Headspace issue

OK, that wasn't readily apparent to me from the extraction pics. I should have reviewed all the pics in this thread before I continued after my bravo statement.

Chamber heaedspace gauges are always good, they will give you a clue as to the reason why there was a case separation in the first place. The most important measurement, that the shooting society really does not understand, is cartridge case head protrusion. That is the amount of case head hanging outside of the chamber. Too much and the sidewalls rupture. Excessive headspace, that is base to shoulder measurements, will develop if receiver seats peen or if the lugs set back which is a primary reason used weapons are headspaced. To see if there is structural failure going on in the locking mechanism. The shooting community only thinks of headspace in terms of sizing dies and shoulder set back.


I am going to state, that as long as the receiver seats are not peened, or the lugs set back, than the case head protrusion is as the gun was designed and built. It is my guess that the case head separation in your rifle was due to excessive chamber headspace. That the rifle was cut with a long and big reamer, which is fine for a military rifle. The military does not reload cases. Now, I have a Marlin lever action with a huge chamber. If I fired dry cases in the chamber, I would no doubt in one or two firings develop case head separations. This shows just how much the case shoulder has to move in the rifle.



what I did to protect my cases, was to fire new cases with a lubricant on the outside. These are some of the cases I fired in my Marlin.



What this lubricant does is prevent the case mouth and case neck from gripping the chamber during ignition. With dry cases and dry chambers the front of the case sticks, and the mid section has to stretch to meet the bolt face. If the chamber headspace is excessive, the case will break. However, with a lubricated case, the case slides to the bolt face, the case shoulders fold out to fill the chamber, and you end up with a perfectly fireformed, stress free case.

Then, you measure the things with a case gauge, and only bump the shoulders back 0.003" from the blown out position once you start sizing cases. You will need a cartridge case headspace gauge, or a comparator, to measure the base to shoulder before sizing, and after sizing. That ought to prevent case breakage due to excessive chamber headspace, and allow you to reload the cases many times.

This is an older, vintage action, so keep your chamber pressures less than or equal to 43,000 psia. These older Mausers were issued with ammunition which had this as their maximum pressures. As Boom Boom shows, exceed those pressures, and you can expect receiver seat set back.

Nicely done!

Ditto to Legionaire's comment, you obviously have knowledge of how to use tools.

Based on your pic, I'd say the chambering looks fine. Most likely had lug setback that created excessive headspace. Should be easy enough to fix your headspace when reinstalling the barrel by machining a little off the barrel shoulder so it can turn in slightly farther to make up for the lugs. A full turn in and adjust the bolt so the iron sights aren't clocked or go century monkey with canted sights.

Well, you do have factory ammunition for it. How about you set it up using that?

If you have a caliper and something with an appropriate sized hole in it to contact the shoulder you can measure an unfired round like this.



Then remeasure the case after you fire it to see if you are too loose. If you don’t plan on reloading it might not matter anyway.



That said, the separated case you had to remove is an indicator that the head space was not correct, at least with the ammunition used.

http://pacifictoolandgauge.com/saam...r-7mm-mauser-7x57-saami-headspace-gauges.html

Foster field gauge
https://www.amazon.com/Headspace-Ga...ds=headspace+gauge+7x57&qid=1585883331&sr=8-7

I think you'll be fine with a field gauge and then sticking to SAAMI spec ammo if it's a very tight fit or won't close, but there are some other folks posting on this thread who probably have better developed views on the issue if, perhaps, an overabundance of caution, and hearing from them on the matter will help make a more well rounded decision.

@DocRock is correct that you can use a field gage as military rifles usually run long and Forster's gages are fine. So are PTG's. This will never be a match rifle so minor variances in the chamber by headspace gage are not generally an issue. If you do not reload, then firing new brass is usually no problem. If you do reload, you have to pay scrupulous attention to the brass condition and usually neck size only for that particular rifle. The case web starts thinning excessively in a large chamber if you full length resize and then trim.



Alternatively, you can do as @Slamfire recommends up above but I suggest you do a search and read his posts on that particular method--it does increase bolt thrust a bit but Slamfire has provided quite a bit of evidence that it doesn't do so excessively.

