8MM Mauser light loads primers backing out

[68lemans462]

Gun is a 98 mauser in 8MM original barrel, sporterized stock with a lyman peep sight.

Loads pictured are 45G and 47.5G H380 behind 170 grain speer hot cor, standard LR primer. Please disregard where it says 4350 in the picture, this is WRONG!

Shots taken from bench rest at 50 yards. Load looks to be working well, but the primers are backing out of the cases .005-.009".

Can this be caused by low pressure?

 

[gamestalker]

I've had primers back out a little before under certain circumstances, but what your describing here seems awfully indicative of excessive head space in the original 8mm M98 chambers.

Considering you reload, just make sure you don't bump the shoulders back more than what is necessary once they're fully fire formed, and you should be fine. But the spooky part is getting them formed when head space is really generous, and primers backing out .009" is pretty excessive, IMO. I would bet that if the primers backed out that far, that with factoring in brass spring back, that head space in that chamber may be as much as .010" - .012".

It might not be a bad idea to have a gun smith verify the head space go, no go.

GS

 

[jamesinalaska]

Primers backing out

Short Answer:
Light loads can push the primers out of their pockets.


Longer, more boring answer:

When a cartridge is fired, it is pushed back, rather hard, against the bolt face. (It is that whole Newtonian, Third Law of Physics thing.) But there are other dynamics happening as well, one of these is case expansion.

When a cartridge is fired the case begins to expand, uniformly, against the chamber. This expansion starts at the primer end and grows towards the seated bullet. (Imagine one of those long, circus animal balloons being inflated inside a 1" pipe.) This expansion performs a couple of services: it creates a seal in the chamber preventing burnt gasses from traveling backwards toward the bolt and the shooter, and it also, momentarily, locks the cartridge into the chamber. When a light load is fired, sometimes the cartridge will bounce off the bolt face, creating a gap of a few thousands of on inch before the expanding cartridge can "grip" into the rifle's chamber. In this instance, there would space created for the powder charge to push the primer out of its pocket.

Older military cartridges, especially soviet, were designed to prevent primers from blowing out of their pockets at critical times with the use of a crimp. Now, however, I think manufacturers use a type of dope, something like Locktite. But for sporting rifles, it best to stay above the listed minimums of in the load catalogs.

I do not load 8mm so cannot help you there.

 

[GooseGestapo]

Yes, too light.

I see it all the time with .30/30 in l/a rifle. Firing pin pushes and holds the round foward. Just enough pressure to expand the case, but not enough to stretch it back to face of bolt.
Higher pressure rounds will stretch the case and re-seat the primer.

Too, you might have a bit of head-space as other poster mentioned. Not uncommon for older mil-surp bolt actions.

edited to add; nice looking rifle. The jeweled bolt and stock look just like my .257Robt. built on a '39 LaCoruna action. My rifle, however, wears some nice checkering in "point pattern"...
I also have two Mark-X's imported by Interarms circa 1970's.

 

[Steve C]

Increase your load to at least 51.0 gr the start level listed in the Speer Manual 13 shown below, work up from there to no more than the maximum listed of 55.0 grs (compressed load). The primer backing out should disappear.

 

[68lemans462]

Correction, after reviewing reloading notes the load was NOT using IMR4350, it was with H380. Knowing this, are your opinions still the same? Thanks guys....

 

[MEHavey]

backing out of the cases .005-.009"

Totally normal for a light load that doesn't stretch the case back
to meet the bolt face -- and indicative of the headspace in play.

 

[GooseGestapo]

Speer #14 start load for H380 is 50.0gr and max. at 54.0.
Still, a LIGHT LOAD.

Don't full length size the brass either. Back off the sizer die two turns from touching the shell holder, then progressively turn the die in until the shoulder of the fired cases (from YOUR RIFLE) just touch the die.
This will reduce the backing-out of the primers and reduce the working of your brass. Will make them last much longer. I've got some .257Robt. brass that is over 30yrs old and still "working". Perhaps as many as 25 loadings.
Some have been annealed however...

 

[0to60]

Don't full length size the brass either. Back off the sizer die two turns from touching the shell holder, then progressively turn the die in until the shoulder of the fired cases (from YOUR RIFLE) just touch the die.
This will reduce the backing-out of the primers and reduce the working of your brass. Will make them last much longer. I've got some .257Robt. brass that is over 30yrs old and still "working". Perhaps as many as 25 loadings.
Some have been annealed however...

Why not simply use a collet die?

 

[Garrobo]

More like

a headspace problem to me.

 

[gamestalker]

If the load is indeed light, yes it will cause primers to back out pretty good. But there will also be some evidence of gases escaping down the side of the shoulder, and even the case body due to a poor seal. I was at the range a while back with my Son, and he had a bunch of 7mm RM reloads he bought at a yards sale that had been loaded real light with IMR-4350. After the first few rounds producing collapsed shoulders, and primers backed a 1/3 of the way out of the pocket, he decided to have me pull them and fix the problem.

There is also the possibility that the shoulders have been bumped back too far, thus creating excessive head space. If dealing with a good modern action and barrel known to be in spec, I will initially seat my bullet long enough to jam into the lands slightly. This keeps the case head against the bolt face, and then load a mid range charge of a slow burner to help get those that brass properly fire formed to the chamber.

GS

 

[fguffey]

But there will also be some evidence of gases escaping down the side of the shoulder,

If the case does not seal the chamber and gas flows between the chamber and case the primer will not protrude. If the case locks onto the chamber but does not have enough pressure to seat the case head against the bolt face the primer will protrude.

Then there are those that lube their cases, lubing the case prevents the case from locking to the chamber. When the case is allowed to slide the case can not lock to the chamber. The sliding case seats the primer.

Then there are artifacts, read the case to determine what happened when the trigger was pulled.

F. Guffey

 

[MEHavey]

If the case does not seal the chamber and gas flows between
the chamber and case the primer will not protrude.

But it will...
Backout occurs immediately as the exploding primer tries to funnel itself through the (relatively) tiny flash hole.
Try just shooting primers in a revolver sometime. Every primer will back out of the case to meet the shield face.

 

[fguffey]

Try just shooting primers in a revolver sometime. Every primer will back out of the case to meet the shield face.

I could do that, there would be absolutely no logical reason for doing it and I will promise you would not understand the sequence of events.

F. Guffey

 

[MEHavey]

I will promise you would not understand ...

To be sure....