32-40 win primer movement

[Coyotefurharvester]

Loading and shooting a rolling block in 32-40. Unfired brass, starting powder charge, 160 gr cast bullets. Both pistol and rifle primers are protruding several thousandth after firing. My experience says low pressure, but have no previous experience with cartridges that the rim controls the breech face clearance. Doesn't appear to be any gas escaping around the primer, just the primer movement. Primers seated 4-5 thousandth below flush.

 

[Rook 6]

Not really enough info to go by here. Under pressure is one possibility....

 

[dellet]

The amount the primer is sticking out is basically your headspace, it's worth measuring as a piece of reference data. Other than that pretty normal.

More of a mid pressure load. Enough pressure to expand the case and stick it to the chamber wall, not enough to push the case back to the breech block.

Not a bad place to be in a weaker action like that, unless the firing pin catches on the primer. If the case is not being driven back into the block it minimizes thrust into the action.

 

[Uncle Ed]

My 30-30 primers always protrude, and is normal al lower chamber pressures. This is because even at the max pressure of 42,000 psi for the 30-30 the pressure is not great enough to push the base of the case to the rear making the brass stretch.

In fact any time you make a workup load starting at the suggested start load the primers will protrude.

Below the primers will protrude until chamber pressures is great enough to make the brass stretch back and contact the bolt face.

This makes me ask, doesn't anyone make work up loads starting at the suggested start load anymore. And watch the primer become flush as the pressure increases with higher pressure loads.

 

[JohnKielly]

PO Ackley demonstrated primers setting back with loads below that necessary for the brass to stretch in an experiment recorded in one of the two volumes of "Handbook for Shooters & Reloaders"

 

[Uncle Ed]

The "air space" between the rear of the case and the bolt face is called head clearance.

Then if you add the rim thickness to your head clearance that is the rifle's headspace.

 

[Uncle Ed]

PO Ackley demonstrated primers setting back with loads below that necessary for the brass to stretch in an experiment recorded in one of the two volumes of "Handbook for Shooters & Reloaders"

PO Ackley removed the locking bolt from a Winchester 94 30-30 Improved and remotely fired the rifle.

And nothing happened, the case gripped the chamber walls and all that happened was the primer backed out.

Below on the left a fired .303 British reduced load and the rifle is past max military headspace of .074. At low pressure, all that happened was the primer backed out.

Below our British friend Laurie Holland posted the photo below here of factory loaded 7mm Mauser ammo. The ammunition was fired in an old surplus military Mauser rifle that might have been over max headspace.

My point being even the factory ammunition did not generate enough pressure to make the case stretch and contact the bolt face.

 

[dellet]

PO Ackley demonstrated primers setting back with loads below that necessary for the brass to stretch in an experiment recorded in one of the two volumes of "Handbook for Shooters & Reloaders"

That's how you end up with carbon and soot down the case or even a collapsed case, and a flattened primer. Showing both high and low pressure signs.

Remington 1 1/2 pistol primers are a good way to have that happen.

Also very common with sub-sonic loads where slow for application powders are used. Bore pressure drops enough to loosen the case grip to the chamber, but still enough to push the case back against the bolt or breech face and seat the primer.

Finally, a squib load can have a fully seated primer for the same reason. I have never seen it in a bolt action, but when you open the action of a rolling or falling block and have the case pop out do to trapped pressure, it's a bit of a surprise.

All that to say, for every "rule" there are exceptions. Ackley was a very much a scientist through experience, not speculation.

 

[JohnKielly]

That's how you end up with carbon and soot down the case or even a collapsed case, and a flattened primer. Showing both high and low pressure signs.

No.

A low pressure case in a generous chamber will grip the chamber walls sufficiently without expanding backwards.

How else would revolvers work?

 

[dellet]

No.

A low pressure case in a generous chamber will grip the chamber walls sufficiently without expanding backwards.

How else would revolvers work?

Revolvers are a good example of what i’m talking about. A low pressure load has enough pressure to expand the case against the cylinder, but not enough to push the brass back against the frame. Certainly not enough to stretch the brass. There is a big difference in case stretch, and case movement

If the case does not move back and reseat the primer in a revolver, the hanging primers can and do lock up the cylinder. Classic low pressure revolver jam.

If you take that idea to an extreme, use a non magnum or low pressure rated primer like a Remington 1 1/2, you can have enough pressure to flatten a primer but not enough to get a proper seal between the case wall and chamber. High pressure signs on the back end, low pressure signs on the front. The primer is reseated, because the case slipped.

I can pretty easily create carbon tracks down a case wall, and a flattened primer on command. If I cheat and use a low pressure pistol primer, I can get a dent below the neck line or a crease in the neck and mouth of the case.