This guide will help you choose an AR 15 barrel for an upgrade or buy for a new build. This video covers barrel length, twist rate, and gas system length. Part 2 covers muzzle device choice, round lethality / range, barrel material, and chambers.
The most common AR-15 barrel lengths are 14.5", 16", 18", and 20". I prefer 18", or 16" for maximum velocity without excessive length or weight. 14.5" barrels have legal concerns and must have a pinned flash hider, compensator, or muzzle break, which I do not recommend. 14.5" guns also don't have enough velocity IMO, especially for 5.56 NATO.
Barrel Twist rates:
1 in 7 (1:7), 1 in 8 (1:8), 1 in 9 (1:9) are all discussed. A shorter twist rate, 1:7 provides the most aggressive twist allowing the heaviest bullets (77 grains) to be effectively stabilized. 1:9 works with 55 and 62 grain bullets, but should go beyond there. 1:8 works with 55-68 and some people use 77 grains. Excessive twist can negatively affect very light bullet accuracy and insufficient twist will not stabilize heavier bullets.
Gas system length.
The three common AR15 gas system lengths are carbine, mid, and rifle length. I do not recommend carbine length gas systems with 5.56 since it provides no real benefit and I find the ergonomics poor. A mid length gas system is best for a 16" barrel since it makes the gun easier to shoot and handle. The longer gas system typically also has a longer handguard, improving ergonomics. For a 18" or 20" barrel gun you want a rifle length gas system. This will be very easy to shoot, provide a very long hand guard gripping surface, and generally be awesome.
I said gas pressures increase over barrel length, which is incorrect. Gas pressures are highest in the chamber and decrease over time/distance. The bullet does still pickup velocity with longer barrels, but the pressure slowly decreases.
However, the advice given still stands. Longer gas systems are often softer shooting and generally regarded as more reliable. I just explained that part really wrong.
AR 15 Guide Playlist:
Check out my AR15 Scope Video here:
Vortex Viper PST 1-4x24 Scope Review:
How to Choose a 3 Gun Pistol:
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