It depends on the mech really.
You really need a short lightish trigger pull to be able to get high BPS.
With most mechs, even if you could set the activation point really short, once it cycles etc it will have to travel back, a long way on most.
If you file down the sear, it will eventually wear away and become unreliable as well.
The best mechs were/are Automags, which, provided you used decent input pressure, could do 10 plus BPS without bouncing and with really high pressure on RT Mags, 18 to 20+ BPS bouncing. This was before the ULE triggers etc which make shooting a Mag fast, very easy.
Tippmans 98's etc about 6 bps, A5 despite its claim of fastest marker in the world, maybe 10 at a push.