Specs on Mosin Nagant go/No-Go gages

[Mesa]

Does anybody know what the specs are on Go/No-Go/Field headspace gages for 7.62x54R (Mosin Nagant)? I want to make myself a nice set of stainless steel gages.

Mesa

 

[Mesa]

Somebody break out a micrometer

Hey don't all of you jump in here at once!

Will SOMEBODY, somewhere, break out a micrometer or caliper and measure a set of gages for me?

Mesa

 

[4 eyed six shooter]

It's not so simple to just take measurements. The front of the guage requires it to be a specific angle, it's not just the how long the guage is and the diameter. The angle determines where the front of the guage hits the front of the chamber. If the angle is not exact, you cannot determine the correct length of the guage. As you are dealing with just several thousanths of an inch between go and no go, making one yourself is not an easy task. Better to buy the guages and make another tool instead. All of this is not to say that you are not a good machinest, it's just getting the exact measurements that is the tough part.
Good shooting, John K

 

[Jim K]

I checked for some info on the 7.62 rim thickness and can't find anything.

Note that the front of the chamber is not involved in headspacing that rifle, since it uses a rimmed round. The headspace gauges are only little stubs less than an inch long.

See:

http://www.russian-mosin-nagant.com/headspace.htm

for a good discussion, but, alas, not an answer to the question.

Jim

 

[Jim Watson]

Nonte says the rim thickness of 7.62x54R is .064".
I haven't a clue as to what the tolerances are for gauge manufacture. Remember, the Russians established them in 1891, it is hardly a SAAMI spec. Brownell's sells Clymer gauges for $20.

Read Hatcher and Ackley. Headspace measurement for use of factory or arsenal ammo is overrated. It has to be way off to give trouble. Handloading is a different proposition because you can keep running the shoulder back and forth.

 

[4 eyed six shooter]

Jim, Thanks for the correction. For whatever reason I was thinking of the 7.62 X 51. Maybe I should try sleeping instead of playing on the net. Making the guages should be an easy job providing someone has the correct rim thickness to give to Mesa.
Sorry, but I don't have a set to measure either.
Good shooting to all, John K

 

[Jim K]

Hi, Mesa,

Please permit me a little tutorial on headspace and gauges.

Headspace is probably the most discussed and least understood of all the topics on gun forums. It is involved not only with rifles (and handguns and shotguns as well), but with ammunition, and with manufacturing tolerances in both. For most rifles, the headspace will be perfectly fine. I once checked a couple of dozen old Mauser 98s and not one had a headspace problem. Further, I once took 6 or 7 Mausers, from 5 countries, swapped bolts around several times, and all combinations were OK for headspace (field gauge).

My advice is that unless you are rebarrelling a rifle don't worry about it. Shoot the rifle with a string or simply by keeping your head back for the first shot. If there are no problems, just shoot the rifle.

But if some discussion will help, I will provide it. The problem is that determining headspace measurement involves cartridge specs, and to see that, we need to look at what the gauges really do.

The GO gauge ensures that the longest cartridge (thickest rim in this case) that is within spec will fit into the rifle.

The NO-GO gauge ensures that the shortest cartridge (thinnest rim) that is within specs will be OK. This is the minimum spec for the cartridge plus a factor to allow for normal case setback. (It is this plus factor that makes the NO-GO longer than the GO even though it is testing for a shorter case.)

The Field gauge ensures that the shortest cartridge (thinnest rim) that is within specs will not be dangerous after the rifle shows wear and use.

The GO and NO-GO gauges are used at the factory and when rebarrelling a rifle or replacing a bolt. The Field Gauge is employed with used rifles. (A rifle may fail the Field Gauge test and still be fine with medium or long ammo, but a soldier cannot be sure what ammo lot will be issued to him.)

In short, unless something looks suspicious, like a sporter that has been rechambered, I just shoot the rifle and let it tell me if there is a problem.

Jim

 

[Mesa]

Jim, there is a problem with one of my Mosins. I have two M44's and one 91/30 that all shoot some mil surplus Russian ammo with no problems at all. However, I recently bought an M38 and after firing it, the bolt is nearly impossible to open. In fact, it takes pretty much everything I have strength wise to open it. That's why I want to check the headspacing on the rifle.

Mesa

 

[Dogsoldier]

Mesa,

Use this down and dirty trick for headspace at your own risk. On the rifle that is giving you problems, take a cartridge and place a piece of masking tape caross the base and rim. Do not wrap the rim. Chamber the round, the bolt should close. Now, add another piece of tape, the bolt should close again. Add a third piece of tape, the bolt should NOT close. bviously if the bolt closes or doesn't close when it is suppose to, you have problems. I have seen a few Mosi's that have had worn or pitted chambers that caused the sticky case syndrom. Of course, with a pitted chamber,someone usually gets in there with a dowel wrapped with sandpaper and makes matters worse.

Good luck.

 

[Jim K]

Hi, Mesa,

I had the same problem with an M44 with East German steel case ammo. Terrible! Finnish and Russian ammo gave no problem at all. I don't think the problem is headspace, though. If I get a chance, I'll try to figure it out, but was driven from the range by a downpour and gave up for that day.

Jim

 

[drannor]

I'll second Jim's statements.

I purchased some Sellier & Belliot 7.62x54R for my M38 carbine and I couldn't get 5 rounds thru the thing without it locking up so tight I had to brace the rifle against my FOOT to get the action open. Visions of dead Red Army troops in various frustrated poses with locked up rifles came immediatley to mind. I just couldn't believe this was a common occurence!

I switched to some inexpensive Russian ammo and this problem disappeared. Same goes for my Finnish M39 Nagant. If you like Mosins I HIGHLY recommend the Finnish rifles.

Barnaul Ammo
That's a link to the Barnaul ammo I've been using. 204gr boat tails in a berdan steel case. Less than $5.00 for 20 rounds. I've gone through about 100 rounds of this stuff without issues so far.