It should just slide an inch or so at that elevation (on grass). Wood bases slide a little less than channel iron.
You may want to stake it down when you get to the point of wanting to put two concrete filled beer cans through the hole.
My 4.5" (wood base, 103 lbs + base) will slide two feet on grass when down at 15-20 degrees above horizontal.
It's fun to shoot one at high angle (45-75 degrees) and then time the ignition of the next so shooting at low angle (under 45 degrees) the two bullets hit the same point at the same time. Tough to do when lighting fuses.
