I've slugged the bore but, being a 5 groove, I'm not sure what it tells me (measuring from a land to a groove.) I made a cast of the chamber but not an impact cast, do some shrinkage will have occurred. The throat measures approximately .311, not allowing for shrinkage of the cast, so probably at least .313?
Since I have three 30cal molds, I had hoped one might be casting at a big enough diameter to work in the No.4, at least as a short range load.
Unfortunately, the two molds for gas-checked bullets drop at .311, they are the pointed and flat nose (larg-ish meplat) designs shown below.
The 240gr bullet is .314 and looks to have a bore-ride section that might work, if I am interpreting my crude tests properly. Needless to say it would be quite a sedate load, presumably with a fair bit of bullet below the neck
240gr .314 bullet

Gently pushed to ensure rifling engraved a little

A Rifling marks just visible


Flat nose GC bullet:

Flat nose drops in:

Pointed GC 150gr

Drops in:

So, can the wise cast bullet-makers guide me? Can I use this 240gr plane-Base bullet or is it too heavy, long, narrow, etc.
Perhaps I should just wait for the Lyman 314299, which I have available in next few days.
Thanks in advance.