If it has a crimp line around the bullet, I typically crimp it. If it doesn't I leave it alone. I've shot plenty of 223 through my AR's that didn't have a crimp, they are fine. The only time I crimp even without a crimp line is on a tube fed rifle like my Marlin 336. That is a bad time to have a bullet push back into the neck.
For "gas guns" such as the Garand, I do crimp. (nothing like blowing up a rifle due to a bullet collapsing into the case whilst cycling)
I wore out an old H'Day Three Prong Stab Crimp Die (pushed the case into the bullet 120 degrees apart...sort of like a "stake mark")
I now use an old LEE COLLET CRIMP.....
For those that do not crimp (and this is America...was a FREE COUNTRY, not so long ago) don't.
The caution with that is, it only takes one bullet stuck in the rifling, whilst unloading rifle during a (up to that moment) fine Hunting Caper with the resultant 57grains of POWDER dispersed LIBERALLY through the action of your rifle...to learn ya....
I crimp all my hunting ammo. 22-250, 30-06, 38-55 & 45/70... (I have had the stuck bullet in the rifling experience, whilst unloading rifle to get over fencing obstacle)
I have found (in several rifles in both the 22-250 & 30-06) that, for me, the crimped ammo tends to be a touch MORE ACCURATE with a smaller extreme spread on the chronograph.
With me, it all depends on how much neck tension there is (you can feel that when you seat a pill). For magnum rounds like 300 Win Mag and 338 Lapua I always crimp and I use a Lee Collet crimper for that.
Yeah. I worked up a load for my .308 with un-crimped cases. Think I might load up 25 crimped (Lee Factory Crimp die) and 25 un-crimped and do a comparison. If crimped shows improvement then I'll get a die for my .243.
I use friction fit on all my rifles except .223/5.556.........I use a Lee factory crimp on those......I've never had push back on any other the others including leaving them loaded in tubular magazines for long periods of time.
The issue with crimping any case is it work hardens the case mouth and that leads to shorter case life and eventual cracking and that includes straight wall pistol cases. Why I anneal all mine (including straight wall cases). Especially the heavy crimp ones like 44 mag and 460 Smith. I just anneal the ends back about 1/8".
I don't always crimp my reloaded ammunition; but, when I do, I use a taper crimp which mitigates any slight imperfections in case trim length. This works well w/ .45 ACP and just as well w/ common straight wall revolver rounds. I seldom crimp rifle loads since most of what I shoot are .03 and 03-A3 30-06 bolt action rifles. When I shoot handholds in my M-1 rifles, I use taper crimp. Have not ever had a problem with this method. Sincerely. bruce.
Like Texan, I only crimp if the bullet has a cannelure. However, I rarely use bullets with a cannelure. I only load three rifle cartridges, 300BLK, 7.62x51, and 6.5 Grendel. The Grendel and M1A only get match bullets, which typically don't have the cannelure.