stupid headspace questions

[bluebayou]

Okay, short of buying a NO GO gauge, what if I used the trusty calipers to measure a fired case?  The way that I understand this is that this Russian 91/30 might have a big enough chamber that it fires but that the cases shouldn't be reloaded. 

If I measured some fired BRASS cases, not steel ones as I am sure that they don't expand the same, then would I get an accurate picture of how big the chamber is?

I know that someone told me that I was overworking my cases in a Remington 700.  They recommended that I just go to a shoulder bump to size. 

Would a similar technique work if I have excess headspace?

[schnarrgj]

On the 7-62x54r, the cartridge is measured on the rim. I load for a few 91-30s and m44s. Needless to say, the chambers do very quite a bit on some. With these, I only neck size so that I do not work the casing too much. When you do that, you need have dedicated cases for each weapon. With large chambers, the brass is fire formed to the individual chamber when it is initially fired so that it fits that chamber just like when a case is fire formed for a wildcat. Full length resizng will shorten the life of the case. Be sure to inspect all your cases and watch the head. Hope this helps.

[iiranger]

Headspace in real, real simple terms is what supports the primer against the blow of the firing pin. In the rimmed Russian, it is the rim. Without expensive gauges you can check it by sticking pieces of "shim stock" --available at larger hardware stores or cut up a "feeler guage"-- to the base of a case with light grease/oil. Take the extractor off the bolt and close WITH GREAT CARE. Bolt leverage may be 15 to 1 and you can crush things if you are pushy... do damage, DON'T!. (Increase headspace...) Most of these guns are carefully checked by the importer for liability reasons. If you are doing hundreds of rifles, a headspace guage is not that expensive. But this means nothing and checks almost nothing about oversized chambers.

Real, real bottom line, you don't want the case coming back far enough to split and let hot gases which can be double the temperature of a cutting torch into the action... Pieces fly around and If you are lucky, you die. If not, white cane time???

There are many "techniques." Firing oiled cases so they don't adhere to the wall of the chamber... Not a great idea but it works to blow the shoulder forward. [AT YOUR OWN RISK...] Yes, not returning the shoulder to factory standard will help with safety and long case life...

The rest of your question... Militarys often have over sized chambers to take ammo that is dirty, corroded, etc. Since soldiers don't reload, they don't care. Reloaders, if they resize to minimum size work the brass ALOT and it fails that much sooner. Almost nothing to do with head space.

So many just "neck size" the neck of the case to hold the next bullet. This also gets you a bit more powder room. If you really want to "see" your chamber, you can cast it. Cerrosafe is a metal that melts in boiling water and standard to all machinists. You can use "garden sulphur" from the garden store. Melt it outside. It will not explode, but if it catches fire. STINK. Pour. Let cool. Push out GENTLY. Another machinist standard. You can mike the cast and see what might be over size... or out of round or ? You could use lead, less standard and more difficult... Or modeling clay, gently... But if you think you got quality and match accuracy from a Russian Arsenal (or Finn or ) probably not. Shoot it and enjoy... luck.

[1911crazy]

I started a while back buying "Field" headspace gages for all my surplus guns.  Then on certain ones I got the "NO-GO" gages too. (6,5mm swede,  7mm mauser,  308,  8mm mauser) Then on the calibers were i change barrels i got the "GO" gage for them.  I do have a no go for the 7,62x54r somewhere.  The guys on www.gunboards.com can tell you exactly how thick the disc has to be too.  I don't remember.  Most of the guys make there own mosin headspace gages.

[PigBoy Crabshaw]

Here you go:

http://hometown.aol.com/yankeng/myhomepage/business.html

-g

[Curtis]

I checked my Krag with a NO-GO gauge from Midway USA.  It was only $20 which I considered cheap insurance.  The stripped bolt closed on the gauge, but it was tight enough I decided it was safe to fire without checking with a field gauge.

Most of my "work up" hand loads had protruding primers which indicates that pressure was high enough for the case walls to grip the chamber, but not high enough to stretch the brass just forward of the case head.  I may try fire forming to move the shoulder up as was mentioned earlier but that entails some method of preventing the case from moving forward from the firing pin strike.  With the long throats on these chambers, I'm not sure I can seat even a large bullet out to the lands to accomplish this, but I don't know what else to try.  Maybe the oiled case trick mentioned earlier (at my own risk) using pistol powder and some light bullets like the 100 gr .30 cal speer plinkers.

If I can't get this brass to form to the chamber without stretching forward of the head, my brass life will be short and I will have to be ever vigilant for signs of incipient head separation.

Curtis

[Sweetwater]

For purposes of fireforming to push the shoulders forward, you can create a 'false shoulder' where you want the shoulder to be in the neck area with the expander plug from a larger caliber. It doesn't take make much to create a 'crush fit' that will help hold the cartridge in place while the pressure irons out the wrinkles. At least this is what I've read in various publications. It's a problem I've been fortunate enough to basically avoid. The closest I've come is to inadvertently push the shoulder back by improperly adjusting the sizing die, thus creating an improper headspace situation. Firing the rounds simply pushed the shoulders forward to their original positions and correctly adjusting the sizing die precluded recurrence of the problem. I didn't run into the condition where the cases moved forward when fired. I have been able, I think, to control the headspace in all my bottle neck chambers, even the ones that are supposed to headspace on the rim. I set the sizing die just low enough to kiss the neck and stay just above the shoulder, whereby the cases all headspace on their shoulders. I also keep my brass segregated for each weapon.

Regards,
Sweetwater

[Curtis]

Sweetwater, thanks for the false shoulder idea.  I think that will do the trick for my Krag and also forming brass in my Thompson Contender since all of my bottleneck cartridges headspace from the shoulder (even the rimmed ones).

Curtis