My throat slug #'s-What do they tell me?

[okksu]

A Finn M-39. My first CB attempt was not good, lots of leading using the below CB & 15-16 grains of 2400, w/o a gas check Going back this time with a GC and similar charges of 2400.

I did a throat slug with these results:
Case mouth OD = .337 Hornady Manual case spec = .336
Muzzle case neck OD= .339 " = .337
Shoulder OD= .461 " = .457
Throat, muzzle end= an oval, .311-.312
Throat, breech end= an oval, .313-.314
Throat length (top of case to start of lands)=.526.
Rear of Case to start of lands= 2.649

The barrel slugs .300/.310

I'm working on loading a Lee .312 C E Harris style Boolit, GC'd and sized to .312, 156 grains. (I could leave it mold diameter @ .314)

Currently, my seating leaves .690 exposed boolit, which is seated to just behind the crimp groove, & on the front driving band.

boolit is .309 dia. in front of the crimp groove.

It is .391 from the case mouth to the point where the boolit gets to .300 dia. I could stretch that out to .423 or so IF I seated on the rear driving band.

With the current seating, Base to a .300 dia on the boolit is 2.445, so if I went to the rear db it could go out to 2.477

Current overall length is 2.765, and so that could go to around 2.792 if that would help. Hornady Max. COL=3.048

I am concerned that my boolit fits OK diameter wise but is too short for the throat in this rifle, even if I tried to seat only to the rear db. Your Thoughts?

[geargnasher]

I figured the boolit you were using would be way too short for that gun, but it will still shoot, and might shoot better than you think it will if you get some other things ironed out.

I've only played with one 7.62x54R and it was a Russian M. N., it had a HUGE throat and a leade that seemed to go halfway up the barrel. I ended up using 180-grain Lymans (don't remember mould #, but it was a Loverin FN and was advertised at 183 grains according to my notes from high school) and seated them to engrave, which put the gas check right at the base of the cartridge neck. I'm sure they wadded up a bit like a noodle between the case mouth and the rifling when fired because the 311" boolit had to traverse a big gap unsupported, but they were minute-of-6"-pipe-gong at 80 yards, and were great fun to shoot.

I think having a go again with the 2400 and some gas checks this time may get you somewhere, I would keep sizing to 312" just like you're doing, use some sort of solid lube, and let us know how that works. Report back, and based on results I have a trick or two that may help if needed.

Gear

PS how does the chamber neck of your loaded ammo compare to the chamber neck of the slug?

[okksu]

Loaded Round: muzzle end of neck = .332 -334(ovaled) vs .338 on the slug's neck (I picked up .001 this time); Load's Breech end of neck= .333 (top of the shoulder) vs. . 339 on the slug.

Noticeable expansion in the loaded brass starting @ .015 above the shoulder. I used an expander die to flair the case mouth and get the boolit started in the case. Isn't a sharp edged crease or wrinkle, just flairs out by .002 over its .015 width. The upper end of the flair is .252 from the case mouth. The boolit is seated @.290, so the flair is starting just about where the top of the GC is inside the neck.

[mroliver77]

I would go with the as cast diameter and load as long as you can. This boolit shoots good in some of my guns and does not get close to the rifling. Stay with the gas check for now. Many here would be happy to send you some slugs to try.
Personally if the throat is bigger than the bore and the bore is relatively uniform, I try to fill the throat up to within .001 +/-. You did not mention what alloy your using as that can make a big difference.
J

[geargnasher]

With that info update, I'll have to go with what Mroliver said, I have plenty of experience shooting boolits .004-5" over groove diameter and you should be fine. The point is to get that boolit to fill the throat better for better accuracy, that's why I mentioned on the other thread that "generally" you should size based upon groove diameter, but if the boolit doesn't get a straight start it won't do extremely well downrange.

For now, see what you can do with what you have. Shoot a few boxes of your boolits gc'd with the Felix and Lithi-bee you made and then we'll see.

For really good accuracty, you will probably have to modify your dies to take up that huge bit of slack in the chamber area, or to load anything fatter than .312" without swaging down your booltis. I'll bet with standard Russian dies you're case neck is so tight it's squeezing the boolits down to .310" as it is when you seat them. but don't get carried away just yet, you should be able to group pretty well at shorter ranges with what you have. If it still leads, then we need to look at boolit diameter upon firing, and maybe get you a bigger expander stem.

Gear

[okksu]

Whooppppppee!!!!!!!!!!!!!! Went to the range today with friend and my son. Took a plethora of milsurps and burned some powder! Most execllent Boolit results, especially with the K-31, with the Lee .312155 sized to .310, GC'd amd lubed with either some Felix, some others with Fryxell's favorite. Both seemed to work about equally well.
On the Swiss it didn't seem to make hoot what lube, or what charge, 15, 15.5,16, or 17 of 2400, all would give me a 5 shot 2" to 2.5" group @ 100 which is as good as or better than I can do with the rifle with GP-11 or any j-hand load I've tried. Just a little elevation adjustment on the sights and they grouped right in there. No leading and a shiney, shiney barrel after 35-40 rounds! I've got to work on the Swiss's neck tension (probably my sizing/seating technique): about 6 out of 40 were too loose in the case, but the ones that didn't fall in were all very nice rounds down range.

The Finn M-39 was not quite as good, but NO leading after many rounds and gave consistent groupings at <5" at 100. Not great but for a blind ol fart, not bad, and there's reason for hope.

I'm still thinking the Finn needs a different boolit, but still I'm excited about the prospects going forward even using the .312155 in it. I've had j-loads that were much worse than 5" through that rifle. As noted, my first boolit outing was a disaster with TL and No GC's but this was totally different. TL may have its place but apparently it's not for these two rifles.

[geargnasher]

Feels better, doesn't it?

Your dies should, ideally, leave you with a couple thousandths loaded neck tension. That means .002" or so over your actual boolit size, so when you seat it, the case has to swell .001" in radius or .002" overall diameter. You shouldn't need any crimp, but sometimes it improves ignition consistency and therefore accuracy. Emphasis on sometimes.

As for the Finn, I would look for a Loverin mould or a .303 British boolit like Lee's pointy one, something in the .312" as-cast range, and 170+ grains. If the bore is good enough to not lead with the loads you've used, I'm sure you can dial in the accuracy with a boolit that fits the throat better.

If you could post some pics of your bore slugs it would help, and there are many others better than me to make a mould recommendation.

Gear