How important is it to check the headspace in a Milsurplus rifle?

[CHAUKA]

I just purchased two Russian Mosin rifles both come from the Izhevsk Arsenal a 1942- M91/30 & 1944r - M44.

How important is it for me to have the headspace checked before I take to the range?

Century International Arms was the importer, their tag was on the rifles.

[PA Rifleman]

Originally Posted by CHAUKA

I just purchased two Russian Mosin rifles both come from the Izhevsk Arsenal a 1942- M91/30 & 1944r - M44.

How important is it for me to have the headspace checked before I take to the range?

Century International Arms was the importer, their tag was on the rifles.

There's been a lot of discussion about the importance of head clearance (AKA "headspace") on the Mosin rifle, so I won't re-write what's already out there. If the witness numbers all match, it's probably serviceable.

I *always* check mine, I've detected two with excess headspace out of probably several hundred I've checked over the last twenty years or so. If you don't have a gauge, or know someone with one they're available from Brownells, Midway or direct from the manufacturer (Clymer, Forster, etc). Better gauges are the pilot-type, cheaper gauges will be button type. Either will suffice.

Also be advised that the 7.62x54R is a rimmed cartridge, so rim thickness will affect headspace slightly.

I haven't heard any reports of incipient or real case failure from headspace on a Mosin rifle. I would check the firing pin & cocking piece threads to make certain they are not stripped, as I had a close call with one that could have fired out of battery from this had I not found it during a routine delivery check.

http://tinyurl.com/ywnm4a

Tons of information.

Definitions, explanations - link

Fulton's explanation - link

Brownells Bench Talk on headspace gauges - link

[Steve in PA]

The idea or reason for checking is because the bolts usually aren't original to the rifle, therefore the headspace might be off.

[PA Rifleman]

Originally Posted by Steve in PA

The idea or reason for checking is because the bolts usually aren't original to the rifle, therefore the headspace might be off.

One Mosin I flagged for excess headspace had all matching witness numbers and appeared to be a recent arsenal rebuild. Whether it was truly all original or had replacement (blank) parts stamped to match isn't known, but from our perspective it doesn't matter.

The Russians made unnumbered parts for replacements, as I've seen a number of blank (unnumbered) bolts.

What's more, the Mosin bolt head supports the cartridge during firing, and is a separate piece from the bolt body. A matching bolt body doesn't mean the bolt head's original on a Mosin. (diagram link)

Bolt body is #2, and bolt head is #6, below.




Sidebar: check thread integrity between parts #1 and #3. If loose, damaged or stripped, replace both. A problem here could cause the trigger to lose control of the firing pin, resulting in an uncontrolled discharge without warning.

[CHAUKA]

PA Rifleman & Steve thanks for responding back.


I will check out the links - you were kind enough to provide.

That is a great photo break down of the bolt!

A problem here could cause the trigger to lose control of the firing pin, resulting in an uncontrolled discharge without warning.

That sounds very...very Bad! would engauging the safety stop that?

[PA Rifleman]

Originally Posted by CHAUKA

That sounds very...very Bad! would engauging [sic] the safety stop that?

Attempting to use the safety may hasten a discharge if the threads were marginal.

The firing pin is under spring pressure forward, and the cocking piece holds it back. The firing pin screws into the cocking piece and the trigger fires by releasing the cocking piece. If the cocking piece separates from the firing pin, the firing pin will fly forward without warning. Thus, the trigger cannot control the firing pin.

To engage the safety the cocking piece must be pulled back further than the trigger normally holds it. This would momentarily increase the spring pressure on the firing pin beyond the pressure it’s under when ready to fire.

To keep this in perspective, I’ve only seen this once out of hundreds of Mosins, but that’s all it took for me.

I suggest replacing both if you suspect this condition, and condemning the old parts. Better yet, destroy the old parts.

Originally Posted by Steve in PA

The idea or reason for checking is because the bolts usually aren't original to the rifle, therefore the headspace might be off.

Steve: afterthought -- this would be valid statement with a Mauser-type rifle that uses a one piece bolt.