Just adding a small point to Daryl's excellent advice:
sometimes 1F in plastic hulls may produce small brimstone lava-prills that melt holes through the sidewall of the hull.
...possibly due to less efficient or incomplete burn?

My experimenting with BP in plastic hulls is vastly inferior to Daryl's extensive knowledge,
so I could quite well be doing something wrong (or stupid!)
but my recommendation would be to stick with 2F for plastic cases.