I used to have an Ideal 456122 mould that had been special-ordered with an enlarged hollow-point to take a .22 blank in the hollow-point. (The obvious problem here is that if you drop a loaded cartridge, it falls point-down: landing on the blank. I never cared for that idea.) I experimented some with filling the nose cavity with olive oil, sealed in with a bit of wax.

First problem was that wax would soften (due to heat or some reaction with the oil, I never looked into it). Shellac made a better seal, but the bullets and loaded ammunition still required care in handling.

Second problem was metering a consistent amount of oil into the cavity. I finally used a small insulin syringe. This was a pain to do, but bullet weights were fairly consistent.

The third problem was that the super-dooper-delux-oil-filled-expanding-bullet seemed to expand no more than one with an open hollow-point. I tried several alloys ranging from 30-1 lead-tin, to wheelweights (as-cast and heat-treated as hard as I could get them), to Linotype. In no case was the expansion or splintering of the nose greater than what I got from the same alloy without filling the nose.

I also experimented with composite bullets: a nose of soft lead, with a base of harder lead. These were cast in one go, with the soft lead in one pot and the hard lead in another. From a rifle there was little difference, but sized down to .452" they did perform better than a mono-cast from the 5-shot 45 Colt Linebaugh I had then.

For my uses, the plain bullet worked as well as anything. Of course, a 45 is not an 8 bore, and I was not hunting tigers.