Toby,
I have been hunting with reloads in my bolt actions for the last 45 years and have never had a bullet slide from recoil (or anything else for that matter). A properly sized neck will hold a bullet verrry tightly.
During my immortal days, I reloaded for my .375 H&H, never crimped the bullets, and never had one move from recoil. Man I wish I had that pre' 64 Model 70 .375 now. I could probably trade it for an African hunt.