[Mike Irwin]

Most single-shot handguns of the time were smoothbore.

Henry Deringer's guns were not, they were rifled. That much can plainly be seen from the multitude of pictures available on the web of the Deringer recovered from the stage immediately after Booth shot Lincoln.

The most other commonly available type of rifled, single shot, muzzleloading handguns of the time were dueling pistols, and they were commonly loaded with patched balls.

The Model 1842 was a smoothbore - it's not analogous. It was also generally loaded from arsenal prepared cartridges in which the cartridge container was used as wadding to retain the ball in the barrel.

"The guns were normally sold with a bullet mould made to match the caliber of the gun"

Check the FBI write up available on the web.

The gun that was recovered from Ford's theater was .44 caliber.

The ball that was recovered from Lincoln's skull during the subsequent autopsy was of a diameter and weight consistent with a ball of .41 caliber.


And, saying that the bullet mold was made to "match" the caliber is a tricky thing, because in that time frame "match" was a highly variable quantity.

I've had the pleasure of examining two cased sets of Henry Deringer handguns over the years, both in the collections of the Pa. State Museum and Historical Commission. In both cases, the molds dropped a ball that undersized for the bore of the guns, undersized to the point where I suspect that the bullet simply would, as I described, have dropped out had it been loaded without a patch.


BUT....

It is possible that some sort of overwad was used to keep the ball on the powder.

But... given the distance at which Booth reportedly fired, a foot or less, one would think that any overwad would have been driven into the skull by the bullet and then recovered during autopsy.