Well . . . me thunk it would be a Conn rifle?  Why?
No French cross on the butt stock just behind the action.
No 'V' with crown on top of action front.
Centerfire.
Long trough breech block.
Narrow firing pin n' hammer nose.
No NYNC butt stock stamping(s), only what appears to the number 11. Only other stock stamps is the WC on left wrist.
Not a rimfire.
uh, I wanted it to be!!!!   

Other than the above, not sure what it originally was? With the lack of markings mentioned, wasn't thinking it was an overseas shipped rifle?  Could be I 'spose.  Always willing to learn n' welcome any input, k'.  .   

jhm - pm'ing you 'bout stock doings.

Here's a better/clearer view of the 'half rifle' action, along with a few others and a centerfire breech block that picked up 'bout 10 years ago - well of course on eBay!

Butt stock is an old takeoff from a NYNC iron.....and nope, not trying to rework that doorknob into a pretty butt plate!

Here's a picture of a few rounds, to show the .45-50 Peabody compared to a few others:
.38-55
.40-70 SS (2.5" .405 Win Hornady brass)
.40-90 SS Betram brass
.45-50 Peabody (reformed .348 brass, thickened rim)
.56-50 Starline brass case
.50-70 Starline brass