when you reach a certain bps the gun automaticly jumps upto the wanted bps.
like, millenium ramping:
you reach a consistant 6bps (balls per second) and once you hit the 6bps the gun automaticly jumps upto 12bps.
basically its a assisted shooting mode, unlike Semi were its one pull one shot. In ramping once you've hit a certain Balls per second, you get multiple shots for every trigger pull.
as james said semi no mater how fast you shoot it will shoot one ball for every tirgger pull.
but if you set your gun to millenium ramping once you hit 6bps the gun will jump upto 12bps.
and as for legal restrictions on ramping,
most torurnaments are capped at 12bps like masters and PA.
masters 5 man and PA are mill ramp 6bos kick in and ramp uto 12bps..................... PA 5 man which is still semi capped at 12bps.