Frank, what you say makes sense. I have no way to determine exact shape of the nose to see where the radii and all are, but the nose on the Ideal looks a little fatter and is .314 just above the first goove. From that point the bands are as sized. The grooves are +/- .287.
The Clerke is a bit more pointy, starting at .319 and tapering upward, first band (lower) is .322. Groove is .296 and narrow. That may explain why the skinny shaped nose is still almost the same weight?
Overall length is within a thou. Both use a kiss on the rifling that equates to the same die setting being suitable, and I may add, easier to load

I was confounded by this at first since the noses looked a scosh different to my eye. It seems that the Ideal seats on the leade inside the lube groove, while the Clerke seats just ahead of the first groove. Barrel dimensions are .315 and .321 as best I can measure. Unmodified Winchester barrel from 1889, and just about perfect.
The Ideal has occasionally shot groups that are about 3/4, and tend to be an inch or a little above. Me, more than it being the limiting cause. The Clerke has never yet gone down to an inch. Limited number of trials. Mostly just over an inch and a quarter.
This isn't the end of the world, or a major worry. I would like to learn how to select molds with some higher likelyhood of success than just a wing and a prayer, though. Thanks for taking an interest here. Pat