Help decipher a chamber/throat/bore cast

[texassako]

I have decided to get serious finding a cast load for my Finn M28-76 ; so I took a cast of the should, neck, throat, and bore. A few other pertinent details: chambered in 7.62x54r, 9.5 twist, .299"/.308" bore, 26" long barrel, target rifle so I usually just single load. It has me confused because the rifling starts over 1/2"(.65") from the neck. The throat tapers from .314" by the mouth to .308" at the start of the lands, which take about one more inch to reach their full .299". It sure seems like a lot of freebore to me, but the Finns have a lot of experience making Mosins shoot well. I attached a pic of the cast with 2 dummy cartridges with a 311334 and a 311284. The front driving band at .311" is what stopped them from falling deeper when I was trying to establish OAL. If I went down to .309", I could seat the 31128 on the last band probably. Experts, please weigh in with some opinions, ideas, or even just a good luck. I am thinking I might need a longer boolit.

75755

[chboats]

I agree with excess650. a tapered boolit would be my first suggestion. Actually my first suggestion is to try what you have to see how they work. I would not size the whole boolit to.309, maybe the first band.

This is the boolit that I use. I ordered it .002 less than the diagram. With my alloy it casts at .307 at the nose and .314 base bands

http://www.accuratemolds.com/bullet_detail.php?bullet=31-195B-D.png

Carl

[runfiverun]

the one ch linked you to should do the job.
use his picture and add in YOUR measurements to order the mold.
I have that same mold and sized to 314 i can seat the gas check in all 3 of my argies case mouths and close the bolt.
you have a moderate throat compared to them.

[john hayslip]

The long throat probably made sense to the Finns as they probably had a ton of captured Russian ammo with the larger diameter bullet. The long throat would help with the excess pressure caused by putting a 311 bullet down a 308 bore.
When my son graduated from Texas A&M I had a 7.62x39 left handed bolt gun made up for him by a friend. We started off with a 308 barrel and Chinese ammo would lock it up tight. Found a 311 bore off an old American Enfield and all excess pressure signs went away. He's got both barrels so he can pick and choose.

[texassako]

What is the inside diameter of a fired case neck? Hopefully in excess of .313"?

For sure it has a deep throat, and IMO, if you really want accuracy, you should have a tapered boolit mould cut to fit, OR get a tapered die made so as to shape your boolits to fit. The boolits don't need to be any longer, but I would be working to keep that throat sealed.

Inside of a fired case measures at .315". So I need a .314" boolit(or at least the base of it) to give me a thousandth over the .313 and still have a thousandth to release it? I have an unused Lee .314" push through die laying around somewhere and the 311284 drops at .314". Give it a whirl sizing the top band to .309" and leave the rest at .314"? The only .30 cal sizing dies I have are Lee .309" and .314" and a .311" in the Lyman 450. I was already considering a custom mold for this one since the 311334 and 311284 are just short term loaners.

[texassako]

Sizing the boolit at .314" keeps it from chambering as it looks in the picture above. I have to seat it in where the top band is mostly in the neck and the check is below the neck. Maybe I will try a couple of the 311334s at .314" since they keep the check in the neck. I think I will be ordering the mold chboats referenced and run seconded soon once I measure on the cast where those bands would be and measure them.

[tomme boy]

How is the barrel marked? Some of these are made to use the Russian ammo and some are not. The later years 68-72 seem to be able to shoot the Russian stuff. Some are also marked with the D stamp. If it is not, it should have a shorter throat.

[texassako]

It is not marked as a D chamber. It is an ASEV1 barrel dated 1974. I have not seen a cast of a D-166 chamber to be able tell if it is just unmarked.

[texassako]

I was just trying it all at .314" to see. It was a pain trying to size the top band in the Lee sizer. I will try flipping it upside down and running just the top band down into my lyman .311 die since I know that fits seated with one gg in the neck sized entirely to .311".


I'm not suggesting that all of the driving bands be sized .314". Rather, the portion in the case, and perhaps a bit more be .314", and the remainder can be smaller. The idea is to keep the powder gases contained behind the boolit, hence the "fat base" to seal the throat. Ideally, at least a 2-diameter boolit for alignment and seal.

I have a friend with a Rem700VS in 308 that has a .313" throat and long enough that the 311284 sized .311" on the front band will keep the GC in the neck. It shoots tiny groups, and judging by the "tapered leade" that you have ahead of your case neck, your rifle has the potential to be a real shooter.

Wanna go cheap on a mould? Lee CTL-312-160-2R (170gr w/gc) and S&L at .314".

[tomme boy]

Well if it is not D marked, then it is just been shot A LOT. Take a look at this drawing. I made this one for one that had a worn, but not shot out. I have shot this in 2 Mosins and a P14 303 Brit and it has worked great. If you want, I can send you some unsized boolits to try. Send me a PM if you do. I can also size them 0.313" or 0.314" if you need it.

