I never crimp any of my rifle loads. I load .303 British, .308, and 7.62X39 and I've never had a problem with the bullet loose enough to move either in or out and not even with a semi auto. On one occasion I loaded 20 rnds. with the wrong powder and it took a few good whacks with the bullet puller to get the bullets out of the casings. As a quick check, I'll take the odd loaded round and give the bullet a firm push against the reloading bench. I've never had one move, so for whatever my 2 cents is worth, there it is.
Crimp all semi/full auto rounds,although .300wh is more of a kiss.No on bolt action...Use LEE FCD on ALL bottleneck rounds,for all of Lee's hot air,this is a very well thought out ,essential part of reloading.
I crimp all of mine like everyone else using a LEE FCD. The only one I won’t crimp anymore is for my 224 Valkyri, the 88 Gr bullets have plenty of bearing surface, there is no way these rounds would come loose.
Always, especially for the .30-30 Mod 94, but generally for every rifle caliber I load. I use the Lee FCD for all of them, though I won't use anything else made by Lee. Straight-walled calibers are a different matter, but I don't load any of those.
Ok, I have more time now....at 5:29 AM on a Sunday:
Those rifle cartridges that have the potential of being in the chamber for a series of shots from a different barrel always get crimped, such as my double rifles, combination guns or drillings. Under the recoil of repeated firing they can pull until the bullet hits the rifling. The British stake crimped those bullets and the Germans and American roll crimp them. Heavy cartridges always get a heavy crimp to aid ignition of heavy charges of slow burning powders.
Bolt rifles and single shots....well, that depends as well. GENERALLY I just turn the case mouth back against the bullet either in a crimp groove, cannelure or onto a driving band. If it is a cartridge/rifle combination where I've had to thin the necks below .008 to make a cast bullet/throat/groove diameter work I will crimp the bullet in place simply because neck tension has been so greatly reduced. I only have two bolt rifles I've had to do that with but, to fail to do so merely invites poor ignition.
To crimp or not to crimp? Well, it depends on several factors and it is incumbent upon the handloader to be cognizant of those factors.