Lee has just started selling what it calls the "Universal Case Expanding Die". It's really an adjustable belling tool to flare the case mouth a bit so you can seat cast bullets without shaving. You can do the same job by forcing any handy tapered round object into the case mouth but the Lee gadget should be a little easier to use and more uniform.
You did not say if your bullets are gaschecked. If they are, 20 grains of either XMP-5744 or 4198 is a good place to start. If they are not, try 7.0 grains of Unique.
Now would be a good time to slug your Type 99. They vary considerably in bore size and, if you need something odd to make it work, you have your .30-30 project to play with while you are waiting. Check to see if the bore is chrome plated. The earlier ones are and are much better quality overall. If your's ain't, you might wanna get it thoroughly checked before shooting it.
Lee offers a pretty good range of sizing dies and will make you a custom size for $25. With any luck at all, one mould and two sizers will feed both the .30-30 and the 7.7. You're pretty much gonna have to cast to feed the 7.7 unless you are really lucky in the bore size.
Cases formed from -06 or 8mm are likely to be a bit small in the base for the chamber of the 7.7. (Again, considerable variation exists.) I would be hesitant to use such cases for full power loads, but they work fine for moderate cast bullet loads. One tip is to put a wrap of tape around the base of the case before fireforming. This holds the case centered in an oversized chamber so case expansion is uniform rather than bulged on one side.
