Interesting old guns. I remember a friend owning one when I was growing up. Pretty sure it is an Iver Johnson, although they may have offered it for sale under other "store brand" names, as Steve said, above. Looks like the original patent on the action may have been assigned to O. F. Mossberg. Here are a few links to similar guns:
Iver Johnson Single Shot 12 ga Shotgun Used
TO MARY - Google Patents
Shotgun ID help
Ring Release Iver Johnson Iver Johnson Shotguns for sale, gun classifieds or gun auction from TWIN OAK ARMS. Buy or bid on this Ring Release Iver Johnson in the category Iver Johnson Shotguns on GunsAmerica.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)