Flattened primers has long been one of the first "regular pressure signs" that reloaders can use to keep their reloads within safe limitations. And it is one that I frequently use personaly. Ive noticed many members consider it unreliable. My question is has anyone with a strain gage done any testing to see if there is a uniform pressure at which a given primer will begin to flatten? If so I would be very intrested in what the results may be.

Interior ballistics what a web we weave consider Item #5
http://www.frfrogspad.com/intballi.htm

Just how flattened a primer will appear will vary tremendously with how much headspace a given cartridge has in the chamber. The more headspace, the flatter the primer. I won't go into the mechanics of how this occurs, but it is only when headspace is reduced to virtually zero (neck-sized brass previously fired in the same chamber) that a comparison of primers will give any indication of relative pressure. Even then, flattening will somewhat depend on the brand of primer and how hard/thick its cup is.

quote:

Originally posted by Stonecreek:
Just how flattened a primer will appear will vary tremendously with how much headspace a given cartridge has in the chamber. The more headspace, the flatter the primer. I won't go into the mechanics of how this occurs, but it is only when headspace is reduced to virtually zero (neck-sized brass previously fired in the same chamber) that a comparison of primers will give any indication of relative pressure. Even then, flattening will somewhat depend on the brand of primer and how hard/thick its cup is.

Exactly.
And to take it one step further, you can have flattened primers without having excessive chamber pressures BUT you will not have excessive chamber pressure without having flattened primers.
Wouldn't you agree?

Ummmm. . . mostly. You could theoretically have some primers with very hard/thick cups which wouldn't flatten substantially even though pressure was high enough to cause unsustainable case head expansion. Of course this is speaking of a high intensity cartridge. With a cartridge with lower working pressures like a .22 Hornet or .45-70 you could easily exceed safe working pressures without flattening primers.

What makes you think the Hornet is a lower pressure cartridge? Then can run just under 50K. the new 17 Hornet runs fairly hot.

I feel primers are a piss poor method for determining if pressure is over max. Besides having pressure measuring equipment a chronograph and micrometer are all we really have to go by, add difficulty opening the action. Throw in a factory round for comparison.

My 7RM used to flatten every primer (and I only could get 3 loadings on the cases). Once I learned to set my sizing die to just set the shoulder back 2-3 thousandths my primers started to look perfect and I found I could get more loadings on the cases - all with the same load. So, while a flattened primer can indicate excessive pressure is doesn't always mean excessive pressure. I find a sticky (or obviously stiff) bolt lift, ejector marks on the case head, or hard extraction to be my "regular pressure signs". Loose primer pockets are also a dead giveaway to a load that probably should be backed off a little.

quote:

What makes you think the Hornet is a lower pressure cartridge? Then can run just under 50K. the new 17 Hornet runs fairly hot.

Well, SAAMI specs would be the short answer.

But anyone who has ever worked with the Hornet case will appreciate that its foil-thin brass is in no way designed to contain pressures upward of 50,000 psi. Heads will expand and unsupported sidewalls just in front of the rim will blow out at pressures approaching 50K.

Prime a Hornet case with a good, tough magnum SR primer and you'll never be able to flatten it before springing a leak in the case itself.

quote:

Originally posted by Stonecreek:


Prime a Hornet case with a good, tough magnum SR primer and you'll never be able to flatten it before springing a leak in the case itself.

Interesting. I've shot a few when I was a kid but never loaded for one.

"Flattened primers" used to mean something when they were CONVEX to start with (IIRC Rem primers were convex & Win primers were flat back than), but now that they are FLAT TO START WITH it doesn't mean much at all.

When reading primers, and beating open bolts, was all we had to work with (IE: back when each re-loader developed their own data because the only "book" data was by Sharpe and Ackley) Rem primers were the #1 choice for development work BECAUSE of there shape.

BTW, I still have the original 4 primer punches that came with my first RCBS press, large and small FLAT, large and small CONCAVE (to go with the convex primers).

Lots of good input.. Ive never had a 22 hornet but I do have a 45-70. I use Lever gun data in a Buffalo Classic action which contains rounds like 280 Rem and 308 so I dont worry to much about excessive pressure with that one.

Most of my other cases run from about 46,000 to 52,000 CUP and primer flatening seems to coincide with my listed Max data most of the time. By flattening I mean when the edge of the primer begins to fill the primer pocket to the edge. I dont worry to much about that, but if I start to get cratered primers, which is practicly never, then I get concerned. In other words I stop immediatly and back it off.

But I can appreciate what you guys are saying about varrying circumstances causing different flattening or not situations. It makes sense.

Still would like to see some actual data involving pressure equipment reguarding specific cases and specific primers though.. I think it could be informative.

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Originally posted by Wstrnhuntr:
Still would like to see some actual data involving pressure equipment reguarding specific cases and specific primers though.. I think it could be informative.

Lots of luck getting that data unless you wish to purchase pressure measuring equipment and do it yourself. The various companies making primers and powder have no reason to compile such data.

While I would agree that primer signs of pressure can vary with the gun and primer used, I have found inspection of primers very useful over the years in determining pressure levels of loads. Inspecting primers is only useful in guns with strong actions as in guns built for lower pressures you won't get primer signs of excess pressure until you've dangerously exceeded the pressure the gun was made to take.

Wstrnhuntr, FWIW, I have a couple of M-70s that will produce flattened-cratered primers prior to other signs. I agree with you and others that those cratered primers are a early warning but in a action like a USRA/FN M-70 or a M-700 I still look for the harder bolt lift and sticky case extraction, and marks left on the case face as the real deal.
I have always heard that Winchesters were notorious for oversized holes around the firing pin and that seems to bear some truth.

Flattened primers use to freak me out, but I've seen so many flattened primers with factory loads and minimum charge reloads that I know it's not reliable. If I start to see it molding up around where the firing pin hits, or see other pressure signs, then I start worrying

quote:

Originally posted by Stonecreek:
Just how flattened a primer will appear will vary tremendously with how much headspace a given cartridge has in the chamber. The more headspace, the flatter the primer. I won't go into the mechanics of how this occurs, but it is only when headspace is reduced to virtually zero (neck-sized brass previously fired in the same chamber) that a comparison of primers will give any indication of relative pressure. Even then, flattening will somewhat depend on the brand of primer and how hard/thick its cup is.

Agree 100%