Here is a decent article with pictures for you Robin:
Crimped primers come from the military side of things – it helps to hold the primer in when headspace is deliberately loose or just got that way. Military ammo can get a rough ride and anything to hold it together – from crimps to tar bullet seals – helps.
But you find it in civvy ammo too – “NT” ammo, and just ammo.
The old primers push out, maybe reluctantly, then the new ones don’t want to go in. So you have to get the crimp out. But how? What’s the Best way?
Crimped Primer 5.56 NATO
Crimped, Primer out
Crimped primer, staked instead of circled
Primer Pocket types
Here are the ways I know of. Where you see “ihui”, it means “I Have Used It” – all else is gleaned from the web and talking to / observing fellow reloaders.
……………………….Rest on linked site…………………..
Hope that helps.