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customaquatics

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a youtube vid said the bore diameter of the rifle he was shooting was a .308?
"@ImWatchinTheTube They were designed to be .3105 in diameter, but during the mass production during the war some were as small as .309 and some as large as .313.  It is always best to slug the barrel, or, experiment with what sized projectiles work best for your rifle. In this particular rifle, .308 diameter projectiles work the best, while in my other 91.30, .311 works the best.
mag30th 2 months ago "
what's up is this true?
 
A basic post introduction might be of some assistance here.

"Today, I was on you tube searching for "XYZ" rifles and came across this video..."
 
It was a Russian 91/30, formatting sort of hid that crucial fact which wasn't disclosed up front. 99% of the time when the bore diameter of European .30 caliber rifles is discussed the bore has not actually been measured and 99% of the rest used cerrosafe without reading and following the instructions. The internet is superbly effective at perpetuating idle speculation as fact.
 
Well, the "correct" caliber of the Model 91 M-N is "three lines", and a Russian "line" (liniya) was officially set at 1/10 of an English inch. So, in theory at least, the Model 91 and its successors had a bore diameter of .300".

But that is certainly subject to production tolerances, and those can be large even with the best machinery and most skilled labor, not always characteristics of Russian manufacturing in the pre-revolutionary period and during the crisis in WWII. In addition, those rifles did not always receive the best care and few have new bores, making slugging bores somewhat of an adventure.

Just FWIW, specs for U.S. .30 rifle barrels through WWII were:

Bore - .2995"-.3015" (nominal .300")
Groove - .3075"-.3095" (nominal .308")

Jim
 
Not to mention the number of people on the internet who will gladly explain the difference between "clip" and "magazine" but will steadfastly call the groove diameter of a barrel the "bore."
 
Well, a clip is what I get at the Barber's, and a magazine is what I read while waiting for my clip

But on a serious note...Jim K., great insight on the Russian method of determining the 91's caliber
 
I have loaded for .311- .312 barrels for years and rarely used other than .308 bullets. Crazy as it sounds, most shot better with the undersized bullets. As far as shooting oversize bullets in a tight bore, P.O. Ackley did experiments with that and as long as the neck and bullet were loose enough in the chamber and free bore there was no problem.
 
they used the same basic dimensions for the 3 line mosin nagant as the british did for the .303 enfield. manufacturing has it different by period of construction.
and the finns made it even worse when they rebarreled a large number of captured rifles with a necked down cartridge using that .308 bullet.
 
While some folks will have hysterics when I say this, the fact is that .003-005" difference in bullet diameter vs groove diameter just doesn't matter that much in terms of pressure or often even in accuracy. Unless the jacket is very heavy, a small diameter bullet will upset. A larger one will just squeeze down some. When pressures reach into the 50k psi range, the bullet is forced to conform to the barrel.

Where diameters do count, though, and where folks who play with oversize bullets need to be careful, is in the chamber neck diameter. When a rifle cartridge is fired, the first thing the pressure does is to force the case neck to expand out into the chamber neck, freeing the bullet and leaving it floating in gas, held by its own inertia.

If the chamber neck is meant for, say, a .308" bullet, and a .311+" bullet is loaded, the case neck is larger and there is no room for it to expand; that means the bullet is held solid and cannot move, causing pressures to surge. That, not the bullet diameter, can create real problems, and was the actual cause of high pressures when the 8x57JS ammo was fired in the old 8x57J chamber, not the .005" difference in bullet diameter.

Hi, Newton,

Just curious, but how do you know what the Russians did or intended to do decades ago? When they had settled on a .300 bore, how do you know they decided to ignore that and use a .303 bore? The good bores I have slugged seem to indicate that they at least tried to maintain 7.62mm nominal and their military bullets run .3075-.308", just about the same as our .30 and 7.62 GI bullets. If they intended to go to .303 caliber, one would think they would produce .311" bullets.

Jim
 
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One thing that complicates this issue is that the Russians themselves used and use numerous types of ammunition; the initial type "L" ("legkaya"/"light") M1908 round used a lead-core spire-point bullet with a deep base hollow, that would "bump up" on firing to fill whatever bore diameter it was being fired in, and even the later "PS" ("pulya stal"/"steel bullet") steel-core bullet has a thin lead sheath that allows a certain amount of expansion. For ammunition where accuracy is critical (sniper rifles), they still load the "LPS" round ("legkaya pulya stal"/"light steel bullet") with a two-piece core, having a soft lead rear core with a recessed base and a steel forward core.
 
Many US bullets will also upset to some extent, but no designer would depend on that for accuracy. That aside, none of the Russian bullets I have seen miked out as anything other than within normal tolerances for a .308" bullet, that is to say for a rifle with a .300" (7.62mm) bore diameter, .308" (7.82mm) groove (again with allowable tolerances).

Some people say that the Russians used .303 bullets (.311"), and others contend they even went as large as .315" or .320"; I simply don't believe that based on what I have seen. I have little doubt that in the WWII emergency, tolerances may have been relaxed, but that much?

Jim
 
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