[tomme boy]

http://www.accuratemolds.com/bullet_detail.php?bullet=31-215B-D.png

Forgot to add link

[texassako]

I don't have a bore scope to check erosion and being a milsurp you just never know. It is one of a few left hand stocked with the scope mount; so it could have sat unused a lot and made that way or been been on the range every day and used by every lefty in the Finn military.


Well if it is not D marked, then it is just been shot A LOT. Take a look at this drawing. I made this one for one that had a worn, but not shot out. I have shot this in 2 Mosins and a P14 303 Brit and it has worked great. If you want, I can send you some unsized boolits to try. Send me a PM if you do. I can also size them 0.313" or 0.314" if you need it.

[runfiverun]

tome's overgrown LEE would be fairly close too.
you could manipulate his numbers as needed.
just make the changes on paper and have his drawing handy when on the phone to tom.

[chboats]

If you are going to order the 31-195B from Tom you might want to communicate with Tom about the size. Tom designed the original for me but when I got it the boolits, with my alloy of WW+ tin, dropped at 310 nose and 317 base bands. This was actually good for me because it fit my 7.62x54r just great. I ordered the mold for a 7.65 Argentine but were too big. I had Tom reduce reduce all dimensions by .002 and it worked great. I ended up with 2 molds one marked 315 195 and the other marked 313 195. Both are great molds for different guns.

Carl

[texassako]

I really want to thank everyone who chimed in on this and those who posted all the threads I could read about 7.62x54r cast loads. I think the 50 yard initial test load results speak for themselves. I sized these .314" in a Lee push through, then sized the top band .311" on the 311284 upside down in the Lyman 450, and tumble lubed with 45/45/10. Only some WC860 311284 loads had open groups, but they burned clean. I think it really likes the 311334 in these low speed loads, and it drops at ~.311" so only the gas check is .314". I guess it is fine tuning time at 100 yards with the 311334 and I even found some Accurate 5744 locally to add another powder to try. It has been tough getting used to the odd reticle(1 moa circle inside a 3 moa circle above a vertical post) in my Kollmorgen 4x scope plus it was slowly shifting in the rings, but you can't be very choosy when needing a 26mm tube scope. The odd 36 count cartridge boxes I have are the reason most are 4 shot groups(9x4 grid in them).

765557655676557

[tomme boy]

Have you tried the ones I sent you yet?

[texassako]

Have you tried the ones I sent you yet?

They are in the first picture marked 31-215B on the top, and did almost as well as the 311334 at 12 gr Unique. I had to seat them pretty deep since the nose was just a bit to fat to far out. I only used some of them since I am trying to compare designs and want to try a range of load levels. I found a pound of 5744 at Cabela's today, and figure that is a good step up from the Unique loads.

[tomme boy]

I really like that powder. Only the price keeps me from buying it. 20-22 grs seems to be where it ends up at in a few different rifles for me.

[texassako]

I did a side by side test of the 311334 sized .314" with the top band sized to .311" and the whole thing sized to .311". The .314/.311 was the previous winner at 50 yards. They do not reach into the rifling, but the top band is seated touching the throat. I was using 5477 and used 3 different charges just in case the different sizes preferred a slightly different charge. The .311" sized bullets shot the same or smaller groups with the best in the pic(hard to see 2 shots above the red). Very gusty 10-20mph tailwind yesterday and my tremor was acting up more than usual, which caused the flier. I think next up is to go back to the more accurate 11 gr of Unique since I found some more and test with Dacron on a calmer day.

83999

[MtGun44]

Sounds like a normal, but worn throat to me. It is a 75 year old rifle, who is shocked
that it has a worn throat?

Bill

[texassako]

Sounds like a normal, but worn throat to me. It is a 75 year old rifle, who is shocked
that it has a worn throat?

Bill

It was rebuilt by the Finns with a new barrel among other alterations in 1976. I don't have a bore scope, but it was designed to fire a .311" bullet in a .308" bore with a long cone shaped throat to the rifling to smoothly squeeze those bullets down.

[mikeym1a]

Take a look at this one. JTKnives made it, and it might meet your needs. He made them in .311, .316, and .324. It is a bore rider that may work for you, provided he has any left over. They are really nice molds.


http://castboolits.gunloads.com/showthread.php?206520-HM%B2-30-31-cal-160gr-6-CAV-Ed-Harris-Design

[texassako]

I think I finally found a bullet with a good fit. The NOE 311331. Seated to 3.110" COL on the bottom driving band, it is the first I have tried that actually engraves the rifling. I wonder what it would do with a long 240+gr bullet since it would fit?