Identification please

[earni74]

HELLO EVERYONE, I HAVE HAD THESE 3 PICTURES SENT TO ME AND ASKED IF I KNEW WHAT IT WAS, IT HAS BEATEN ME, SO I AM CALLING ON YOU GUYS, THIS PIECE IS BRASS/BRONZE AND VERY HEAVY AND ABOUT 75mm IN DIAMETER.

 

[highlandotter]

a weight for a balance?

 

[waffenamt]

Has 30 pounds per square inch stamped on it?
I was thinking it may be a safety device for a cannon breech?
The owners uncle served in North Africa in the artillery.
Cheers
waffy