I think i know how this works!
In the thin green strip in the bombs there's some oncollie that spawns a circle that grows larger and after some time delete's itself
Converted - My one uses some fancy oncollide in the red oval - and mie is more powerful that 1storange's (including that his one doesn't work in your gun )
Very,Very nice, I tried making a mechanical version of this which rotated a box above the walker to balance it rather than change the wieght of the boxes and it sorta worked, but onlyy with realy flat terrain