Quick Tip: What's the Best Barrel Length for an AR-15?
4,286How important is barrel length? Many AR-15 fans have been asking that, 'specially since 13.7" barrels have become so popular. Brownells Gun Techs™ Steve and Caleb are here to sort it out for us, starting with the big question: Do you really need anything other than a 16" carbine barrel? Sweet 16" is still the do-all AR-15 barrel length, says Caleb, because it'll work well with a wide variety of bullet weights. A 13.7" barrel works great with the common 55 grain and 62 grain bullets. But it may not deliver the full potential of heavier or lighter bullets.
Short, compact AR-15s are the hot ticket for competition and personal-defense right now, and a 13.7" barrel fills the bill nicely. You do have to permanently pin a muzzle device to it, so you get the overall length up to 16", unless you fill out the ATF application and pay $200 to get the SBR (short-barreled rifle) tax stamp. Plenty of flash suppressors, compensators, and muzzle brakes out there are long enough to meet the 16" minimum. Bonus: the 13.7" barrel shifts the rifle's balance point back toward the center of the gun so it's not front-heavy.
What's the difference in bullet velocity between a 13.7" and 16" barrel? With a 55-grain bullet, the difference in muzzle velocity is minimal, unless you're shooting at very long range. Caleb gets excellent accuracy at 500 yards from his 13.7" barreled rifle. Going shorter causes problems. There's a dramatic DECREASE in muzzle velocity with 5.56 / .223 ammo in barrels shorter than 10.5". The gas system also gets more finicky with sub-10.5" barrel lengths, so reliability may go down.
Does a 20" to 24" barrel get you any benefits? The extra length doesn't really improve bullet velocity. Caleb's Rule of Thumb: you'll get the best performance with standard 55 and 62 grain bullets, as well as lighter and heavier bullets, with an 18" barrel. If you're firing more than a few shots, a shorter, thicker barrel is actually BETTER than a long, skinny barrel, which heats up faster and has more barrel whip, causing your groups open up!
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