Not sure I entirely agree with that statement. Many rifles will seat the bullet further into the case during recoil, which can lead to problems with pressure.george wrote:
Rifles (with the exception of some lever-actions), are usually not crimped.
This can be especially prevalent in magazine fed weapons, and of course the sharper the recoil, the more the possibility exists.
Load up the weapon and fire several rounds. Then take out the remaining rounds and measure the overall length. If it’s changed, then you need to crimp. If it doesn’t change, then that combination of primer, powder, bullet, shell, rifle, temp, and atmospheric conditions are fine. But change any of the variables and bullet movement could happen since chamber pressure could change and impact recoil.
My suggestion is play it safe…trim all rifle cases to the same size and crimp. If they’re trimmed to the same size, then the crimp die will give an accurate and repeatable crimp, and you won’t have to worry about bullet creep while shooting. Another benefit is repeatable pressures, which helps with accuracy.