Deadeye; A heeled bullet is what you will find stuck in the neck of a .22 shell.
The outside diameter of the bullet is roughly the same diameter as the outside of the case. There is a "heel" of lesser diameter to fit INSIDE the case. This was done originally from two points of view.
1. The .44 Henry could very well be an extrapolation of the .22short, by doubling each dimension without other changes.
2. In converting Cap & Ball revolvers, there wasn't much meat on the cylinders for a larger case. The answer was, to back up the bullet of a size to fit the bore with the narrowest possible case. This avoided having to make new cylinders or open up the frame for the larger cylinder.
It was obvious, even then, that a bullet worked best when fitted to the inside of the case neck and was of proper diameter its full length. Very few rifles were made for heeled ammo, and other famous pistol rounds, like the .450 Adams, were already in sevice elsewhere, with inside lubed bullets. I think the historians give too much credit to the Russians.