I was in a play once where we were going to fire a blank onstage, in a fairly small black box theatre. There were two options, a .22 and a .45 caliber blank. The .22 made a sharp CRACK that really shocked you. The .45 made a VWOOM sound that filled up the entire room and left you with the feeling of a wave of violent energy having just passed through your entire body.

We went with the .22.