1941 Winchester .303

[Bindi2]

Sapper 740
Its not the rifling its the erosion caused by the cordite which open based projectiles hide by bumping out to seal the barrel then sizing back down whilst moving down the barrel.
I am a F Class shooter ( 30 06 AI ) and have had a barrel fail on me when the gas beat the projectile to the rifling leaving the projectile pushing molten metal out the muzzle. The accuracy went south very quickly. 12 shots fired in that detail.