7.7 Jap loading problem

[ChuLai 68]

I have two Jap 7.7 rifles. One has a .315 groove diameter and the other a .317.
I am new to casting bullets, but i have heard you should size them .001 to .002 larger then their groove diameter. I was able to find a Lee bullet mold in .324, but both Lyman and Lee sizing dies jump from .314 to .321.
Lee will make a custom sizer die for $30.00....i'm thinking i need a .317 as a compromise to use for both rifles. Am i right in my thinking here?
Also, how far down can you resize? Say from a .324 bullet, how much smaller can you make it?
One more question. Are these two bores shot out? I mean i can see nice rifling, but since Jap military bullets were .311, wouldn't it follow that the groove diameters wouldn't be .315 or .317?
Thanks!
Rick

[38-55]

Hey Rick,
What is the measurement of the lands ? I've had good luck with sizing stuff for the 7.7 at .312. They tend to have very deep grooves and very large ( tall) lands...
Calvin

[ChuLai 68]

I will have to get the slug and re-measure for the lands....i thought the choice of bullet diameter depends on the groove diameter? No?

[hydraulic]

I have two '99s, an early and a late war. Both have bores that vary from .302 to .315, depending on what part of the barrel is being measured. The slugs, 00 Buckshot, come out lop sided or oblong, like one side of the barrel has been flattened.. Even with all this, they shoot well with 311413 bullets sized .311, 13 grs. Unique.

[Bent Ramrod]

ChuLai,

Lyman/Ideal used to make a 316475 boolit mold for oversize Japanese and .303 British rifles; you might look in the catalogs of the custom mold makers to see if anybody reproduces something like this.

Yes, the rule of thumb is that boolits should be sized to a little over groove diameter. This is a good first approach, but every rifle is a law unto itself. My own Japanese rifle has a couple tight places of maybe .314" and no telling how wide the intervening spaces are. I found an oversize Ideal 308291 with a shank I can size to .313" and a nose that I lapped out to .303" that shoots 3-1/2" or so at 100 yards. It's right on at the 400 yard sight setting.

With a good press and enough determination, you can size soft lead slugs down quite a bit, without too much distortion, as long as the grooves are well-filled with lube first. Going from .324" to .317" should be doable, as long as you use a heavy sizer or a sizer die for a loading press, like Lee offers.

If I was you, though, I'd get the .314" die and look for a Lyman Lyman 314299 mold. This design has a long nose for guidance and a lot of inertia for slugging up. If you Beagle the cavity oversize from this, you can try them unsized; if they work un-Beagled or sized down, you're still doing well.

[chevyiron420]

rick, you also have to make sure your rifles chamber can freely except a case with a bullet that big seated in it. if the chamber is tight on the case neck BAD things can happen. im not up on jap rifles, maybe they have big chambers, i dont know, but better safe than sorry.-phil[smilie=2:

[ChuLai 68]

Thanks for all the help Gents, although i have been reloading for 40 years now, this is my first experience with making my own boolits. Its safety first with me, so i appreciate all the great input i'm getting here....and i certainly will check how easily they chamber, as Phil suggests. I did buy a Chrono to help me work up loads.
I do have several hundred FMJ boolits that were pulled from 7.62X54 cases.They are all .311 diameter.....does the same apply to FMJ bullets, i mean as far as trying to get a boolit diameter just over the groove diameter?
And is the reason a .311 boolit will shoot well in a rifle with a groove diameter of .315, because the "lands" actually do contact the boolit?
Thanks again Guys!
Rick

[Phil]

If you're using Norma brass (that is the only factory brass I have used) you can get away with bullets as large as .316", at least with the four rifles I'm currently working with. If you are using 30-06 brass you will have to turn the necks if using .316" bullets. Again, this is with the four rifles that I'm currently working with. Seat a bullet of the diameter you intend to use and measure the neck diameter of the cartridge. Then make a slug of the neck of the chamber and measure that. If the cartridge neck is at least .002" smaller than the neck of the chamber you are all set.

On shooting undersized jacketed bullets, yes they grab the lands and may or may not shoot well. But the chance of flame cutting the barrel due to the grossly undersized bullet is always a possibility. If it is a chrome lined barrel it will probably delay flame cutting but not forever. I haven't shot a jacketed bullet in a 7.7 since the sixties. Guess I'm just a cast bullet junkie!

I've Beagled a 314299 mold to .316" on the body and .306" on the nose and with a Winchester Large Pistol primer and 13 grains of Red Dot they will regularly shoot in 3" for ten shots at 100 yards. This is as good as I can do with a bead front sight. Gonna put a Lyman 17A with an aperture insert on the front and see what happens.

Cheers and good luck,

Phil

[TAWILDCATT]

try what you have first.then if its bad try the other ideas.if you made a hand die you could bump the bullet up.the old C & H swage presses would be ideal for that.
:Fire: :coffee:

[fourarmed]

It's an easy matter to hone out a sizer a few thou. Just split a piece of steel or brass rod a couple of inches with a hack saw, chuck it in a drill, and wind up strips of 400 grit emery cloth so that they fit snugly in the sizer. I use a piece of 1/4" rod, and strips about 3" long. Turn on the drill (a press works best, but a hand drill can be clamped in a vise) and work the die up and down on the emery cloth. When the cloth quits cutting, clean up the die and drive a slug through it. If it's still too small, use some fresh cloth.

[38-55]

ChuLai 68,
What tawildcatt siad !!! Just rember that when the 'big light' hits that boolit in the rear it WILL slug up ( and down) to your bore. Just make sure that it chambers ( and unchambers) freely. If the .311 or the .312 stuff doesn't work you could always get the lyman 314299... I have not seen a jap rifle that won't shoot that bullet.. but your mileage may vary..
Let us know how it goes..
Calvin

[TCLouis]

My sporterized Type 99 has such a good barrel I use .308 bullets and plan on .310 for my boolits out of this gun.
.310 boolits cause that is what I size them all for all of the 30 cals.