Mr. John,Thanks for the response. I did mean 40 grains (just enough to go bang). 1/2" gas pipe would be mild steel pipe used fo natural gas lines. I've built the carriage assembly with wheels and am having difficulty finding suitable barells. The breach end would be sealed with the loading gate. All I want to do is fire a rew blanks at a re-enactment for the spectaters who have never seen such a weapon.
Many Thanks,
Charles