HEADSPACE ON MOSIN?

[kcstott]

I can't specifically say on a Mosin as I've never had the opportunity to take apart the bolt.
But if it is based on a Mauser design or something close. It should have never been able to fire in a position that would allow the bolt to move rearward. Meaning that the striker is held in a safe position until the sear picks it up and holds it until the rifle is fully locked and ready. That is the way it should work. But a malfunctioning trigger, a malfunctioning operator (finger on the trigger) or a damaged or otherwise fouled up bolt shroud and cocking piece could cause an out of battery ignition.

Head space would not be a suspect in my mind with the fact given.

Question. How many rounds did the rifle fire before it failed? Not an exact number but were you able to shoot at least one round prior to the failure??

If so that would also point away from headspace and toward a mechanical issue.

[Kerplow]

I can't specifically say on a Mosin as I've never had the opportunity to take apart the bolt.
But if it is based on a Mauser design or something close. It should have never been able to fire in a position that would allow the bolt to move rearward. Meaning that the striker is held in a safe position until the sear picks it up and holds it until the rifle is fully locked and ready. That is the way it should work. But a malfunctioning trigger, a malfunctioning operator (finger on the trigger) or a damaged or otherwise fouled up bolt shroud and cocking piece could cause an out of battery ignition.

Head space would not be a suspect in my mind with the fact given.

Question. How many rounds did the rifle fire before it failed? Not an exact number but were you able to shoot at least one round prior to the failure??

If so that would also point away from headspace and toward a mechanical issue.

Forgive me for being daft, but how could a headspace issue cause an OBD at all?

[kcstott]

Oh, it also gave me an awesome scar in the center of my hand that makes me look like what I imagine Jesus' hands looked like after that whole cross incident.

You mean when he fliped over the money tables and pissed off the Jews that they in turned hired the Italians to bump him off??

[Fate]

jshoebot's accident sounds like firing pin protrusion issue (or an improperly seated primer) more than headspace problems.

As for the OP, Mosins almost never have headspace issues. If you reaaaallllyyy need to check it, only use the FIELD gauge and get a coin type so you don't need to remove the extractor. Battle rifles like the Mosin were built with loose tolerances so the "no go" test often fails. This is because go and no go are based on modern tolerances and have nothing to do with the safety of a milsurp rifle.

Honestly, if it chambers a round and fires without bulging the case, you're fine. And as far as peace of mind goes, the Mosin has one of the strongest actions of any milsurp ever built. You'll be fine.

[tujungatoes]

jshoebot's accident sounds like firing pin protrusion issue (or an improperly seated primer) more than headspace problems.

As for the OP, Mosins almost never have headspace issues. If you reaaaallllyyy need to check it, only use the FIELD gauge and get a coin type so you don't need to remove the extractor. Battle rifles like the Mosin were built with loose tolerances so the "no go" test often fails. This is because go and no go are based on modern tolerances and have nothing to do with the safety of a milsurp rifle.

Honestly, if it chambers a round and fires without bulging the case, you're fine. And as far as peace of mind goes, the Mosin has one of the strongest actions of any milsurp ever built. You'll be fine.

[kcstott]

Forgive me for being daft, but how could a headspace issue cause an OBD at all?

That's what I was getting at. Headspace was not the issue.

[Peter.Steele]

That incident sounds like a couple of problems all combined to give Jshoebot a really bad day.

1. Firing pin protrusion was too great
2. Weak / poorly adjusted sear
3. Badly set primer

I've got an M44 that has the weak sear. When you start closing the bolt it'll let the firing pin go. Normally this wouldn't cause an OBD - it'd just shoot when you got the bolt all the way closed - but with too much firing pin protrusion the gun can fire when there's still some air gap between the casing and the bolt face. If the primer isn't seated all the way in, then that isn't going to help matters either, because there could be even more gap between the bolt face and the casing.


Whatever the problem was, it wasn't headspace.

[Dan FS71]

If you want a ballpark without having to spend $$$ on gauges and have scotch tape and a caliper.

The differance between go, no-go, & field is about 3 thous per. Yes there is variation in rounds size. Stack layers of scotch tape on the back of the round until the bolt will ( just ) not close. Use a razor to scrape the layers off and measure with your calipers.

