The Nosler reloading manual states NOT to crimp rifle shells except in specific instances. Crimping will increase pressures much higher than without and that could be very dangerous. Always follow the directions in the manual. Otherwise you place yourself and others at risk of harm or death.

I' ve never crimped any of my shells including my .40 handgun. I would check with the reloading books and follow what they recommend.

It all depends on how much neck tension you have on the bullet. With certain redding dies you can adjust this to really grip the bullet well to avoid slippage. I can get a 300 win mag with a 180 partition in place with sized cases from an RCBS die and push the bullet in almost too easily. In the case of any large magnum a crimp is necessary. Have you ever seen bullet tips after they get bashed in a magazine?