https://forums.gunboards.com/showthread.php?89347-W-M-morse-and-Company

A breechloader with the same marks
http://www.gundersonmilitaria.com/shotgunpercmorse.html

A sidelever; 4th one down.
https://www.rockislandauction.com/detail/2024/619/five-shotguns

No hits here, but several on George W. Morse
https://archive.org/details/gunmaker00satt

So we have ML, to sidelever, to toplever breechloader. If Morse was a maker one would think there would be more evidence thereof. I'm betting a tradename, maybe the Morse Hardware in KY?
The Missouri Hause came from KY. Hawesville in on the Ohio river.