0-3 thous you headspace is like new
4-6 thou it's well used but still useable
7-9 thou you better buy a field gauge because you are close to a dangerious situation
10+ thous Don't shoot it. Yes they can blow up as in blow apart at high velocity. H20 jet cutters use about the same pressure and they cut threw all sorts of stuff very efficently, least of which body parts.

How would I go about checking the headspace on my recently purchaced Mosin 91/30? I dont want to fire it if is not safe to do so.

[nick]

jshoebot's accident sounds like firing pin protrusion issue (or an improperly seated primer) more than headspace problems.

As for the OP, Mosins almost never have headspace issues. If you reaaaallllyyy need to check it, only use the FIELD gauge and get a coin type so you don't need to remove the extractor. Battle rifles like the Mosin were built with loose tolerances so the "no go" test often fails. This is because go and no go are based on modern tolerances and have nothing to do with the safety of a milsurp rifle.

Honestly, if it chambers a round and fires without bulging the case, you're fine. And as far as peace of mind goes, the Mosin has one of the strongest actions of any milsurp ever built. You'll be fine.

This.

[Alex$]

Jshoebot, thanks for sharing, sorry it occurred. As all have stated, doesn't sound like headspace issue.

Kc, the mosin bolt is its own beast, but it will not allow the firing pin to protrude beyond the bolt face until the handle is started turning along the camming suface. On a properly gauged bolt it will not start to protrude from the bolt face until the bolt handle is 3/4 of the way to locking.

Now that I am thinking about jshoebot's case I wonder if a round did not properly chamber, the bolt was re-cycled causing another round to start feeding and the bullet hit the primer of the non-chambered round causing out of battery detonation... While fussing with a MN I observed this possible situation with dummy rounds.

I cannot claim to be a MN expert, but I have torn apart every one I have owned plus some of my friends as well. So I am somewhat familiar with them.

[kcstott]

If you want a ballpark without having to spend $$$ on gauges and have scotch tape and a caliper.

The differance between go, no-go, & field is about 3 thous per. Yes there is variation in rounds size. Stack layers of scotch tape on the back of the round until the bolt will ( just ) not close. Use a razor to scrape the layers off and measure with your calipers.

0-3 thous you headspace is like new
4-6 thou it's well used but still useable
7-9 thou you better buy a field gauge because you are close to a dangerious situation
10+ thous Don't shoot it. Yes they can blow up as in blow apart at high velocity. H20 jet cutters use about the same pressure and they cut threw all sorts of stuff very efficently, least of which body parts.

That approach will only work on rimmed, straight walled, or belted magnum cases. Do not use this approach to headspace a round the gages on the shoulder.

[kcstott]

Jshoebot, thanks for sharing, sorry it occurred. As all have stated, doesn't sound like headspace issue.

Kc, the mosin bolt is its own beast, but it will not allow the firing pin to protrude beyond the bolt face until the handle is started turning along the camming suface. On a properly gauged bolt it will not start to protrude from the bolt face until the bolt handle is 3/4 of the way to locking.

Now that I am thinking about jshoebot's case I wonder if a round did not properly chamber, the bolt was re-cycled causing another round to start feeding and the bullet hit the primer of the non-chambered round causing out of battery detonation... While fussing with a MN I observed this possible situation with dummy rounds.

I cannot claim to be a MN expert, but I have torn apart every one I have owned plus some of my friends as well. So I am somewhat familiar with them.

Thats a very good point and it is very possible.

[Dan FS71]

It does in fact work and work well. Headspace is the distance between the back of the case and the bolt face. The engagement of the chamber/round makes no differance as you are using the round that fits the gun therefore the engagement is correct.

It works just fine, try it and you'll find the truth of it.

That approach will only work on rimmed, straight walled, or belted magnum cases. .

[DennisCA]

How would I go about checking the headspace on my recently purchaced Mosin 91/30? I dont want to fire it if is not safe to do so.

Google the following phrase:
"how to check the headspace on a mosin"

You'll find plenty of Info.

(as other people have said) If you bought from a vendor (like big 5) they've prob had it checked all ready.

[leedog]

I purchased from J&G sales. I would like to think they checked the rifles before selling them to the public.