Mold Suggestions for 7.7 Jap?

[Hanzy4200]

I would like to hear your suggestions on a .312 bullet mold. For now it will be for the 7.7 Arisaka but likely will get use in .303 Brit at some point. Also, sizing. I read some say .311, others .312, and .313. What's your take?

[Outpost75]

Best is to do a pound cast, measure it and order a mold to fit. Do not guess! #314299 or clones from NOE are good choice.

[Larry Gibson]

What Outpost75 said. I know some 7.7s run large and the NOE 316299 is the bullet of choice.

[Harter66]

I have Dad's to work up it's .318 . I'm just going to start with an 8mm bullet if Paper Patch doesn't work out on the 312-155 .

[iron brigade]

Yep noe 316299 is what I shot in mine. Type 99 rifles like big boolits just like 303 Enfield's.

[Hanzy4200]

Yep noe 316299 is what I shot in mine. Type 99 rifles like big boolits just like 303 Enfield's.

Next question. What gas checks do you use? I'm pretty new to GC's. I've only checked a few 30-30 bullets. I assume a .30 cal check wouldn't fit the shank of a .316 bullet?

[iron brigade]

Yes 30 caliber gas check is correct

[paul edward]

In my Type 99 Arisaka, I got poor accuracy using some .311 diameter gas check bullets cast in a Lyman 311299 mold.
These same bullets (and load) worked well in a 303 No 1 MkIII* and an 1891 7.65 Argentine Mauser.
Did not try any larger diameters as my old single cavity mold dates back to 1963 and drops at .311.

You will definitely want to slug the bore of your rifle to determine the appropriate diameter mold to order.

[Bigslug]

Best is to do a pound cast, measure it and order a mold to fit. Do not guess! #314299 or clones from NOE are good choice.

THIS!, and not only this, knowing the inside diameter of the mouth of one of your fired cases can be helpful too.

The .303 Brit barrel dimensions are all over the map. A lot of that is due to the fact the cartridge spanned the era of figuring out smokeless powder and copper jackets, and the 7.7, being a later construct, might have less of that to worry about. All the same, wear or shoddy wartime production can lead to variability.

You need to be aware that the NOE versions of the 311, 314, and 316299 blueprint for .300", .303", and .305" diameter nose sections, respectively. This can have a bearing in whether or not they'll even chamber in your rifle. I don't regret owning all three.

Pin gauges for the bore and case mouth, pounded slugs for the groove diameter, and a pound cast for the chamber are your tools for solving the Mystery of the Mil Surp.