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The primers were indented at times, and sometimes pushed flat, and blew out three or four times.

The webs of the blown cases were far out of specs.

The chronograph speeds showed now signs of pressure. I got 2330fps from 36.5gr S335.

If the primer is not supported about instantly when firing, it will jump out, usually piercing the primer, are the ejected primers pierced or deeper indented?

Initially you spoke of  huge head space ? Go read the GS Custom test method for head space on bolt closing using the tape method.

Janfred, we pulled two of the guilty cartridges and the loads were on spec.

We also fired two others after weighing them, and their speeds were on spec as well.

It looks like high pressure, but there is nothing to cause it. If we missed something that could have caused the overpressure I would be delighted to know about it!

New brass usually has a much smaller base-to-shoulder dimension than fire-formed. If your theory is that excessive headspace causes blown primers, then you should be getting blown primers with factory ammunition and loaded new brass.

A stuck bolt and a blown primer are the classic signs of overpressure. To be sure, check for ejector marks or smears on the case head. Also measure the web expansion. Excessive headspace would not  cause these signs.

An overly large chamber headspace dimension would result in head-case seperations; specially with PMP brass. Treeman may remember this seeing he also owned an old Lee-Enfield. I also had a Lee Enfield No1MkIII* with very generous headspace. I could get 2-3 loads out of PMP brass before getting seperations. Not once did I get blown primers.

The only other reason I can think of is if the case were annealed right through. This would mimic an overpressure load.

@Ds J - please send me a WhatsApp - my phone was stolen and I have lost your number.

I would suggest the following :-
1. Use the existing charge but load with a COL that jams in the lands - QL calculates a pressure of 52K psi for doing that. That should be enough to fireform properly.
2. Anneal 3 cases so that the shoulder is also affected - do this after resizing.
3. You now have a softer font part that can stretch forward.
4. Measure the case lengths after shooting. If there is excessive head space those measurements should show it.

Photos to come.

The cases have not been loaded much - less than five times, and mostly with decent loads for practice.

And I am pretty sure that it occurred with another 168gr load and the same batch of  cases.

At one stage I thought it could be magnum primers (I mentioned it on this forum) but that was eliminated.

6 x masking tape is HUGE head space !, 1 x packing tape, the thin thin one, usually brown in color is usually used to measure this distance non professionally.
6 x masking tape is like worse than most bad .303 are.
I do not want to argue with janfred, but ?? I would blame head space for blown primers.

Next is I would have the barrel set back to rectify.

Blown primers can also result from cases with issues, I get it often when testing beyond max loads and then reload that case - the primer pockets stretch from ++ pressures. 

I would also test to see if this happens across the board with different reloaded cases from different batch's and loads.
 

Quote from: Treeman on May 01, 2024, 07:53 PM**************
The GunSite ban love affair is long standing.
 Fuck em !
When that false friend KK guy did his play up to me with that human horror Big T, the cause was good, get rid of a absolute cunt, the reasons only came out later when I stopped dancing to his commands. That whole GS is a little powerplay with the Superior Beings being the moderators. I must say however there are mods like Cammo that just moderate, no superior being perceptions.
             thought I would battle without GS, but I still have most of the guys on all other media.

The 2 you mention pretty much killed that site.  On the odd occasion that the site isn't down these days, it's just the same handful of people still posting.

The articles on the front page must be close to 10 years old now.

Well, blown primers are usually not a headspace problem unless it is mm's to large. If your firing pin can set off the primer, it shouldn't blow the primer.

Can you place a photo of one of the blown primers?

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