Simple headspace question

[browneu]

This may be an ignorant question but I just don't know and I've just started getting into milsurp. Should you always check the headspace of the rifles you buy? I clean them and check the bore and barrel for anything out of the ordinary but didn't know about the headspace. I only have two Mosin's thus far.

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[Vaarok]

With some rifles it matters more than others. A rimless case, it's more likely to cause issues, since the cartridge headspaces on the shoulder, and if the chamber's too long the case will have to stretch to fill, and could tear around the base and spill pressurized propellant gas back at you- a casehead separation.

A rimmed case headspaces on the rim, which provides an extra seal and means headspace matters much less. However, the Enfield has rear-locking bolt lugs and receivers known to stretch over time, meaning the bolt won't necessarily hold the rim flush with the chamber mouth and give a good seal.

With Mosins, where the bolt is front-locking and the casehead is rimmed AND enclosed by the rim of the bolt face, it's almost irrelevant, and in other rifles like the Steyr 95, it doesn't matter much either.

Also, Arisakas and Mausers, it's a good idea to verify CHAMBERING, not just headspace. 8mm-06 and 7.7mm-06 redone rifles are floating around out there.

 

[303tom]

With some rifles it matters more than others. A rimless case, it's more likely to cause issues, since the cartridge headspaces on the shoulder, and if the chamber's too long the case will have to stretch to fill, and could tear around the base and spill pressurized propellant gas back at you- a casehead separation.

A rimmed case headspaces on the rim, which provides an extra seal and means headspace matters much less. However, the Enfield has rear-locking bolt lugs and receivers known to stretch over time, meaning the bolt won't necessarily hold the rim flush with the chamber mouth and give a good seal.

With Mosins, where the bolt is front-locking and the casehead is rimmed AND enclosed by the rim of the bolt face, it's almost irrelevant, and in other rifles like the Steyr 95, it doesn't matter much either.

Also, Arisakas and Mausers, it's a good idea to verify CHAMBERING, not just headspace. 8mm-06 and 7.7mm-06 redone rifles are floating around out there.

Good answer, could not have said it better !

 

[bigedp51]

Your not buying a new gun that has been proof pressure tested and inspected before leaving the factory. By law importers are not required to inspect milsurps, check headspace, etc. and its buyer beware.

A mosin that has been rearsenaled or overhauled is a safe bet for being in very good condition, and not needing headspace gages but remember you want matching numbers especially on the bolt on any rifle.

An Enfield rifle with a 18.5 Tons stamp on the barrel has gone through British Government inspection and was proof pressure tested before being sold out of service to the surplus market and is a good bet for not needing the headspace checked.

Buying milsurps from a vendor like Brian Dick at http://www.bdlltd.com/Home.html will ensure the rifle was inspected and gaged before you buy the rifle.

If you want the added piece of mind then at least a field headspace gage would be good to have. I collected mainly Enfield rifles and have three headspace gages, military minimum and maximum and a SAAMI NO-GO gage. By chance the SAAMI NO-GO of .067 was also the maximum headspace allowed after the new Enfield was proof tested.

"BUT" also remember this, military rifles have longer headspace standards than commercial U.S. made rifles for a given caliber. You could check the milsurp rifle with a commercial headspace gage and this could give the false impression the rifle failed headspace testing when the rifle still meets military headspace standards. Bottom line, if you do buy headspace gages make sure you get the right ones.

Below, on a British Enfield rifle the headspace can be decreased by changing to a higher number bolt head.

 

[bigedp51]

Vaarok

The .303 British Enfield rifle can have as much as .016 head clearance and still be within military headspace limits. This means the rim of the case is "NOT" going to seal anything. The Enfield rifle is very safe when case head separations occur as the gas is simply vented to the left and right of the shooter.

Below is a animated gif image showing what happens when a comertial .303 British cartridge is fired in the Enfield military chamber, the rim doesn't seal anything. Also please note the words "headspace" and "head clearance" and the effects on the case stretching in the web area of the case. The rim is driven forward by the firing pin and then chamber pressure pushes the case back against the bolt face. (The rim does not seal anything)



Below a reloaded .303 cartridge has been chambered in this Enfield that is going to have a case head separation when fired. Paper has been wrapped around the action to show where the gas has vented after firing.



The paper and the case head separation with very little damage to the sheet of paper.



The same thing happened to these .308 cases and NO one was injured, there is a difference between a case head separation and a massive case rupture from over pressure. If you want to see real pressure then pull my finger!