Marrakai-

You've seen some account of my 16b rifles. I run ~2-3/4drm in the heavier of the two, three in your little 12b could be so.
It's easy enough to find out!

Fish some lousy old hulls from under the seats of your rover, start with 2drm, card-wad-ball and a long piece of string.
See if she's still good to run!
Keep it up like so up to 3drm, you'll know soon enough if she'll wanna blow...

--Tinker