8mm Mauser, Mauser expert advice please

[snert]

yesterday I was volunteered to shoot an old commercial (pre-war) Mauser in 8mm, for a friend who no longer has the eyesight for the open sights (like I do ). Nice old rifle, shooting a mild load with 160 ish bullets. It shot fine, ejected fine, no strange brass stretch, rings, etc. However all three cases showed evidence that the primer was backing out at firing. Any mauser guys have a guess why? I saw no issues with bolt face upon exam. As a precaution the loader backed load down even more.

 

[Ggmac]

Too many variables but I guess the headspace is off . Was it a 98 or other , all matching #s or mixed . What ammo ,commercial modern , old military , brass or steel case ?
Can you send a pic of rifle and or brass?

 

[fguffey]

Nice old rifle, shooting a mild load with 160 ish bullets. It shot fine, ejected fine, no strange brass stretch, rings, etc. However all three cases showed evidence that the primer was backing out at firing

Commercial Mauser: and then:

As a precaution the loader backed load down even more.

The backed out primer indicated the load was too light in the beginning. The backed out primer indicated the case was too short between the shoulder of the case and case head. There are those that claim the case head space etc. etc., that would work if the case had head space. It would help if someone measured the distance the primer was protruding.

If it was my rifle I would form cases that would fit the chamber from the shoulder of the chamber to the bolt face; meaning I would cut down on all that case travel. Reducing case clearance does not guarantee the primer will not protrude when reduced loads are fired.

F. Guffey

 

[Laurie]

Just as F. Guffey says. If a full-pressure load, the cases will show stretching / incipient case separation with completely flat primers; if a low pressure load, the case (luckily) doesn't stretch and the primer remains backed out from the case-head on extraction. Here are two lots of factory 7X57 fired in a rifle with excess headspace - RWS that was full pressure and stretched / flattened primers; US PMC low-pressure with backed out still radiussed primers

 

[snert]

OK Laurie, that confirms what I was seeing. Perfect exact replica of the brass I had in my hand.

The firearm is a matching numbers commercial Mauser with a "butter-knife" bolt, full length sporter stock, express sights and some engraving. Beyond that, I have no Mauser knowledge whatsoever.

I agree with Guff...I would venture that the headspace is long and the loads were "full length sized" on RCBS or Redding dies. They are reloads.

I will spend a bit of time with him and encourage him to adjust things to allow less setback. And I will check his data a bit. Sadly, he is aging and I think that sometimes he misses things.

I will try to get a photo (if he will allow it) and the brass...but by now I bet he reloaded it. It is all he does now.

Appreciate the help gents...

snert

 

[ebb]

You can ask Ggmac, around here we can him the Mauser man. But I would guess that is a very valuable rifle. I sure sounds COOL to me.

 

[DukeDuke]

did you load them in the magazine, or did you just drop them in the action without pushing down the follower?
in my 98 I have to push them down because of the claw extractor not engaging the brass properly, otherwise I get exactly what you got.

 

[snert]

did you load them in the magazine, or did you just drop them in the action without pushing down the follower?
in my 98 I have to push them down because of the claw extractor not engaging the brass properly, otherwise I get exactly what you got.

I shoved it into the mag...I think...

 

[snert]

I shoved it into the mag...I think...

I was a bit concerned, given the unk history of the gun, my small doubts about the reloads, and frankly, my aging eyes. I was stunned to have a 2 1/2 inch 3 shot group at 50 yards. It shoots better than i could see. Double set trigger helped...smooth as butter.

 

[Laurie]

One thing you have to watch with pre-war German sporters is bore dimensions. When the German military switched from the original 'I' (usually erroneously called 'J' because of Gothic script) Patrone with its 0.318" diameter bullets to the 'IS' (or 'JS') uprated model in 1904 with its 0.323" bullets, many civilian German gunmakers didn't follow suit for some reason.

So, sporting rifles built on M1894/5 actions and even many built on later '98 actions, of both military and commercial origin often employed 'tight' barrels up until the outbreak of WW2. They generate much higher pressures than proper 'S' barrels when loading normal diameter 8mm bullets.

That's one reason why the SAAMI MAP for 8X57mm is low, and many American ammunition companies load it to even lower pressures. The other reason was large numbers of ex German military M1888 'Commission' rifles imported into the USA as cheap surplus items last century which unless subsequently rebarrelled for the 'IS' cartridge all had the earlier chamber and 'tight' bores. With a relatively weak 1880s era Mannlicher designed action, modern full European CIP pressure 'IS' cartridges can produce dangerous pressures.

 

[fguffey]

Commercial Mauser:

The 98 Mauser is a control feed design, as pointed out it is a bad habit to push a round into the chamber without feeding the case up from the bottom. There are advantages to control feed and the 'big' claw extractor. I have fired 8mm57 ammo in an 8mm/06 chamber. The difference in length between the chamber and case from the shoulder of the chamber to the bolt face was .127"; meaning there was .127" clearance between the shoulder of the case and shoulder of the chamber. When fired the case did not stretch between the case head and case body and the shoulder of the case did not move.

Back to custom; the builder of the rifle could have changed the design enough to allow for push feed meaning he could have built the rifle so the extractor would jump the rim for push feed.

F. Guffey