Correct, the ball detent is called a "ball latch" in tippmans. The latch is orange rubber and is located in the chamber of the marker where the cyclone feeds the balls in. Whit the front of the marker pointed this way <--- the latch should look like this _\__ if it is looking like this __/__ its in backwards.

Once the head of the stripped screw/bolt is drilled off, then the recivers (marker halfs) can be seperated and there will be enough of a stub left that you chould be able to grab it with a pair of pliers and turn it out.