jesse,

you probaby already know this, but i'll say it anyway cause i have no idea what else your problem could be...

dynamic mics are capable of handling LOTS of loud noise. this means it also takes a lot of sound to get a dynamic mic to register much level at all. so unless you have your amp turned up real loud, your sm 57 (or whatever dynamic mic you're using) simply may be incapable of picking up the sort of volume you're hoping for. on the other hand, condenser mics pick up every little thing.