Download DMCannon.u HERE (Includes .u, .uc and example UT map)
 
DMCannon

This is identical to the TeamCannon included in UT except that it can be used within Deathmatch games, and it can also be triggered on and off etc.

If you set bRememberPlayer to true then the kills from the DMCannon will be allocated to the player who triggered the cannon. (I also think that if bRememberPlayer is set to true then the cannon projectile do not hurt that player. If you want this could be fixed so that the cannon didn't track that player!)