with a drill press.
