Help! Assistance with WWII Ammunition

My Father was a WWII veteran of the US Navy where he served aboard destroyers.
He has passed away recently and while going through his things, I found a box that I have never seen before. Inside were two shell casings and two shells. I will admit that I know next to nothing about ammunition. My main concerns are safety and legality and of course what exactly I have.
I have poked around some on the internet and a number of the postings etc. point to a resource on a web hosting company that is out of business. From what I’ve learned they are 20MM Anti-Aircraft rounds.

The casings have no gunpowder in them and I assume are perfectly safe and legal to own.
The are marked MK2. 20MM B.C. 1943 and they have symbol of some sort stamped on them but I can’t make it out. They look like this:

The shells have the same markings, although a different date. They are marked
MK3 54F 11/42 MAT & MK3 54F 11/43 MAT One is painted a dark green
and the other appears to be unpainted.

I would have put more pictures links up but it seems I am limited as a newbie, I have been keeping the shells wrapped in anti-static bags and stabilized in a sturdy metal box, in a metal cabinet away from the house.

Any advice? Thanks in advance.

Here are more links to pictures of the shells:

Can you show a side on picture of the cartridge case please. I think these are either 20mm Hispano or 20mm Oerlikon and a side on picture will confirm which it is (if it is).

I’m not familiar with what the US Navy used, so I cannot help with the colour or mark numbers. The green projectile could be innocuous but the brass top portion is a fuse. Whilst it may be a dummy fuse, I would treat it as live until someone with more knowledge can comment with more authority as to what you have there.

Be very careful not to drop it. I’d go so far as to not letting it bang around in the steel container that you have.

I think this may be a 20mm Mk 3 with a Mk 2 case. More details can be found here. The dark green color indicates a blind loaded and plugged round, but the unpainted one could be anything. I’d go with Mayhem’s comment…you may want to get these looked at by the pros.

Thank you for the replies and the link to the reference. I have them wrapped in a towel to stabilize
them inside the metal box so they won’t rattle around in there.

Here is a side view of the casing/cartridges:

I guess I was hoping some folks here would be like “Oh. Those? Perfectly fine. No worries”.
Seems like that will not be the case! I’ll have to figure out where to go from here.

20mm Oerlikon.

The projectiles may well turn out to be perfectly safe. It is just best to treat them as dangerous until they can be positively identified.

It is good to see safety first promoted by fellow collectors.
I would use a piece of inner tube rubber and using a vice screw it under 20mm and using hand pressure only with pressure on the base, try to unscrew the fuze anti-clockwise carefully. If too tight do not proceed. I find many inerted projectiles tend to sieze up a bit if left un-oiled for years and will undo using this method.
I hope this information is OK to print on this forum. I use it often. Ron.

I would like to thank everyone for the responses so far. It helps some. It would seem like the
green shell might be safe, while the unpainted one is a wildcard.

I will keep digging and see if I can come up with a reasonable plan.

All is well that ends well.

The fuse on both shells turned out to be just a cap that looks like it was made out of brass. No dangers there. The unpainted or “zinc” shell I think originally was the real deal. It is empty but there is a tiny amount of yellow powered residue on the interior walls. I’m guess it was Tetryl maybe? In any event, I’m guess Dad must have emptied it, and swapped out the fuse with an inert one for a souvenir.

The green shell was listed as blind loaded & plugged in the chart kindly posted above and it’s fuse is also just a cap. The shell is filled with what appears to be plaster of paris or something similar.

I feel a great deal better now. Thanks all!

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