280 AI with a 21" Barrel?

[brno375]

I have a Brno action that acquired a M70 barrel somewhere along it's life. It is currently chambered in 7x57 and I am considering having it reamed to 280 AI but the barrel is 21 inches. Will this hinder the new chambering? Do I estimate 50 fps for every inch of lost barrel length from published data? Eg A 160 gr @ 2900 fps with a 24" barrel would be 2750 fps out of my rifle? My Nosler manual shows 160 gr out of a 7x57 with a 22" barrel goes 2600 fps (so 2550 out of the Brno). 200 fps with a 160 gr is not that big of a deal to justify a rechambering, but I think 300-400 fps would be. The action was a little bubba'd otherwise I would put a new barrel on it. Maybe I just leave it and use it as a bushwacker. Opinions or insight?

 

[buckbrush]

I have measured Rem bulk 175 gr's at over 2900 fps out of my 21.5 " .280 ackley. In my expierience, you lose very little velocity with short barrels if you use heavy bullets for the calibre. Light bullets are a different matter!