Help with my MN 91/30 Sticky Extraction

M

mj246

New member
I know this topic comes up a lot, but I haven't found a good amount of detailed info on it.

So the bolt on my 91/30 cycles smoothly both without ammo and with a-zoom snap caps, but I had sticky bolt/extraction after firing with steel cased surplus ammo (unknown country/manufacture). I'm pretty sure it's not extra cosmoline coming out from the heat because it started after the very first shot. I don't think it would be the extractor itself if it works with the snap caps. What might be causing this? and should I try a different ammo or send it to a gunsmith?

If it helps any, my brother used his calipers to check the dimensions of a fired case against the snap caps and unfired brass, and the fired case is 0.1 mm thicker right above the rim (which I would expect from steel cased ammo) while the snap caps have slightly thicker rims. Could either of these explain the problem and how would I fix it?

Thanks in advance for any answers and advice.
 
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If you're sure you've removed all the cosmoline from your gun (especially the chamber/throat area) then I would try a different type of ammunition. Mine was sticking with the lacquered coated type and when I tried the copper washed ones, the problem went away. Don't go buying a whole case of any surplus ammo till you find one that your gun likes. I wouldn't attempt any "home-style gunsmithing" like those you-tube vids till you've tried the ammo switch. Good luck.
 
Edit...

The case being thicker above the rim could indicate a headspace issue- and would obviously be the cause of the hard extraction. 1 mm. in thickness is a mile...and I suspect that since the 7.62R headspaces off the rim, that if there were excessive headspace to the bolthead, that's where the brass would "flow" and create the excessive thickness.

I don't shoot steel case ammo, and I know it does not return as closely to unfired dimensions as brass- but that still seems like a lot.

Get a no-go gauge and check it before going further. If it bears out, you may be able to solve the problem by swapping out the bolthead (I've done that)...
 
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Thanks for the advice. Just to be clear it is 0.1 mm (1/10th mm) difference in thickness, not 1mm. Is there some way to check the chamber without the go/no go gauges? Brownells seems to charge $62 for a set in 7.62x54R and that is too much to justify on a $120 rifle that I don't intend to get another of in the same caliber.
 
Take a 20ga cleaning brush, chuck it and the rod in a cordless drill and clean the chamber with it. Chances are your chamber is just still full of dried cosmoline that is gripping the fired case. Sticking cases is usually due to a cruddy chamber on a Mosin.
 
The bolt runs fine with unfired ammo, and sticks with the first round fired- before it gets hot. Not likely to be "sticky bolt" IMO.

mj246...

This is really "unscientific"...but, some guys place two layers of masking tape on the back of a fired cartridge to simulate a no-go gauge.

If you try it, and the bolt closes easily and fully- you probably have an issue.

If the bolt closes only about halfway and you encounter additional resistance, headspace may not be the issue.

To be clear- I would recommend this only as a quick possible indicator- and follow up with a no-go gauge.
 
So I took it out yesterday and it was cycling better with the same ammo than the first time, great with a different steel cased surplus ammo, and flawlessly with some brass case Winchester ammo. I didn't see any signs of case bulging or pressure problems with any of the ammo this time around, so I'm definitely thinking that 1) the chamber wasn't as clean as I thought the first time I used it and 2) it doesn't seem to like that one kind of surplus ammo that I got from my brother's friend.

Thank you all again for the input. By the way, accuracy is pretty good at 75-100 yards. going to have to try it from longer distances in the future.
 
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