The long-defunct "Riverbrand" company here in Oz made plain "lead" and jacketed soft-point bullets for these.

I don't have any of the "lead" ones here at the moment, but I do have two 100-round packets of the jacketed jobs.

The packet says, (VERY faintly): "100gn", which is about right and they measure out at 0.3155" - 0.3160" (ish) with the bulk being clustered towards 0.3155".

Not made since about the late 1960s, it seems.

If I had a Cadet in .310, I wouldn't be firing these; preferring to stick with "proper" bullets.

A couple of companies here have made heeled bullets for the .310, including one that finished them in a black, "polymer" coating.