Ok...here's the deal. Original Jeffery rifle, new 333 Bertram brass full-length sized and trimed. Load of 60 gr of H4831....MILD...over a Fed 215 primer. Chronos at 2000 fps, and actual velocity of original cartridge is 2200 fps with the 300 gr bullet (Woodleigh soft). Cartridges feed and chamber fine. However....when fired and extracted, the primers are pushed out slightly...maybe a 32nd...and the cases...about 1/4" forward of the extractor groove have a "shinyer" look about 3/8" long...towards the neck. Case head expansion...nope, same as sized and unfired. The overall cartridge length and other dimentions match some original...well old anyway...Kynoch ammo. No hard bolt lift or other pressure signs. Has me perplexed.

HELP!!

Gary
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Well....maybe because the cases were .0055 too long???...would that account for the situation?
Think I loaded too hastily and didn't trim the new brass......old man momoment.

Gary
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Sounds like low pressure (backs out the primer) and perhaps a bit of roughness in the chamber to scuff the cases as they are being extracted. Love those .333s!

I must say that I haven't ever experienced backed out primers from a "low pressure" load. Interesting. The load was probably about 87-90% of max...would you consider that low enough pressure? There was no "over expansion" of the case head as I mic'ed all of the rounds....they were the same as new brass and unfired, but loaded, ammo.

Thanks.

Gary
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Backed-out primers are a fairly common occurrence when there's a bit of excess headspace with the ammo being used and it doesn't generate enough pressure to stretch the case on firing.

Here's how it happens on a rimless case:

First, either the head-to-shoulder length of the case is slightly less than the chamber dimension, or the firing pin blow is strong enough to actually force the case to shorten a bit against the shoulder of the chamber - this last occurs most frequently with cases that have very little shoulder like the .400 Whelen or with actions that have particularly heavy striker fall like the Mannlicher-Shoenauer.

Second, the firing pin blow pushes the case forward into the chamber.

Third, the pressure of the powder burning expands the case body to the point that it grips the sides of the chamber, leaving the base of the case still forward of the breech face.

Fourth, if the pressure is moderate it doesn't generate enough force to stretch the base of the case back to the breech face while the case body is held tightly to the chamber wall, but the primer is easily pushed out of the case back against the breech face.

Fifth, the pressure drops and you extract the case with the dangling primer.

In this situation of a bit of excess headspace, when the pressure is higher the same sequence of events takes place, including the primer backing out, but there's enough force to stretch the brass back to the breech face as well. In this case the primer will often appear to be very flattened. Brass that has gone through this cycle several times will separate near the head.

The same thing happens with rimmed rounds when either the rim recess is too deep or the rims are too thin.

Different brands of cases react differently to pressure. Thinner or weaker brass will stretch at much lower pressures than thick strong brass and the strength of the action doesn't affect the process.

Anyway, strange as it seems, backed out primers are a sign of low pressures.

Id say Head space also.

I have had primers back out when fireforming some 3006 brass in a 9.3x62, then the brown truck delivered my real 9.3x62 brass

Neck size, Load em again and shoot some more

Thank you gents.....an old dog just learned something. I had definitely had experience with incorrect headspace, but the primers didn't back out...and in one case I had case head seperation. I will neck size and let 'er fly.

Thanks again.

Gary
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NRA Lifer
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