If you are doing multiple targets or have a club/range, it is recommended to pick up a chain disk to be used with an angle grinder. This attachment make shaping and removing a breeze.
Start with mixing container on scale and calibrated to 0.
Grapefruit/Softball Sized = add 150 to 250 grams of Part B
Cantelope Sized = add 250 to 450 grams of Part B
Watermelon Sized+ = add 450 to 850 grams of Part B
Equation: Part B x 1.45 = Total
Add Part A to mixture on scale to reach total. Stir. Pour.
We prefer to use a close quarter electric drill with the mentioned Scotch-Brite Abrasive Pad because it is much faster, however, we have had reports from some customers that they have used an orbital sander with 40-60 grit paper to shape/finish the repaired area.