20.75 inch Civil War Bayonet > for 1861 Harper's Ferry .69 caliber musket?

Description

Antique
Socket
bayonet, used, but in excellent working condition:
the swivel moves easily, only very light rust marks.
I have thoroughly examined this and cannot find any arsenal markings on it anywhere.  It is both larger and longer than the .58 caliber bayonets I have had before and, to the best of my knowledge, having asked a lot of people at gunshows and done my online research...nothing definite, unfortunately...it is mostly likely a bayonet for the Harper's Ferry type .69 caliber, smooth-bore muskets used by some units at the beginning of the Civil War.  The lack of arsenal marks might mean 1) it's Confederate, or 2) it was an import.  Most likely, however, it was
3) made by a non-government blacksmith
for use with .69 caliber U.S. M1840 and M1842 muskets that were updated by rifling the barrels and, in the case of the flintlock M1840, converted to percussion ignition (text here and below borrowed from WORLDBAYONETS.COM) or it's possible it was the end of a production run as they were changing over to the .58 caliber rifles, so nobody bothered to stamp a US into the blade...or, maybe more likely, it was Confederate (both sides used .69 caliber rifled-muskets early in the war) as the Confederates didn't always bother to spend the time marking edged weapons.
Alternatively, it's possible (although unlikely) that this is a bayonet for use with the .45–70 caliber Winchester-Hotchkiss rifle or with the military musket variant of the Winchester M1876 and M1886 lever-action rifles (very few made)....
although the 45-70, at least in theory, should have a smaller-diameter than the .58 caliber (and this barrel-ring on this bayonet most definitely has a larger, inside socket diameter than a .58 caliber bayonet),
I'm sure someone out there knows what it is....please feel free to send me a message so I can update the listing.  Whatever it is, it's an interesting piece of history...and is probably much more rare than your typical .58 caliber bayonet!
Please allow at least 2 weeks for delivery.