40mm shell casing - need identification please

[Mike Irwin]

Yep. That's a proximity fuse.

 

[SHR970]

Looks to be a 2" diameter at the widest.

Incorrect, by your photo it appears 2" wide at the base...not the widest place.

However, comparing your first picture vs. the first picture in my first link and your diameter of the base it would appear to belong to a 3" 50 caliber.

Edit to add: NavWeaps 3" /50 What they are listing as VT ammo means Variable Time. That was the name given to the fusing / round to hide the fact it was Radio Controlled Proximity.

 

[Casings]

I didn't get my measurement from the photograph. The lens is so close to the fuse end that the photo itself is out of perspective completely.

See the shadow on the ruler... its protruding to the lens. The ruler is positioned on the lip of the cone.