7mmx57 cases separating and neck splits

J

jiminthecorner

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Just got my "oberndorf " 98 back from the smith. If you recall I had to goto another bolt due to losing original. It wouldn't close unless I put extreme pressure on it. The bases were all "shiny " He refaced the bolt did a headspace repair and it fed the shells very smoothly. NOW!!!! the first shot blew the back of the shell completely off,(got it out /cleaning brush trick)/The I cautiously tried two more shots. Lots of "burnt" area around the necks AND long vertical splits!! OK says I its going back but I then tried some fresh loads in new brass and no problems! WTF!! THe first shells I had found somewhere in my shop and were obviously "old" stuff.

Now my question is: before I rush this back to the Smith,could it be old friable brass?Some of it was ww2 reloads.
I have some new WW brass and Lapua stuff too,and I'll reload these at Starting weights.. Any help on this appreciated. JITC
 
Case separation is commonly caused by excess headspace.
Test this by inserting primer partway in a case, close bolt on chambered case, remove and then measure difference between case length and case+outstanding primer length.

Split necks are usually caused by not annealing the necks often enough. They get work-hardened and brittle.
 
"...had to go to another bolt..." Fitted for headspace properly by your smithy, the new bolt should be fine? Headspace has nothing to do with feeding though.
"...W. W. 2 reloads..." Who loaded it? Never shoot other people's reloads.
 
Old brass becomes brittle over time. Try some new stuff, start about 3 grains low and work up, watch for signs of pressure every rifle if diffrerent.
 
With both head separation and case splits it really sounds like brass that has seen it's day. Especially, since new brass seems to present no problems. If the old brass dates from WW II , even if reloaded, depending on what country it was first made for it may also have been mercuric primed originally which does tend to deteriorate brass. If it was WWII surplus you were shooting do a very thorough cleaning of the bore, chamber and bolt (strip it down) with boiling water to remove any possible mercuric salt residue that might be present and cause corrosion/pitting of the metal. Relubricate as required following the water and drying.

Then measure your once fired new brass carefully with micrometer and vernier caliper to see if it is out of spec. in any radical manner. If you can see any apparent variation, beyond what might be considered normal expansion, from specs., go back to your gunsmith and explain the whole thing to him. He may want to recheck the head space. So far it appears the old brass had hardened and possibly corroded internally but only careful measurement will confirm that.
 
When a cartridge comes apart in the chamber STOP. Did you think firing more would cure it?

Not to be so harsh but I read this same idiocy every three days on here.

Only the gas handling design of many brilliant men saves the eye balls of the impatient.
 
Last edited:
david doyle said:
When a cartridge comes apart in the chamber STOP. Did you think firing more would cure it?

Not to be so harsh but I read this same idiocy every three days on here.

Only the gas handling design of many brilliant men saves the eye balls of the impatient.
Click to expand...

After the first shot I put on safety goggles and a glove on forearm. I had a blowup before years ago,still have the shrapnel.Thanks for the advice(every three days???!!,I should read this more often.) JITC
 
You can find the specs for your 7x57 at:
http://en.wikipedia.org/wiki/7x57_Mauser

I don't see the maximum headspace there, but from
American source it is 0.006". You can check this yourself as I described above.
I have fired WW2 ammo (not rifle) which did not split, so I must suspect a headspace problem.

Starting weights of powder charge should not be necessary, waste of time IMO. Note the spec. -> Maximum pressure 390 MPa (57,000 psi). If the rifle/cases can't take that you have a problem best solved by a *competent* gunsmith.
 
Old brass will split at the necks, It happened to me, I annealed the brass, problem went away.

The fact that factory rounds went off fine is a good indication, If the gunsmith did his work properly you shouldn't have any issues.

Go with new brass, I bet the problem will go away.
 
If you suspect it has anything to do with headspace, I doubt it though, check the headspace. Chances are that brass has been loaded and fired many times. It's repeated firing and resizing that causes brass to work harden. It's just as easy to pitch the old stuff.
 
JUst an UPDATE. Was at Bracebridge gun show today. Not too bad,Sold some stuff and had to pass Epps!!!!!!!!!!!!!! no way, went in and bought some "virgin " 7x57 brass. I dumped the bullet and powder from one of the "old "cases and put it in the new brass . Fired it and lo-and-behold no problems!!!!!! No splits ,no bulges ,no nothing ! Case looks perfect so must have been the old friable brass which has now been discarded, Still appreciate your sage advice guys!!!!!!! Thanks and we'll end this thread now!! JITC
 
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