I guess I left one thing out. On a .308 that measurement is from groove to groove. The .303 on the other hand is from land to land and the grooves are suppose to be .005 to .0055. So if you work it out the correct bullet size should be .313 or .314 depending on what size the barrel made it to. The normal .303 bullet is .311. So what I guess I'm gettin at is having a tighter fitting bullet in the bore will that seal better and raise combustion pressure? Or do you think that the .311 bullet grows enough to seal properly?