Well, that's a first for me (blown primer on factory ammo)

[NorthIdahoDude]

So, I finally got my mauser back from the smith with a shiny new 7x57 Benchmark cut-rifled barrel. I'd picked up 100 rounds of Norma 7x57, for hardly more than I'd pay for 100 pieces of Norma brass, and have been breaking in the barrel + fire-forming all at the same time. On round 39, I got a face full of gas, which shocked the s**t out of me (no clue how many thousands of rounds I've shot over the years, but many, never once got that happen). Looking at it close, I'm thinking it looks more like a primer failure than an over-pressure event - primer is still round on one side, and still somewhat round right by where the gas obviously leaked. Case head not deformed that I can tell. Brass otherwise looks fine, bullet hit the same group as the previous 8 rounds. But still, definitely rattles my confidence. Anyone agree (or disagree) with my assessment of what happened here? (and yes, there's some pock-mark look to the fired primer next to it; this rifle has a generous hole for the pin to stick through).

 

[Sadie]

Deprime the case and see if it was possibly the cause.

 

[ResearchinStuff]

That looks more like a bad case than a bad primer. When the leak path is through the primer you get black gunk

 

[NorthIdahoDude]

I'll take a deeper dive with it today to see. It is quite a bit more black than my picture shows, and the primer does look deformed, but not uniformly, but it does almost look like there's a gap on the case side vs the primer side that vented the gas.

 

[Moose83]

Is this the Norma whitetail factory loads?

 

[NorthIdahoDude]

Is this the Norma whitetail factory loads?

Yes

 

[NorthIdahoDude]

Definitely looks like a bad primer cup to me.

 

[NorthIdahoDude]

I can definitely see some etching where the hot gases were flowing, but otherwise the brass looks fine.

 

[ResearchinStuff]

Wow, I've seen primers vent but never one lose an entire side of the cup like that. Give norma a call

 

[Moose83]

Yes

I had a bad batch of this stuff in .243. It did seem to be loaded fairly hot. When I shot it early spring it did OK, but when I shot it fast in July I was blowing primers steady. I tore down the remaining boxes I had and checked powder charges out of curiosity. Charges ranged from 41ish grains to as high as 45gr iirc, so the QC seemed to be lacking. I emailed Norma about it but never got a response.

 

[NorthIdahoDude]

Wow, I've seen primers vent but never one lose an entire side of the cup like that. Give norma a call

Obviously I can't tell, but it doesn't really look like the side of the cut blew out, it looked like maybe it wasn't there in the first place?

 

[ResearchinStuff]

Yeah I agree, it might just have been missing to begin with. Which would also be very strange

 

[4th_point]

Glad you are OK and hope you provide a follow-up to whatever else you discover.

BTW, you got a face full of gas from a true 98 design with C-ring and notch for extractor? Or is it an H-ring or coned breach?

 

[NorthIdahoDude]

View attachment 1054642

Definitely looks like a bad primer cup to me.

And the far side looks so much thicker than the near side, which is the opposite of what you would expect from perspective given my camera angle. So the one side was really thick and this side was really thin, possibly missing a chunk. At least that's kind of what it looks like.

 

[NorthIdahoDude]

Glad you are OK and hope you provide a follow-up to whatever else you discover.

BTW, you got a face full of gas from a true 98 design with C-ring and notch for extractor? Or is it an H-ring or coned breach?

It's a Zastava manufactured interarms Mark X. Commercial Mauser. No clue which of those two it is.

 

[4th_point]

It's a Zastava manufactured interarms Mark X. Commercial Mauser. No clue which of those two it is.

I believe they are all H-ring.

You can check by removing the bolt and peering inside the action towards the chamber. A C-ring only has a slot for the extractor, on the starboard side, and looks like the letter C.

H-ring is sort of a misnomer but has the cut going all the way across, port and starboard. It was done for ease of manufacturing, but allows gas to enter the left raceway more easily which can end up in the shooter's face. True 98 should have a flange on the bolt shroud to divert the gas 90 degrees.

 

[PopNFresh]

crazy....
shot lots of the Norma whitetail in different calibers through at least a couple dozen rifles and never saw anything like that, it usually chrono'd faster than most other factory stuff I shot through them minus maybe superformance but it always grouped better. euros like to load them warm, maybe weak cup and max load

 

[NorthIdahoDude]

I believe they are all H-ring.

You can check by removing the bolt and peering inside the action towards the chamber. A C-ring only has a slot for the extractor, on the starboard side, and looks like the letter C.

H-ring is sort of a misnomer but has the cut going all the way across, port and starboard. It was done for ease of manufacturing, but allows gas to enter the left raceway more easily which can end up in the shooter's face. True 98 should have a flange on the bolt shroud to divert the gas 90 degrees.

It's had the shroud replaced with a Winchester style 3 position safety, which to be fair, is more trustworthy than that Rem-700 style nonsense 'safety' it shipped with from Zastava/Interarms. But def does not stop a bit of gas blow-back. I mean, I didn't get like a huge amount, wasn't wearing eye pro and I can still see, etc. But def got enough to wake me all the way up, LOL.

These Zastava's I think are more "mauser based" than "exactly a mauser". OEM trigger/safety was some Rem 700 looking cartridge affair. The safety has been removed from the trigger in favor of the shroud safety. Someday I'm planing to have a proper Mauser 2 stage put on it and tuned, but this one is pretty decent for a single-stage (clean 3lb even break). What you're describing as manufacturing short-cuts, I'd be shocked if they didn't take them for these, LOL.

I probably wouldn't even mess with this gun, except it's sentimental, and is enough of a mauser to be fairly cool, IMHO.

 

[NorthIdahoDude]

crazy....
shot lots of the Norma whitetail in different calibers through at least a couple dozen rifles and never saw anything like that, it usually chrono'd faster than most other factory stuff I shot through them minus maybe superformance but it always grouped better. euros like to load them warm, maybe weak cup and max load

Interesting. I've only ever chrono'd the Norma Whitetail in 7x57 and 6.5 Creedmoor, and it was pretty slow in both of those (2650-ish with a 140 in 6.5 CM, and a hair over 2600 with a 150 in 7x57. My handloads in 7x57 push a 150 up in the high 2700's with a 22 inch barrel, and 140's to around 2750 in a 24 inch 6.5, so I always assumed this stuff was pretty anemic.