Trapdoor modification-

[JBinIll]

Interesting that's it appears to be made from an 1866-

34313

[Dick Hosmer]

And a once half-way decent one at that. Looks to have some sort of anti-burglar trip-wire setup. Are those not illegal in most jurisdictions?

[JBinIll]

When that was made I doubt it was worth $1.50 as a rifle and the NFA Act didn't exist.LOLI'm not sure about the regs covering those.There are factory made ones but they aren't made out of cut down long guns either.
That's a picture someone posted on a vintage sporting collectables page.

[musketshooter]

It appears to be a home made "game getter" set up. Hook was for attaching bait (meat).