Re: Loose primers
I've loaded thousands of rounds (223) for highpower service rifle comp. Just about everybody (except service teams) reloads due to cost, and most shy away from Fed brass for this reason, as others have noted. I've seen many a competitor get an alibi, and a call from center line "armorer to firing point xxx" at Camp Perry because Gold match blew a primer which lodged under the trigger or in the lugs. I know of one match at Parris Island where competitors could not bring ammo and were issued FGM by the match host, only to have the match called off during sitting rapid because of primers blowing out. Granted that may have been a hot batch that slipped out. When I'm loading on my Dillon I can feel a Federal case when one sneaks in - the primer goes in REAL EASY, and that case goes straight into the scrap can.
Also I've seen where a firing pin gets eroded from the hot gas escaping from a loose primer. Under a microscope it has chips and pits, like the moon. That firing pin caused me 3-4 pierced rounds (and resultant gas-eye) at 600 prone. Once this happens you have to toss it.
Hot loads make the pocket go loose faster, as you might expect. I never pick up USAMU brass! I 've seen them blow primers on a rare occasion, and be whacking the lower on the mat to dislodge it - and their primers are staked. LOL
Just my humble experience. Me no likey Federal brass, no.
Edit my friend Ray (high master, P100, owner of Ray-Vin shooting products) shot so much Fed brass, he took a dremel and cut a huge opening around the trigger in his lower so the loose primers would fall out. He called it his "primer ejection port". I kid you not. LOL