However, unlike IllinoisBurt, if your receiver lug locking surfaces are setback, then one of two things has happened. One is the case hardened surface of the receiver lug recess is worn through exposing the softer core that Mausers share in common. This is simply from the wear caused by the bolt lugs and receiver lug locking surfaces grinding each other or by some attempt at using valve or lapping compound to get the bolt lugs to a higher engagement percentage. This lapping method is often using in accurizing Mausers but it is critical to cut the hardened layer on the receiver lug locking surfaces to an absolute minimum. The case hardening on old Mausers can be very thin.

This can be fixed if you reheat treat the receiver which can only be done correctly at a few facilities. The difficulty arises is that Spanish Mauser, in particular, can vary a bit on their exact metallurgy which is why you need expert facilities doing this. Otherwise, the receiver can warp and that is that.

Another is to set back the barrel and do as IllinoisBurt suggests, however, if the locking surfaces of the receiver are worn through, expect that the rifle will go out of headspace relatively quickly which means that you have to more or less use a headspace gage to check frequently to determine if the locking surfaces of the receiver are set back again.

That method is really only useful if you plan on firing a couple of rounds to celebrate your grandfather and then put in the safe. Kind of expensive fix but people have different reasons for doing stuff. Another alternative is stick to low powered cast boolit loads to stretch out the life of the rifle.

The second type of lug setback is where an overpressure event occurred and the metal from the locking surface is deformed with ridges, valleys, etc. I suppose that someone could grind those off and then reheat treat the receiver or do something complicated like tig welding etc. and reheat treating but then you are at status one again.

This happens because Mausers, as a safety mechanism, are composed of a case hardened carbon steel skin and a softer inside. A Mauser that is case hardened through is brittle just as the 1903 brittle receivers are and these can shatter in an unpredictably fashion. So, a normal Mauser faced with a cartridge say of 65,000 psi is designed just like today's cars are--to deform the core while the skin keeps the material together instead of shattering. The only problem is if a person keeps firing 65,000 psi cartridges, the receiver lug shoulders keep deforming backwards in response to the bolt lugs being thrust back. Ideally, the bolt gets harder and harder to operate and extraction becomes difficult. These are warning signs that something is amiss. But, if Bubba keeps on with his experiment and the brass is stretched enough to separate, then hot gas from the cartridge is introduced into the receiver body with unpredictable results that just might result in a catastrophic failure of the rifle and/or medical consequences to the shooter.



My recommendation is if you find the receiver locking surfaces setback, then simply get another 93 Spanish receiver. Sarco is selling them for $20 and you can find quite a few on gunbroker, etc. for slightly higher prices.

Dealing with rifles that have excessive headspace (within reason) is easy if you reload for that condition -- it is no different than some "improved" cartridges with the shoulder moved forward. This is also a technique used when creating brass from another, more common chambering.

The simple solution is to slightly neck the round up and then neck it back down to the original diameter, but leaving a false shoulder slightly ahead of the original to create a crush fit when chambering the round. Now you've created a condition where the round won't stretch linearly, and will fill out the new shoulder as it is fire-formed.

After the new brass is created, it is dedicated to that rifle and loaded appropriately for the chamber. Meaning you don't set the shoulder back any more than necessary for easy chambering. With a two lug bolt there is enough camming power to force a round that hasn't had the shoulder touched by the reloading die, a lever might require a bit of shoulder set back to chamber easily. No special gauges are required, the rifle itself is the gauge in this case.

Rounds fired once in a chamber with headspace on the high end, but reformed appropriately are no problem. The Lee-Enfield is a prime example due war time tolerances, wear and the flexible nature of the action. If you set the die to smash hard to the shell holder and smash that shoulder back as far as you can, the brass might last up to three or four firings before it displays signs of a head separation or actually does split laterally. Reformed without mashing the shoulder back and I've had cases I've use up to ten times before I tossed them.

Greasing a case only serves to greatly increase bolt thrust and WILL compound your headspace issues over time. This was formerly one technique for proof testing guns along with higher pressure cartridges.

Good luck all.

Where on earth did you find that firing pin?! Outstanding job. I’m about to go through the same thing only twice! My dad built a .257 Roberts on a Spanish Mauser action and it was what us kids used to kill or deer. The tip broke off of the firing pin recently. We have a bunch of small ring Mauser parts that dad collected but no firing pins! We have the parts to build a new one for all the little ones my brothers and I have, but no firing pins