Mosin Nagant Bore Size

[dale2242]

I recently slugged the bore of my Mosin Nagant 7.62 X 54R.
The slugged out at .314.
That sure seems big to me.
I understand that most slug out at .310-.312.
Is .314 bigger than normal for this caliber?...dale

[Hickory]

Most war clubs, especially if they are built during the war, will not be of the best construction or the tightest dimensions. These firearms are built to safety put a bullet down range with the hopes of killing or wounding the enemy.

[dragon813gt]

Not bigger than normal. That falls in the range of a normal bore size. If you don’t have a mold that casts large enough there’s plenty of options out there. Same thing for sizers.

[LAGS]

I have had MN's with Good barrels that have a groove diameter as high as .316.
I just shot properly sized Cast Boolits in them, and they had very good accuracy.

But check the neck size on the case when loading Oversized bullets.
You don't want the bullet to expand the neck out, so it is a Pressed fit when you chamber the round.

[truckjohn]

I recently slugged the bore of my Mosin Nagant 7.62 X 54R.
The slugged out at .314.
That sure seems big to me.
I understand that most slug out at .310-.312.
Is .314 bigger than normal for this caliber?...dale

That's normal.

I have slugged hundreds of Mosin Nagants.
0.314" is by far the most common on regular infantry rifles with good looking barrels. I have seen worn rifles up over 0.318".
0.312" is the minimum spec groove diameter - and the dimension that most MN sniper barrels were made to. You will occasionally find an infantry rifle with a 0.312" barrel - but it's like 1 in 100... It's fairly common to see ex-snipers in this range though.

Of the hundreds I have slugged - I have never seen a single Russian Mosin that slugs below 0.312". Finns - yes...

I see this same thing stated with Enfields as well.... Oh - they have 311 barrels.... Nope - the military spec was a 0.314" groove diameter....

It's fairly easy to make a slug read 0.311".... Just use your micrometer like you are measuring steel, give it a couple clicks, and it will mush down the slug a few thousandths.

[truckjohn]

But check the neck size on the case when loading Oversized bullets.
You don't want the bullet to expand the neck out, so it is a Pressed fit when you chamber the round.

Absolutely this is a common issue with Mosins. They often have very tight chamber necks. These can hang up and jam or cause severe pressure problems with bullets sized to fit the barrel.

Ironically - 7.62x54r is the only caliber I neck turn cases for. This is the reason.

[nagantguy]

314 is “normal “ I’ve personally owned as large as 316

[samari46]

Finnish moisins as a rule have smaller dimensions. Basically they used the action and made everything else. My Finn model 27 slugs out at .3115". My Lyman 314299 casts at .303-304 on the bore riding section and the body casts at .314. Pretty old mold as it's about 30 years old. liked it so much bought a second one in case I ever screwed the first one up. Still has the rust preventative paper on it and just checked it out and looks brand new. Frank

[Bookworm]

I have a 1931 Hex receiver 91/30. The bore slugs at .315". I shoot NOE 316-213-RN sized to 316. The best 100 yd, 10-shot group I've fired was 2.75". The barrel is dark and pitted, so I'm pleased with what I've got.

As brought up earlier, the problem comes in when trying to chamber fat boolits. The chamber specs call for a .338 neck. Using a 316 boolit, I have to neck-turn brass to .010" to get these rounds to chamber safely (.316+.010+.010=.336). For some reason, WIN brass is the brass most needing trimming.

[tomme boy]

I have one I kept that it 0.312" that is a 91-30 dated 1943. It has a perfect bore and grove. I have had many others that were 0.311"-0.315" that were near perfect to almost a smooth bore. Most were in the 0.3125" area.

The one I kept has the least amount of rounds through it as I can tell by looking at the bore and throat through a bore scope. I had my C+R lisc at the time and I ordered about at least 100 of these rifles and I went through and shot and sold of the rest except this last one.

I had a theory on the variation of bore diameters. They started off with a large button that cut the barrel around a 0.313" and as it wore down and was sharpened again and again it ended up at 0.310" or so and that was why the diameters are all over the place.

[3006guns]

I have one I kept that it 0.312" that is a 91-30 dated 1943. It has a perfect bore and grove. I have had many others that were 0.311"-0.315" that were near perfect to almost a smooth bore. Most were in the 0.3125" area.

The one I kept has the least amount of rounds through it as I can tell by looking at the bore and throat through a bore scope. I had my C+R lisc at the time and I ordered about at least 100 of these rifles and I went through and shot and sold of the rest except this last one.

I had a theory on the variation of bore diameters. They started off with a large button that cut the barrel around a 0.313" and as it wore down and was sharpened again and again it ended up at 0.310" or so and that was why the diameters are all over the place.

I think you're right. I had a very dear friend, now passed on, who was Russian and fought with the U.S. Army. He told me that the LAST thing the Soviet arsenals were worried about was supreme accuracy and their use of tooling reflected that. Speed and production was everything, and if you think about what those people went through it's amazing that they kept everything as close as they did!

[arlon]

They run quite a range especially with the Finnish rifles thrown into the mix. I have a bunch of them with bores ranging from .309-.318.

[ShooterAZ]

My MN slugs at .3125, and I use boolits sized to .314 in it. You should be able to use a .315-.316 sized boolit, as long as it will chamber. Mines a really good cast shooter, despite having a typically horrible trigger.

[dale2242]

I have been asking in S&S for some .315 boolits to try before I buy a new mold.
I would like them sized and lubed. I do not PC.
The chambering issue is what I am concerned about...dale