Aftermarket Gas Blocks and Barrel Port Hole Alignment
You've decided to build your AR and got a nice aftermarket gas block, a barrel without the FSB pin cutouts, but now how do you align the block to the barrel's port hole, to know you're getting all the gas needed to operate the BCG.
Here's my little trick I use that's worked on all the AR's I've built. All gas blocks I've used have been steel, so if you use another metal alloy, use more caution when tightening down the block lock screws, as stripping is possible.
Once you have assembled the gas tube to the gas block, you slip the completed assembly onto the barrel and receiver hole position.
Now, if your gas block uses lock-down screws, install just one, but just barely snug it onto the barrel just enough to allow gas block movement with little resistance to help in alignment without being sloppy loose.
Grab a can of computer compressed air w/wand. You stick the can's air wand into the metal gas tube of gun. While one hand operates the compressed gas, the other hand will slowly rotate left to right and push/pull either front to back while listening to the air being blown through the tube. You'll hear the air either being cut off while turning one way or other and the sliding of gas block towards the barrel end or how far back to the barrel's gas block seat stop.
What you want is finding the best air flow given and once it's found you wrap your fingers around the gas block and barrel to keep aligned and remove the air supply. Then grab the hex screw tool and tighten down the 1(one) screw enough to hold everything in place.
Now look down from top at whole assembly. What you should see is the gas block, gas tube(if not bent), is everything in alignment with the centerbore of the barrel.
You'll find that all gas blocks have quite a bit of adjustable leeway for alignment before cutting off any air. Onto next step.
Get Charging Handle, BCG and slip into Receiver and watch how gas tube alignment and the BCG's gas key are interconnecting. There will be some slight resistance because gas tube has a small bulge just fractions from the tip that helps seal the gas key, but as long as the gas key and gas tube don't collide tip edges, but appear to slide within itself, you're GTG.
Get blue Loc-tite and install couple drops onto the 2nd(second) hex screw that was not installed. Now install and lock down tightly. Remove the first installed screw from gas block and put some Loc-tite onto it and lock down onto the barrel tightly.
You have now installed a gas block that allows all the gas it's capable of flowing to the BCG and you can now put on handguard or free float tube assembly.
Now, if the barrel's port hole is open to required size from the manufacturer, you know you'll always have enough gas, but this procedure still doesn't mean you don't tune your rifle for best effects of shooting, in that it still might require a heavier buffer, or using a heavier M16 Carrier over the slightly lighter AR15 semiauto Carrier, and testing all ammos for operation of what gun likes or doesn't like.
US Air Force 73-77
57th Munitions Maintenance Squadron F4 Phantom
Nellis AFB, Nevada
Life Member of NRA
CCW Permit Holder
Lifetime "Conservation Partner" Permit Holder