I use rapid fire every day in COD5 waw if using the 555 it must be adjusted to slow it down with a pot use my tut in this section. if you are using a programed chip. it should be 8 pulses per sec or in hex 0x3F. works fine, not as fast as cod4 but still fast. you can fire faster than this, but you might get limited. you can fire in short bursts my mode 2 is 10 shots per sec, but if not carefull this may get you banned.
this has all been discussed before try seaching