in my 243 which has a 1;9 twist the accuracy will be fine if i sawed the barrell off to 9 inches and crowned it? or are we saying that there would be little noticeable improvement between 18.5 and 21.5 and 26 inches?
how far down the barrel does the burning powder go? I get quite a lot of muzzle flash from my short rifles if it is in the evening..... if it is still burning would it be better to use a faster powder in a shorter barrel and slower powder in long barrels like my parker hale?
My 458 has a 20" barrel and if I use 70gns of RL 19 40% will burn outside the barrel, with RL 7 which is very fast all will get burnt before the bullet leaves the barrel.
Find a mate with Quickload and they should be able to tell you.