I can't actually seem to figure out how to play unfortunately.. I'm not sure if it's a bug or not, but the bullets don't appear to be hitting the tanks. I had it happen maybe twice and I even destroyed 1 tank somehow. I couldn't figure out why though.
If you're having an issue with the physics system and the bullet going to fast, I would suggest using the Mario physics check method. Essentially, before you move, you calculate your next frame position, then check between the positions two positions to see if something will be hit. In unity, this can be done with the SphereCast or BoxCast