Originally Posted by 25 Otter
All barrels with the exception of the better hand lapped blanks have a big and a small end.
I've slugged several factory 30 caliber barrels, including hammer forged, button rifled and broach rifled and none had smaller bore/groove diameters at the muzzle.
Even watched several broach rifled 7.62 NATO barrels made at the government arsenal in Springfield, MA, being air gauged for uniformity. They all were very uniform from the origin of the rifling all the way to the muzzle. While the groove diameter varied a few ten-thousandths between .3077" to .3082" across them individually, each one was uniform to .0001".
Maybe someone should explain to me how a rifling broach, button or hammer-forging mandrel can make a smaller diameter bore at the muzzle than at the breech end. Those tools stay the same size all the way through the barrel.