Is there any muzzle velocity advantage in having a 24" barrel vs the standard 20" versions. From previous posts, several from Troy, I understand that accuracy is not the issue between a 16" and a 20" but velocity is. I have a 24" Bushmaster V-Match upper but was considering switching to a standard 20" because of size/weight. Will I lose a lot of velocity by losing 4" of barrel or is the powder completely burned and no gain is acheived with the longer barrel? Will losing the free float barrel affect accuracy dramatically?  I already have a 14.5" and 16" barrels for smaller "Fighting" versions of the AR so no posts about the advantages of these lenghts are necessary.

[img]http://www.bushmaster.com/images/faqchart.gif[/img]

From Bushmaster's technical data.

Mike

As the chart tacked up by mr_wilson shows you will loose a bit of velocity.  And as Troy states, it depends on what you want to do with the rifle.

That being said, the only reason I would own a 24" barreled AR15 would be for a dedicated varmint rifle. That length seem to big and heavy for me.  I have a 16" bull barrel scoped and floated AR15 that shoots fabulous.  I also have a 26" barreled bolt ation rifle in 220 Swift that is my long range varmint rig.  A 24" AR15 with the right ammo would be a good compromise.  Since you have two short AR's, keep the 24" as is.