Is there a problem???

[DeanoBeanCounter]

:confused: I recently bought a 300 Win. Mag. by Steven's. I have been shooting factory loads, PMC 150 gr. J word bullets. I know backed out/flattened primers are a sign of over pressure. BUT, this is a magnum that operates at high pressure. So is this a normal thing with this rifle? I've shot 3 boxes so far and I think all the primers were flattened. Any comments? :???:
Deano

[The Double D]

Flattened primers mean nothing by themselves...PMC has a reputation for being "hot".

Try a different brand and see what happens.

[versifier]

Flattened primers are the first warning sign. When working up handloads, that's where you stop. If you have been testing in cold weather, back off before you shoot them in hot weather. When you see it with factory rounds, it means that you have ammo that is producing as much chamber pressure as your rifle can safely handle, as varying conditions might put the level over safe, as mentioned with regards to ambient temperature. It is not at all uncommon when shooting older rifles with new factory ammo to see similar pressure signs. To see it with a new rifle is not all that uncommon either, but it is disconcerting nevertheless. As long as you aren't seeing cratering or getting difficult extraction, it shouldn't be a big deal, (unless the owner happens to be one of those people who isn't happy unless he's got the biggest, fastest, etc., and you don't seem to be anything like that from your postings.) Just out of curiosity, I would also shoot one or two different brands to see what happens. If it happens with several kinds, it might warrant a letter to the manufacturer.

[9.3X62AL]

Could also mean slight headspace presence. A fully-formed shoulder from a fired case--NOT re-shortened in the sizer die--makes a better headspace reference than the belt on most belted nagnums. The 300 H&H and 375 H&H are a couple of the very few belted magnums in which the belt isn't a superfluous addition.

[buck1]

DIDO on the PMC. I wont even use Pmc brass, I throw it away. And for me that is a event!!...Buck

[Paul B]

Magnum cases are supposed to headspace on the belt. Take a dial caliper sometime and measure those belts. The dimensions on some I've checked out have been so sloppy that it's a miracle there wasn't a problem on the first firing. Chambers on belted magnum rifle can also be on the sloppy side. I get around all this by setting up my sizing die so that the round headspaces on the shoulder.
I've had ammo from Winchester in my .300 and .338 Win. Mags do the same thing.
Paul B.

[leftiye]

Try it again with fire formed cases with the cases neck sized only, as Al said.

Believe it or not it might only be excess headspace as was also previously said- due to cases with narrower belts than your rifle is chambered for. The primer backs out when fired. Then it is mashed flat when the pressure builds and the case head is pushed against the breech face. No high pressure needed in this scenario to produse flat primers. That is not to say that high pressure doesn't look almost the same- and it may actually be high pressure in your case.

Lots of factory loads flatten the heck out of primers. Factory loads are usually near max, and achieve velocities in most cases that we are hard pressed to egual in handloads (many use powders we can't get is one of the reasons).

So, try a proper pressure load in a properly neck sized case and see what that looks like. Chrono the load to be sure it gets the velocity that it is supposed to achieve (this says the pressures are in the ballpark they're supposed to be in). Use a load that you can get pressure data for in your handbook. Don't use a max load either just because it has pressure data. Not sayng that you would, just saying don't.

[AZ-Stew]

I agree on the headspace issue.

A chamber that's in tolerance, but at the "maximum" end of the tolerance range, combined with a particular lot of ammo that's on the "minimum" end of the tolerance range will create the condition described by leftiye.

Improper adjustment of sizing dies can create the same "minimum" condition in the ammo.

Regards,

Stew

[STP]

The PMC empties I find at my club show the same evidence. The same factory ammo shooters leave the empty boxes in the trash cans, but the casings are scattered on the ground.