Intoodeep,
You're right, it a gunsmoke mortar. The load is 90 grains of FG which completely fills the sub-chamber. I lucked out on the camera shot. I use a digital camera which takes 7 frames in about 2 seconds. I usually start the sequence as the fuse fire disappears into the vent hole. However things happen fast, and most times I miss the "moment of truth" and just capture a lot of smoke after the initial fire ball.
Here are a couple more luck "shots". The mortar in the second picture actually flipped over under recoil, but I've since added about 6 lbs of lead to the carriage to see if that will calm things down.
Cat Whisper - hit the sand bunker......on the next hole....gotta back down on that charge just a wee bit.......