Ww2 vet bringback Need help identifying casing and slug

Thanks for the Forum.
I found this shell in an old vets belongings. The cap is gone and shell is empty.
From what Ive researched it looks to from a Navy AA Oerlikon 20 mm.
shell reads 20 mm MK 3 M.D.C. 1943 A.L.
The shot is the question. I can not find this shape anywhere. I assuming it is all solid aluminum possibly a tracer or dummy?
Any help would be appreciated.

looks like someone turned it into a marlin spike/ fid. probably a bosun on some ship with some down time.