Gas System
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The gas system takes gas from a port in the barrel back through the gas tube to cycle the action. You need a gas block sized for your barrel's journal (.750 inch is most common, .625 for pencil and some lightweight profiles) and a gas tube matching the barrel's gas system length: pistol, carbine, mid-length or rifle. Low-profile blocks fit under free-float handguards, and an adjustable gas block lets you tune the gas when you shoot suppressed.
Compare gas blocks and tubes below, and add them to your build so MyGunLab can check the size and length against your barrel.
Gas System: common questions
What size gas block do I need?
Match the barrel's gas block journal: usually .750 inch, .625 inch for pencil and lightweight profiles, or .936 inch for some heavy barrels. The barrel's listing gives the size.
Do I need an adjustable gas block?
It helps if you shoot suppressed or your rifle is overgassed: you can reduce the gas until it cycles reliably, with less recoil and less gas in your face. For a standard build a fixed block is simpler.
Set screw, clamp-on or pinned gas block?
Pinned blocks are the most secure, clamp-on blocks hold well without dimpling the barrel, and set-screw blocks are fine when the screws seat in dimples with high-temperature thread locker.