The tread in linacs and such is also meant for longlivety. The normal thread used on bolts is not ment for continious movement. It will wear down very fast(in weeks, not years).

The trade-off is in shape and TPI/pitch. But for use in robots this isn't an issue. What is an issue is the wished for power in the weapon.

Simply put, torque of an electric motor on the wished for power consumption. So do you wish a slowly turning amp drawing heating up motor near stall torque. Or a briskly running motor with a lot less torque, but better efficiency, starting at the motor.
I'm going to use the example of the Speed 900 motor. This has following specs on 12V. 13A peak efficiency- meaning 6600 rpm and 118 watt- what gives us about 110Ncm.
Stall torque and power consumption is 1.1Nm and 55A.

I'd rather gear down enough to get the job done with .11Nm with this motor, than to rely on the build quality of motor, controller/relay and batteries to get the 55A trough.

The gearing down can be done with several stages, like in a normal linac- first a worm gear and then a reasonably large trapezium or square tread. Combined with a motor of low RPM (aim is 3000 rpm- industrial standard)but good torque.

But for cheapness, I would use a normal thread (not fine)of M16 (is capable to take 12 tons), with a pitch of 2 mm. So every turn the nut moves 2mm. With only 0.11Nm you won't do much.
But using a first gear down from 6600 rmp to 150 rpm you have about 5Nm. (wiper motor gearing, hint) so, in a minute you have a travel of 3 meters with 5 Nm. If you would use an M6 with a pitch of 1mm, you would only do 1500mm, but with 10Nm.

A fun idea is to use a drill motor and gearbox, with a normal threaded rod with a fine tread.