That is the rear end of the barrel where the shell is inserted.
Near the breech.
Autos and pumps, on the receiver. Over/Unders are undr the breech locking lever
Where the shell is loaded.
From the breech.
From the breech
In front of the butt stock .
Less than $100.
Serial no. C8172
The Darne sliding breech shotgun comes to mind.
I'll take it for free :)
minimal length of a shotgun is set by the Federal Firearms Act....The barrell can be no shorter than 18 inches(measured with the breech or bolt closed, breech or bolt fase to muzzle) with a minimum overall length of 27 inches.
Need more details.