While full auto and other rates of fire like burst are allowed in rec play in the states, only semi auto is allowed in the tourneys. 1 pull = 1 shot. The skill is to be able to pull the trigger quick enough to achieve a high rate of fire. However some people have boards that when they reach a certain rate of trigger pulls per second start add extra shots E.g. 8 trigger-pulls per second = 15 shots per second.
This is sometimes known specifically as Rate of fire Ramping. and allows higher rates of fire to be achieved, but aside from being cheating, increases the likelyhood of someone getting hurt.
Another more dangerous type is dwell ramping. The dwell is the amount of time the valve is open for. The higher the dwell the faster the ball comes out of the barrel. The guys that use this are trying to get round the chrono judge by chrononing below 300 foot per second at the start of the game, and then playing at a higher fps.
The benifit of this is longer range, hits more likely to burst. The cost - a ball going straight through someones lense, over the top bruises etc, crushed widepipe.
The can be detected by chrono judges in most cases, but there are also cheater boards with concealed functions like tap-tappity-tap-tap a code on the trigger and then hold it down and you have full auto or higher dwell until another code is put in or there are no shots fired for a few seconds. This is so that when a ref trys to check the marker at the end of the game or when the player is eliminated, the cheat functions are deactivated.
The NXL (top US x-ball clique) have basically give a green light to cheater boards. Why? - to make the game more interesting, easier than dealing with the problem, who knows.
The NPPL have taken the opposite tac clamping down on it disqualifying teams found to be using them and banning use of kit manufactured by companies that produce cheater boards.
One recent controversy was that smart parts have released a marker (the nerve) that has ROF ramping as standard. Seems a bit silly as all the chrono judges now know this, but hey.
Not a conclusive answer but what i understand on the topic. Hope it helps.