Fella on another site is inquiring about this oddity and it occurs that you might, by very small chance, know something about it's origins.
.25 caliber bullet gun with FM and round barrel. Twist looks to be about 1:18.
The owner's text description:
1) .25 caliber ML
2) It has an unmarked bull barrel.
3) The lock has the name of a London maker, circa 1870's "Wm. Moore & Co."
4) Single set trigger
5) On the left side is an engraved target and the words 'In Memoriam John Buhmiller"
http://wyomingschuetzenunion.com/ubbthreads.php/forums/22/1/General_DiscussionBuhmiller was known for large bores and Africa more than anything, but I've heard he dabbled with ML guns on occasion.
Couple of articles here on the 'Fire by Ken Howell about him, but otherwise I know nothing...