Finnish M-39 reloading

[rmkey]

I know the 28/30 rifles are supposed to be .308 and the M-39s are listed as .310. Bullets available are .308,.311 and .312. Which to use if bore is actually .310?

I know Ruger barreled its mini-30 with a .308 barrel knowing everyone would use surplus .310 AK ammo.
I know the accuracy is bad and you have to wonder about pressure.

The AK bullets at 123grain .310 are too light for the 7.62x54r so whats the best answer?

 

[DaveInFloweryBranchGA]

"I know the 28/30 rifles are supposed to be .308 and the M-39s are listed as .310. Bullets available are .308,.311 and .312. Which to use if bore is actually .310?"

First, bore diameter is actually a misnomer. To decide what diameter bullet you need, you need to know the groove and land diameters, depending on wether you're talking jacketed or cast bullets. Land for jacketed, groove for cast.

"I know Ruger barreled its mini-30 with a .308 barrel knowing everyone would use surplus .310 AK ammo.
I know the accuracy is bad and you have to wonder about pressure."

Ruger barreled their rifles to SAAMI spec, which does not match the commie surplus ammo. They'll shoot good with American made ammo that's made to SAAMI spec.

"The AK bullets at 123grain .310 are too light for the 7.62x54r so whats the best answer?"

Cast your own to match the groove diameter.

regards,

Dave

 

[Clark]

My M39 has a hard time fitting Sierra .311 dia. 180 gr. SPT Pro-Hunter 2310 bullets in Lapua 7.62x53R brass into the chamber. Pressure is very high for the wimp load.

What does it all mean?
Those chambers are tight.

 

[U.S.SFC_RET]

DaveInFloweryBranchGA Quoted: First, bore diameter is actually a misnomer. To decide what diameter bullet you need, you need to know the groove and land diameters, depending on wether you're talking jacketed or cast bullets. Land for jacketed, groove for cast.

Dave if this is true then I have been sadly mistaken to believe that my bore on my mosin has been .311 when I want to shoot jacketed rounds. I certainly believe what you are saying and it sounds like a big relief to me. This deserves further study on my part.

 

[DaveInFloweryBranchGA]

The biggest thing to realize is a jacketed round doesn't spread and seal itself into the grooves nearly as extensively as a lead bullet would do. Along with that, the jacketed round, due to it's jacket, is not affected by gas cutting the way a lead bullet would be.

For a lead bullet, you want the bullet slightly over groove diameter, in order that it can obturate and seal the groove, thereby preventing gas cutting/melting of the lead as the bullet heads out the barrel. No gas cutting, no leading in most cases.

For a jacketed bullet, the above isn't a concern, but you do want the lands to grip the bullet enough to put a solid spin on it. I don't load very many jacket bullets any more and can't remember off the top of my head the best way to match it up, but I'm speculating that if the diameter is between the land size and the groove size, you should get reasonable accuracy results.

Regards,

Dave

 

[Bad Flynch]

>Which to use if bore is actually .310?<

Well, historically the bore diameter refers to the land diameter and what you have quoted is the groove diameter. The bore diameter for a 7.62 x 39 R is 7.62mm or, nominally .300". That is the way metric designations are done, the first number is the nominal bore diameter, not the groove. (do some correct metric conversions and you will comfirm this). Shoot the .311s; they will shoot just fine. You can try the .308s, too, but Lapua makes a nice .309" bullet that shoots very well in these guns.

Jacketed bullets normally fit the groove diameter, although exceptions exist. In addition, Europeans have a different idea of how bullets should fit than we do. For expample, our 30 caliber has a nominal bore diameter of 0.2995" and a nominal groove diameter of 0.03075" to 0.3085". However, Palma shooters shoot the 155 grain Sierra bullet, which is usually right at 0.3085" down tubes that are very tight: bores at 0.2985" and grooves that run as tight at 0.3065-0.3075". In Europe, the bores are pretty close, but the grooves run loose, and the bullets bigger. Typical 6.5s run a real 0.256" or so bore, but the grooves run as much as 0.267". In the U.S., some custom bullet manufacturers make "fatties," -- bullets that are purposely over nominal groove diameter so that one can try them and see if a certain rifle will like them, and some do. They are also very useful when a rifle's throat gets worn; the fat bullets can help make up the difference and extend the accuracy life of a barrel.

The only reason that you want a lead bullet over groove diameter, is that in the U.S. the throat is usually 0.001" or so over groove diameter and it needs to be filled in order to prevent leading from starting there (in the throat). Revolver cylinders are all over the place, but ideally would be 0.000-0.001" over groove diameter.

Ruger carbines shoot poorly, not because of the bullet diameter discrepancy, as is often thought, but because the bedding is lousy, and the peculiar type of gas piston is not conducive to accuracy. Here you have a stationary piston and a moving heavy cylinder, with a lot of slop in the bedding channel.

 

[DaveInFloweryBranchGA]

Flynch,

Thank you for your post. You reminded me of some stuff I'd forgotten and you taught me some stuff I didn't know.

