I am trying various type of the throw away propane cylinders,small air cylinders,
88/90 gr pre filled cylinders that are used, and they come in various sizes.
I find them at the local dump for free,
make sure they are completely empty, remove or punch out the fill core,
the used a lag "Eye" bolt in the hole for hanging etc.
Section of grader blade cut off also work very well for AR and PB rifle,
along with old used up disc blades, from the local farmers etc.