I'm trying to recall a game I used to play on the Atari ST (520 I think). The game is either one or two player. The players play a gun in a half sphere shape moving forward down a half pipe. If you push forward on the joystick, a defensive shell appears over the gun and the 'ball' rolls on, protected. At least until you hit a mine, at which point the shell is blown off.
You can move or skid left and right, and possibly forward and backward. You can push your teammate to the far left or right up the side of the halfpipe killing them, destroying their gun.
I'd appreciate any help you can offer.