Velocity Loss

[LocoGringo]

I've got an 18.5" Criterion barrel on my DPMS and am wondering what kind of velocity I might expect out of 175 grain ammo versus a 24" barrel.  Twist rates are the same and both are .308 versus 7.62x51. 

[imschur]

this might be helpful http://ballisticsbytheinch.com/ 

[Robocop1051]

From 18" to 24" you will only gain about 30 fps per inch, totaling 180-200 fps. That extra speed won't make a difference till you reach 800 yards.

There is a detailed post on here somewhere. I posted a rough velocity chart from 10" to 24".