Mosin Nagant M39 bullet size?

[Tuzo]

Which diameter bullet for my Finnish 1942 Mosin Nagant 7.62 X 54R?

Slugged the barrel and .310" is the result. Various sources - citing Wikipedia - state this rifle barrel is .310" after 1939 and .308" prior to 1939. So far so good. Wiki also states to handload this cartridge with .308". Other sources state .308" to .311".

This rifle shoots very well. With mixed lot surplus Russian ammo I was hitting a 10" diameter steel plate at 100 yards and iron sights with every shot. The bullets were either .308" and .311".

My concern and question to the the forum is which diameter bullet to load for safe and accurate ammunition.

[kostyanj]

If barrel slugged at .310, go with .311 bullets. You want bullets that are .001 larger than bore.

[JD0x0]

You're better off going slightly oversize rather than undersized. .310, .3105, and .311 should all work.

[skizzums]

btw, if your nagant is a good shooter with the surplus, your going to be amazed at how well it shots with a properly put together round. it's my favorite iron sight gun to shoot, especially with a good handload. .. .311 is the way to go.

[kostyanj]

I have a shameless plug now. I have some .311 bullets for sale if you're interested, PM me.

[Clark]

I know someone who is 63 and been hunting with one Mosin Nagant or another since he was 14.

Every year he shoots a buck with his Weatherby out with the guys. But late in the season he shoots a doe with his Mosin Nagant, all by himself.

He got me started using Sierra 180 gr .311 bullets 13 years ago.



Pro Hunter model 2310

https://www.sierrabullets.com/store/...dia-180-gr-SPT

I have lots of Mosin Nagants, but only one M39.
It is a Sako barrel.
I put a scope mount on it and welded the bolt handle.





The Over all length is 3.1".
I work up a load with 4895 until the bolt is sticky and then back off a safety margin ala Vernon Speer 1956.
The M39 chamber neck is 0.340", which can be a problem.

I like the Lapua brass the best.

[res45]

My concern and question to the the forum is which diameter bullet to load for safe and accurate ammunition.

Many handloaders find that the .308 dia. bullets shoot just fine in the .310 groove bore Mosins. Using bullets that are larger than the groove dia. especially if you at Max. load/pressure can cause dangerous pressures rises.

I have some nonshootable surplus 1936 Finnish VPT 53r ammo and it's loaded with .308 dia. bullets.

[Clark]

res45
.. Using bullets that are larger than the groove dia. especially if you at Max. load/pressure can cause dangerous pressures rises.
..

So it would seem intuitively, but per my reading and per my experience it is not the case.
To prove it, Ackley shot .323" bullets in a .308 groove bore.
P.O. Ackley 1966 "Handbook for Shooters and Reloaders Vol 2" chapter 7
"additional pressure tests":
"..30 cal barrel pressure barrel was fitted to the test gun, but the neck and throat was enlarged to accept the 8mm bullet, with the bore remaining the standard 30 caliber. A Remington factory 30-06 cartridge with the 150 gr bullet had been tested and previously gave 57,300 psi, for a velocity of 3030 fps. The the bullets were pulled from two more Remington 150 grain cartridges and were replaced with 8mm 150 grain bullets. To everyone's surprise, although the velocity was rather erratic, these loads averaged 2901 fps, with a pressure of 40,700 psi."

The only way I can reconcile that is that the added bullet swaging pressure is not concurrent with the peak pressure, so the pressures do not add.

Meanwhile, a tight neck that pinches the bullet and adds more static friction before the bullet can start moving, delays the bullet and makes huge pressure spikes.
That is why I mentioned my M39 chamber neck size.

[Tuzo]

Thanks for all the good information.

Ordered 60 rds of Prvi Partizan ammo and 0.310" Hornady expander plug from good old Midway USA. My Hornady die set includes a 0.308" expander plug. The ammo is reusable brass, boxer primed for future reloading. Will experiment with .308" and .311" bullets in these reloads.

The brass I have now is surplus Berdan primed stuff that is mostly damaged and too dangerous to shoot. Had a 2 second hang fire last Sunday with a good number that did not fire. Sad to have to destroy about 150 rounds.

By the way, the rounds that did fire were very accurate 149 grain FMJ steel core with the slightest boat tail taper.

[kostyanj]

Tuzo, I got your pm but am having problems replying. I have 125 gn Sierra Spitzer Bullets.