1 cold barrel
2 slighly warmed barrel
3 barrel now quite warm, shot wanders, and that can on the end holds all the heat from the gases right next to the barrel- vs letting them expell as the pill exits. Yes, they expell but not without some dwell time.
But I do not know anything just being a schmuck from the back 40.
button rifled barrels machined after bore formed will increase internal diameter if machined after bore work completed. cut rifled and hammer forged generally do not. Savage used to be all hammer forged, that may have changed. Krieger can be had button or cut. to the best of my limited knowledge.
a bit more thinking- free floated barrel? is still free after shot 2 with the can on?