I just watched Big Daddy Hoffman (and his son) fire a two barrel American Derringer Corp. derringer (M4 Alaskan) chambered for .410" shotgun - and the second barrel in the somewhat larger .45"-70 round ..
The .45-70 when so fired does seem to smack straight-back into the palm of their hand rather than rotate up and rearwards to imprint on the forehead.
There doesn't seem to be anything much useful to say.
Engraved Version M4 - That's Pretty.
Perhaps it may be worth adding that this M4 Alaskan actually has a 4.1 inch barrel - the .45-70 loaded cartridge is just over 2.5" long.