The fact that they will chamber is a good thing. If the shoulder were crushed badly, they wouldn't chamber. This is a common mistake for newbies who haven't yet discovered case trimming. Or as in this matter, set the seating die too low. Especially with .223 which doesn't have a very thick case.
I think what scares some people about this defect concerns what kind of rifle they are gonna be fired in. If it's a bolt action, it wouldn't be an issue so long as they chamber. However most AR design rifles have a floating firing pin. So if by chance you tried to chamber one that was more severely crushed that wouldn't go, there would be the chance that the firing pin could detonate the round out of battery. And who knows, in that batch of 400, there might've been one or two that had cases that were a teensy bit longer than the rest. And the couple of exceptions wouldn't chamber.
So what I've said above is a possibility, however slight. But if you chamber a normal round in an AR design, then extract it without firing, you will note a faint dimple in the primer where the firing pin bounced off of it. Without detonating the round. So it's obvious that there is some of this inherent to the original design.
My 5.56mm AR's have floating firing pins. Only my Armalite AR-10 in 7.62mm has a little spring on the firing pin that prevents it from floating.
Okay, suppose you go ahead and fire the ones that will chamber. The defect will be fire-formed out of the case which can be reused. So long as it doesn't have any other problems.
What somebody else said above, a cartridge headspace gauge is a nice reloading tool to have for checking your work.
For cartridges I'm gonna shoot in an AR (which is where most of my .224 bullets are used), if I have a bullet with a cannelure, that gets crimped. And these must have pretty uniform case length. For bullets without a cannelure, I only give them the gentlest taper crimp as a separate operation.
The RCBS die set that I use is specifically for 5.56mm, small base, and incorporates a taper crimp in the seating die. If you want to use it. As I said, I do it separately. Typically, I use a CH taper crimp die. But I've also got a Dillon taper crimp die that I like, seems like it has two facets to the taper.
belted too!
