My experience :
forget trail boss. My velocities were all over the map.
soon as the accuracy / velocities settled down, it was cracking. You can have the rest of the jug to try it out yourself.
7.5gr titegroup under a 190smk or equivalent, mag length.
a cast bullet will be 25-50 fps faster +/-.
your 1/12 bbl is less than ideal, but may work.
hard to say if it will tumble or not.
test 5-10 shots close to the muzzle on cardboard.
Joe, no need to buy any bullets for this.
I can get you going. I stacked them deep when
they were cheap.
I will be at Sir Walter Saturday, or can get them to you
via tweedle dee or tweedle dumb at zsa if it's not a snow pocolypse.