Let's talk TRANSONIC!

[Don McDowell]

You could get what maybe 3-4 grs. 10 grains at most more lead in that cavity? It's still a matter of length and diameter.
I have a couple of nose pour adjustable moulds, utilizing the "original postel" nose, with a cupped base, and yes you can still get a bullet long enough to not be dependable at distance in windy conditions.
Not all the bullets that the ODG's shot were hollow based, many were flat based. The equipment lists provided in Perry's book show that, as do those few remaining samples of bullets from Winchester, Gibbs and Metford. Nose shapes have changed little over the centuries.
Interesting find's when you read some of the old stuff, you have to pay pretty close attention and you'll find some real gold items. One example is in the 1875 Remington catalog , they say flat out that weighing each charge, and thorough cleaning between each shot, will help keep you from second class shooting. They go on to tell how the use of hardened alloy will improve long distance accuracy. Then they go on to some rather dry typical advertising stuff about how it's much easier to attain first class shooting by using their ammo, but if you want to reload your own they'll sell you the patched bullets, and if you really want to do it all on your own to cast the bullets from pure lead with a bit of tin added, "maybe 3/4 ounce per 16 oz of pure lead".
The letter from Bodine to Sharps reprinted in Seller's book is also another one of those ah haw moments.