There is much confusion about the effects of these short barrels on velocity. It makes sense that a shorter barrel will produce lower velocity, but how much less? Since the Army rolled out the 14.5 inch barrelled M-4 in 1992, there have been a lot of people shooting shorter barrels. The SEALs developed the Mk18 with a 10.3 inch barrel and many military and law enforcement units have gone short. AR pistols have brought shorter barrels to the common man.
Over the last year or so, Eagle_19er posting on AR15.com has gathered forty-one different factory loads and tested 10 rounds of each in a 10.5″, 11.5″, 12.5″ and 14.5″ barrels to establish a baseline velocities. They run the gamut from 55gr Wolf Polyformance steel case to a few flavors of heavy OTM loads.
It’s by no means an exhaustive list of everything available in 5.56, but these loads cover many of the popular “off the shelf” (and a few more obscure) loads that many of us shoot at the range and/or depend on for self defense, hunting or duty.
You can see all of Eagle_19er’s work on AR15.com: Suppressed 5.56 SBR Velocity Tests–41 Factory Loads from 10.5″, 11.5″, 12.5″ & 14.5″ ALL DONE