I am a curious type and have intentionally tested various reloading related things like 50+ reloadings on same 9mm/40S&W cases, A-MERC vs other headstamp cases, shooting 10/15/20 year old reloads and firing loose primer pocket 9mm cases.
Like many, I mark and toss/recycle loose primer cases when I feel no resistance as primers are seated. Out of curiosity, I took a small batch of loose primer pocket 9mm cases and reloaded them 5 times with Winchester SP primers and W231/HP-38.
Result? They all went bang and did not notice anything on the breech wall face (I thought high pressure gas may leak due to loose primer pockets but I guess primer cup expanded to seal with the loose primer pockets).
- Would I still endorse using loose primer pocket cases? No
- Would it be the end of the world if some loose primer pocket cases got mixed in with other tight primer pocket cases? No
- Would I use loose primer pocket cases for match shooting? No
- Would I use loose primer pocket cases for range practice rounds? Sure, but I will mark them and toss/recycle on the next round of brass sorting.
You could consider using Wolf/Tula/Fiocchi SP primers with slightly larger cups to extend the life of loose primer pocket cases.
Resistance ... Resistance ... Nothing (even when bench priming) ... Resistance ... Resistance ...
Primers in loose primer pockets won't always fall out. If they do, the primer pockets were damaged/enlarged way beyond specs and I would toss/recycle the case right there.