there ARE three round burst modules as i actually worked on one for some ( it was replaced tho as some1 got one in that was better and smaller than mine)
BUT i could use my last design and redesign it
AND mine was a TRUE three round burst module, one trigger pull = 3 rounds, no more , no less ( it had a nice little switch to detect wen the trigger was pulled so it would reset the mech when it was released :3 )
i can work on it just not for a few hours as im a bit busy atm