What Gun Does This Ammo Go With?

[CapnMac]

As above probably a 2x or 3x teaching example, which may or may not have been matched to a 2x or 3x cut-away demonstrator.

 

[Pat Riot]

Are you planning to sell them? I would be interested.

 

[jrmiddleton425]

That is almost exactly the caliber and length of a loaded 1.1"/75 anti-aircraft round. They were fired out of what might be better known to you as a "Chicago piano." Produced 1938-42.