All things in the gas system should be in a state of balance, and generally on an stock Mil-Spec AR-15 direct impingement system, they are usually unbalanced.. Stock Mils-Spec setups are gluttonously over gassed in attempt to Sacrifice lighter, smoother Recoil for the guarantee of reliability. A direct impingement system works pretty simply; the round fires, the bullet travels down the barrel, pressure is leached off via a gas port (small hole) in the barrel which pushes gas up into a gas block, and the gas block reroutes the gas back down the gas tube and back into the BCG (bolt carrier group). That pressure presses on the bolt o-rings inside the carrier, which unlocks the bolt and cycles the action. Repeat until the magazine is empty
With that being said, an adjustable gas block can help with overgassed "large gas port" factory barrels by reducing gas that is used to cycle the action thus allowing for the following:
- Less recoil, results in a faster follow-up shot
- Less stress on the operating parts
- Less carbon build-up, better reliability and easier cleaning
All an adjustable gas block does, is adjust gas pressure just like a faucet does with water. Even by turning that gas pressure down significantly, most gas system are so over-gased that total reliability can still be had while delivering huge benefits to the shooter. The market has many options available that allow us to control gas pressure with Adjustable Gas Blocks like those from ERGO, SEEKINS, BLACK RAIN ORDNANCE, AND PATRIOT ORDNANCE FACTORY. Even further tuning can be Achieved By using even lighter weight Bolt Carrier Groups or heavier mass buffers and even springs, for even more for an amazingly light recoiling AR-15.
Enough Schooling, and now that you know.... Onward to fine tuning your gas block!
What you want to achieve is a rifle that functions correctly with the proper amount of gas pressure.
This is done by adjusting the amount of gas into the system. When this is done it should be with the actual load you plan on shooting. Too little pressure going through the system and the rifle will not be reliable and too much will cause excessive recoil and could damage your rifle.
The adjustments must be done in a safe area following all safety rules. “Make sure that the firearms if completely unloaded”
- I’m assuming that you have the gas block installed, properly aligned with the barrel gas port and the gas tube properly installed with the gas block tightened in place.
- Once this is done loosen the front set screw, then turn the adjustment screw on the side in until the screwstops (no not over tighten). This will restrict the gas to going to the gas tube all the way down.
- What you want to do now is shoot the rifle at a safe location in a safe direction with 1 round in the magazine.The round should fire and not lock the bolt back. This is because there is not enough gas to properly extract, eject and lock the bolt back.
- Now turn the adjustment screw 1 full turn out. Fire the rifle again with 1 round in the magazine. Continue this until the bolt locks open. Once it locks back this is the point where you have enough pressure to function the rifle.
- Now back the adjustment screw out 1/2 turn more, then tighten the front set screw. This will lock the adjustment screw in place.
- Now test the rifle with 10 rounds making sure it ejects and functions correctly and locks the bolt when empty.
You may be done now or you may need to allow a little more pressure. If you do adjust do so at ½ turn increments. Remember to loosen the front set screw first and re-tighten after.