Maybe an English Pattern 1839 bayonet. With no lock ring it's an earlier 1800s model. At first glance I thought it was a M1816 Springfield but the blade looks more like the English style. I'm sure one of the experts will be along before long to tell us for sure.
Yes pre civil war & British is as far as I've gotten. The 4" socket looks like it's made for a Brown Bess musket, but nothing else matches. Still researching. Maybe a colonial blacksmith copy of a Brown Bess.
Looks like a Brown Bess with land pattern shoulders.
I.D. of the socket at the bridge is 23mm. The total length is only 533mm, so not exact match. Left side of bottom of blade is damaged/missing/repaired, as it's not symmetrical.