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
If zombies, i have gone for big guns, will return soon !
if your here to take away my guns, please note you will be in range of said guns
current guns projects : Howa GK 1500, TM15 custom