Just came back from the garage.
Setup:
9mm ID 16mm OD steel pipe;
one end is reamed for a bolt;
bolt is screwed in;
at the end of the bolt there is a 1.5mm hole;
pipe is fixed in a vice, pointed at 6cm thick wood planks (in total), behind planks there is a tree stump;
0.75 +- 0.1 grams of nitrocellulose gunpowder from chinese nailgun blanks;
wad cut from a light wooden stick in duct tape;
8.14 grams crudely cast lead bullet;
Process:
Heat a steel wire, put it in the hole for reliable ignition;
SUDDENLY, the bolt BURSTS backwards, flies 20 meters, ricochets off stone pavement and leaves a huge dent in the wall
If I stood in the back of the pipe I'd be dead
Basically, too much gunpowder. Should have went with canonical 9x19 loading of 0.5 grams
Results:
9 cm penetration (6 cm wooden planks + 3 cm stump)
9x19 luger penetrates 6.85cm
WIN!