Big caliber shotgun ?

[lokvar]

I think you will find that this is the base of a flare case. I believe that 27mm is the standard size for a flare pistol.
D.

That,s the right and the only ! Dear Sdesic i suppose that you must be a young digger?

[sdesic]

Young digger I am under a year...
actually I am building metal detectors and testing on close by hill / ex fort / wood / park

Those two are my first flare casings ...

Regards
Sinisa

[Steve T]

The markings and font remind me of the launcher cartridges for the big 120mm Russian mortars. Are you anywhere near where the Russians may have been?

[sdesic]

Bosnia and Herzegovina ...
location has activity for 200+ years

Ottoman Empire
Austria-Hungary Empire
German / Croatian / Hungarian occupation WWII
Yugoslavian army after 1943/1944 - 1950
public park 50 years