Thread: Velocity loss in short barrel 308

Hey guys
Have just purchased a shortened 308 (17inches).
I am keen to make up a rough drop chart for it (very rough indication) and I will try and validate it as and when I can.
I don't reload, and dont have access to a chrono, so take the manufacturers data on the factory ammo boxes. From what I understand, the displayed FPS for 308 is based off a 24 inch barrel, what kind of approximate loss should I expect per inch, to roughly estimate my velocity from a 17inch barrel? I thought the collective forum mind might have a more accurate suggestion then google, as seems quite a range out there. I also know quite a few people have cut down 308s so might have some real world data.
Cheers!