milsurp headspace

[majormarine]

someone told me that matching bolt and receiver is required to ensure that the headspace in a milsurp rifle (ie. WWII) is okay, especially while shooting these old rifles.

others told me that milsurp rifles were built in such a way so that they are interchangable in parts; therefore, headspace is not a concern with mis-matched parts.

so, which one is true?

 

[Randy Carriere]

I don't think that matching is exactly necessary as some matching ones can be pretty excessive as far as headspace go's. Matching does give a hint that it probably has'nt been altered since last leaving the factory where it was manufactured/refurbished, and a better chance that its acceptable. Only way to be sure is clean chamber/locking lugs very well and test with some headspace gauges. I have a turkish mauser bolt that fits quite well in a k98 stripped action. In its original action though, only 1 lug bears against the receiver surface. In basic training we had to carry that FNC1 everywhere we went but only got the actual breech block at the firing range. As I recall, we all just fished them out of a an old metal ammo box and then put in our rifles and started shooting. We never had problems of casings separating or anything like. This of course is a military standard where you not looking for glint edge accuracy or any reloading/case life considerations. Just that any rifles there could be feed any ammo there, from any magazine there...and function properly. Only way to know for sure is to test with headspace gauges.

 

[Hitzy]

someone told me that matching bolt and receiver is required to ensure that the headspace in a milsurp rifle (ie. WWII) is okay, especially while shooting these old rifles.

others told me that milsurp rifles were built in such a way so that they are interchangable in parts; therefore, headspace is not a concern with mis-matched parts.

so, which one is true?

Matching numbers is desireable but in no way garantees headspace will fall within commercial guidelines. Then you have Mosin's and Lee's that have un-numbered bolt heads so you have no idea if it's even the original one.
That said, headspace is a really overrated concern for milsurps, I only have one that passes a commercial no-go guage (US M1917 in 30'06). The military was more concerned with reliability, hence generous headspace, and you will find that 75% or more of milisurps will swallow a commercial no-go guage, you really need to test it with a military field guage. These can be 10 to 20 thou (or more) larger than a commercial no-go guage. If it doesn't pass the field guage then it should be worked on. Any new factory loaded ammo will handle a one time stretch of 20-30 thou, and if you reload and it's a bolt gun, just neck size and you won't have any problems. I wouldn't full length size a case that stretched that much though as you risk the chance of head speration.

 

[Andy]

What Hitzy said X2

We haven't had a headspace thread for a while. :wink: Usually at the beginning we hear something like "Excessive headspace is dangerous and can cause your gun to explode, causing harm to the shooter - have it checked out by a competent gunsmith". This is nonsense of course. Every year, several boneheads load 308 ammo into their 30/06 and fire away (the 308 fails the 30/06 Field gauge by about 0.380"!). Sometimes it goes "bang", and all you get is a fireformed 308 case that looks like a long 45 ACP, not pieces of gun and shooter distributed over a 10' radius. Should the same bonehead then force the same case back into 308 shape and repeat a few more times, you would see some form of casehead separation which is unpleasant at best. Should you unwisely not wear eye protection and your gun has less than excellent gas-handling features, you are looking (no pun intended) at possible eye and/or face damage.

Yes headspace matters, and yes you should check it. If it is too "short", ammo won't chamber, if too "long", you are pretty much forced to either fire the case only once, or neck-size only. But do I have bolt guns slightly out of spec (i.e. 0.020-030" or so over Field that Hitzy suggested) shelved, or have the barrels set back and rechambered by a gunsmith? - no. Let's face it, most milsurp shooters on this board don't reload, they just shoot their milsurp ammo once and relegate it to the scrap bin. Even more reason to live with excessive headspace.

Headspace can be checked at home with nothing more than an unfired case, a case fired in your gun, and a micrometer. Measure the magnitude of the growth in shoulder position, record it somewhere and forget it. Then set aside brass for that particular gun and neck size only. When it will not longer chamber after neck sizing, F/L size it to the extent that it will just chamber and continue to use it.

There are those who will say that what Hitzy and I have said is irresponsible, that we need to err on the side of extreme caution, work with the lowest common denominator, etc. I think it best that things be understood and people left to make their own decisions with the information provided.

