guesstimate

[M1NM]

Is there a formula to convert the fps out of a 24" barrel into the likely fps one could expect from a 20" barrel?
Want to make up some 223 match type ammo and noticed that Hornady 75 grain is going 2790 fps out of a 24" barrel. I've got a 20" barrel and wondered what I should aim for in fps.

[StratORcaster]

I read that you can expect about 50 less fps per inch, so ~ 200 less?

[J-cat]

I vote 50FPS per inch.