Scrap the brass if gas leaks past the primer on firing. A test would be, place a primer on the reloading bench. Take the brass in you hand and try to seat the primer with hand pressure. This will give you an idea if pocket is too loose.
Good advice.
If you are reloading for semi autos you do not want the primer falling out due to inertia. It will cause a malfunction.
When a primer falls out of a case by itself that is bad.
I pick up range brass and I picked up a handful of 45 ACP AMERC cases. These turned out to the worst made brass I have ever owned.
I load on a Dillon 550B and it is difficult to determine primer seating pressure unless the primer is grossly over sized.
So I would go to the range and load up my magazines with my reloads and every so often I would find an AMERC case with no primer. Digging through the ammo can I would find the primer and some spilled powder. The powder was coming out through the exposed primer hole.
On a number of these cases I decided to see what would happen if I pushed the primer in with my thumb, put the case in the chamber and fired it.
I did not get primer leaks but you have to understand that the powder charge had decreased by some unknown quantity, and 45 ACP’s are not high pressure at all.
I had primers come out of AMERC cases during feed, the pistol would go click, extract the case, no primer. Once I found the primer at my feet.
Overall I consider it poor practice to have primers that fall out and it is possible that loose primers in high pressure ammunition could leak and etch your bolt face.
These are pictures of AMU and USMC rifle team brass. Stuff I picked up at the 600 yard line at Camp Perry from the AMU and USMC shooters I was with.
This is over pressure, as you can see from the gas leaks. Some of this brass, if you turned it base down, the primer would fall out.
I would not reuse this brass, it is fit only for scrap.
AMU
USMC