 

[Claven2]

What Hitzy said X2
"Excessive headspace is dangerous and can cause your gun to explode, causing harm to the shooter - have it checked out by a competent gunsmith".

Not totally nonsense. I would still have it checked out. Some headspace IS dangerously excessive and can cause separation on first firing, but it is, admittedly, uncommon and more likely to injure you than to cause explosion.

Most headspace problems can be compensated for by proper reloading techniques though

 

[10x]

Headspace can be checked at home with nothing more than an unfired case, a case fired in your gun, and a micrometer. Measure the magnitude of the growth in shoulder position, record it somewhere and forget it. Then set aside brass for that particular gun and neck size only. When it will not longer chamber after neck sizing, F/L size it to the extent that it will just chamber and continue to use it.

Another way to check for excessive head space is to take an unfired, unprimed case and drop it in the chamber. Place a fired primer over the primer pocket and close the bolt very gently. Open the bolt and see how far in the bolt has seated the primmer.
It is a bit more dificult on M98 type extractors as the extractor has to be removed to do it this way.
Having the primer stand flush or just a little bit proud of the case head indicates that headspace probably isn't a problem. Having over 10% of the primmer stick out shows that there is a bit more tolerance with that particular case or there may be excessive headspace.
Remember to do this with a clean chamber as well. I watched one gunsmith check headspace, confirm it was "tight" and there was a wood shaving stuck in the chamber frome when he had relieved the stock to make room for a the low bolt handle he had installed.

 

[Andy]

That's a good way. Another that allows the extractor to stay in place, is to apply consecutive layers of aluminum tape to the cartridge face until the bolt handle closes with difficulty. Remove the tape and measure the thickness. Gives a rough approximation, at least letting you know you're in the ballpark.

I forgot to mention that the common practice of fireforming wildcat rounds from their parent case frequently involves headspacing a full-strength factory round between the boltface and the bullet-rifling juncture, often with the shoulder "hanging in mid air in the chamber". Upon firing, the shoulder is blown forward and out, sometimes quite a distance - and with complete safety.

So we seem to all be in violent agreement, although the thread has moved away a bit from the original intent of the posting.

 

[Test Pattern]

someone told me that matching bolt and receiver is required to ensure that the headspace in a milsurp rifle (ie. WWII) is okay, especially while shooting these old rifles.

others told me that milsurp rifles were built in such a way so that they are interchangable in parts; therefore, headspace is not a concern with mis-matched parts.

so, which one is true?

neither one is true. Whoever told you these things shouldn't be shooting milsurps.

Headspace gauges are required to determine proper headspace. Matching numbers (or lack thereof) are inconsequential to this exercise

 

[Beann]

I figure I'll wade in a bit on this - matching serial numbers are not a must, but do indicate that the weapon has probably not been messed with too much. It's is desireable but not a requirement.
Next, headspace is important. If it is excessive, then it will cause the casing to stretch and if too excessive, then the case can be dangerously weakened and possibly rupture-- usually extremely rare, but still a possiblility. Insufficient headspace can cause problems closing the bolt/breech and consequently problems opening the action after firing-- again fairly rare.
My advice, being a military Wpns Tech for 22 years (and counting), is to get the headspace checked using the proper gauge(s) if you are in doubt. There are ways to check it, if the proper gauges are unavailable but a knowledgeable gunsmith is the best to do it and to interpret the results. Also, a good look at the locking surfaces of the bolt/breech-block and their bearing surfaces in the receiver can give you a good idea of how well everything fits together.

Good luck.

 

[TimC]

Putting different working parts into your rifle when I was in got you a weekend where the sunshine grows in stripes. serial numbers were everything with the SLR when I served and random checks at the armoury and when issued got you into trouble if the numbers didnt match. headspace is more important admittedly on a bolt action rifle which is why armourers were issued go/no go guages and shims and spare boltheads not serial numbered to allow safe shooting to continue!

 

[Hitzy]

As long as the casehead is held fairly close against the boltface, which is what the extractor does in any CRF milsurp (90% of your bolt milsurps are CRF) , you won't get case head speration even if the headspace is massive.