Re: Input Please on SAVAGE 20" 300 WSM
I know of many such tests also.
Fact is, a 308 win. will even gain velocity with every inch as well and if I remember right, all the way to 36" were they stopped the test. The longest barrel thaey had. It was one that had more to gain from this as they concluded.
The test you refer to must have started out using a fast powder to begin with, not benifiting from the longer barrel much at all, therefore it still held velocity at 18".
Fact is if a real slow powder was used and the barrel shortend, the velocity will undoubtedly decay at the rate suggested, maybe more. If one switched to the faster burn powder it could gain it back to a point. When you get to 20" or less the likelyhood of gaining it all back are not good all while limiting your powder choices too.
I have a 20" 308 win. and a 18" 358 Norma Mag and they are handycapped in the order of 150 to 250 fps even with the faster powders.
These guys shooting the Ultras in 30+" barrels can all get velocities that you can't touch in the shorter 26" tubes so there will always be the velocity advantage in the longer tube.
You could have a short 18-20" tube with the WSM and still outdue the long tube 308WIN though. I would too stay with the long tube if hunting was the interest, if it were tactical, the 308 WIN would be it for sure.