me and a friend used Norma R1 to blow up a short barrel many years ago , it was more like a long thunder mug than a cannon 
bored out from a solid piece of steel 
bore diameter approximately 30 mm , outer diameter I guess was approximately 100-120 mm 
dont remember exact , it was a very long time ago 
we used a wood plug
ok guys dont try this at home  

  or should I say  "hold my beer"   

well it wasnt as dangerous as it sounds, we had it in a former military bunker when we set it off