well as i stated above to reach max velocity the barrel needs a max length on 22, any other length for (30 odd 6, .308 or similar rounds) will just reduce velocity and create drag down the barrel on the bullet and reduce the gas pressure on the bullet while it travels along the barrel(this is easily looked up on the net)
now the problem of doing this is it takes the "historic" quality away.(i personally dont give a darn there are millions of these things)
its just another way to improve accuracy a bit
Owner of the 91/30 mosin nagant: Black Lightning
"if zombies, i have gone to get big guns, be back soon!"