Cut that baby! The loss in velocity is insignificant. I hear the 25-50 fps per inch often and its BS. 25 to 50 units is a huge "range" per inch. I've also read its 10 fps per inch, and that's BS too.
Every caliber will be affected differently but for the most part, the loss in velocity is not significant, up to a point.
For example, the 30-06 shot from a 28" barrel and 20" barrel, will have an insignificant difference in velocity for the purpose of a hunting rifle. Every inch shorter than the 20" length will have an increased loss per inch. A barrel length of 18.5" would be the minimum for the 30-06 before the loss starts to be significant.
I cut my 30-06 down to 18.5" and it shoots great, under 1/2" at 100 yards and without a noticeable loss in bullet drop from its previous 22" length. I shoot at distances up to 300 yards with this rifle. Our range only goes out to 300 yards so I don't shoot any farther but I'm thinking its time to bull-dose to the 400 yard mark!
Cut that barrel down to 20"!
Smitty