Regards,

Dave

 

[Handgunr]

BF,

I use mainly cast in my revolvers and sizing to the cylinder mouths is preferred over the old "sizing to bore diameter" recommendations from days past. Many cylinder measurements can be .002-.003 over bore. and sometimes greater. If a cast round was sized to the bore, in the majority of guns, it would be hopelessly sloppy when exiting the chamber, and easily misaligned when connecting with the forcing cone.

Sizing to the cylinder chamber throats, but no more than
.003 overbore has been an absolute maximum limit. Lyman had recommended no more than .002 over, when I spoke with them last, and hinted that it was closer to .003, "but they didn't say it" (wink-wink).
Considering that most cast bullet mold companies recommend that sizing their "as dropped" bullets no more than .003 to prevent from destroying the bullets "best chance at accuracy", I can understand why many choose not to cast their own. Damn confusing for some.

Anytime I've cast, sized and shot cast bullets in a particular rifle, I've sized to .001-.002 over groove diameter. For instance, in an old .308, cast bullets sized at .310 shot very well for me as long as the pressures generated were within the workable BHN numbers of the alloy. I possibly could have sized fatter, but the bullet seemed to fit and function very well on paper.

Once pushed beyond those limits though, the ability of the alloy/bullet to recover was degraded, and it became apparent on paper.

Considering he hardness levels of jacketed bullets at approx. 40BHN, and the nominal BHN number's of usable alloys in rifles as being anywhere from lino at 21-22BHN, and heat treated alloys at 30-33BHN, it would seem that there's a little more latitude with sizing regarding cast bullets than jacketed due to the BHN variation.

I don't know how far, between the two, as I haven't tried to stretch it either way, but it would seem so.
Many cast rifle bullets carry a gascheck to consider as well.

Bob

 

[silverlance]

my own rounds that seem to work for me in my m39:

JMS brass
WIN LR Primer
WIN 748 2.5cc
Speer Hot Cor 150gr


lee loader

 

[Bad Flynch]

Handgunr,
>Many cylinder measurements can be .002-.003 over bore. and sometimes greater. If a cast round was sized to the bore, in the majority of guns, it would be hopelessly sloppy when exiting the chamber, and easily misaligned when connecting with the forcing cone. <

I understand the problem, and understand that there are many fixes out there. My most accurate loads for .38 Special use the Remington factory lead 148 gr HBWC, and I shoot them in an 8" Python. Those bullets run .360+" any day of the week and the groove diameter for this gun is 0.355." I have a couple of Smiths that like the same sort of load, but with the Hornady 148 grain HBWC and it is, nominally 0.357."

Some revolvers do, indeed, run very large in the cylinder throat. Colt SAAs come to mind and some of the Smith .45 Colts and .44s, too. However, Ruger .45 Colts have been, very often, undersized to as little as 0.449" for cylinder throats and sport a. 0.451+ groove diameter. There is no fix, really for a grossly over-sized cylinder throat, but at least I can ream an undersized one to a favored diameter. Still, even if the throat is over-sized, the barrel forcing cone can be set to about mid-way on the gage and will then handle the over-sized bullets needed for the over-sized throats.

Unsized cast bullets will generally shoot very well and one should not size them unless they need truing, and then just enuff to true them, or unless the loaded ammo with the larger bullet will not chamber.

Undersized lead bullets, smaller than the throats, generally mean leading trouble, but not invariably so. If one shoots a really hot load and the bullet hardness allows them to bump up to throat diameter, sometimes they will work just fine, sometimes not.

50-70 years ago, Phil Sharpe did experiments with over-sized bullets. The bullets were over-sized in steps to the point where the bases would acquire fins from the metal displaced from sizing and engraving in the bore. His conclusions were that fins are detrimental to accuracy, generally, so dramatically over-sized bullets simply can't be that good.

I'll very much agree that there is more latitude with cast bullet size than with jacketed, but my interior ballistics program, QuickLoad, allows for over-sized jacketed bullets and does not complain until it gets to a certain point. Richard Lee, in his loading manual, states that over-sized copper jacketed bullets, even those that are markedly over-sized, will only raise pressures by what seems to be a modest amount compared to the total of a high pressure load. The QL program gives more credence to core hardness, jacket hardness/temper, and bearing length than to bullet diameter, and that follows what the NRA found out many years ago.

 

[Handgunr]

BF.....

My most accurate loads for .38 Special use the Remington factory lead 148 gr HBWC, and I shoot them in an 8" Python. Those bullets run .360+" any day of the week and the groove diameter for this gun is 0.355."

Funny you mentioned that about your Python.......back in the old days of cops carrying revolver's (yeah, I'm that old) I was the range instructor & armorer for my dept.

After having a timing problem with one of the deputies guns (a python), I had to contact Colt for shipping and packaging information and I got into a long discussion with the Rep....

It's amazing at how tight the bores were on them (.3545-.356), and then he described how they run a carbide ball through the cut rifling to smooth it. I thought it'd destroy the rifling.

Top notch revolver.....the fit & finish was always "grade A" on them, but a steady diet of magnum loads seemed to loosen them up quick.

On another note, you brought up a point I really didn't consider, and that was since a hardcast lead bullet, with a consistent hard alloy throughout, might be a little more detrimental than even a jacketed bullet with a pure lead core, considering that the jacketed bullets have the harder shell with the soft inner core. It might make a big difference in reference to shooting oversized bullets.

Bob