For the Wyoming shoot just fill out a 5320.20 at the link below and send two copies to the NFA branch of the ATF. Mine have been taking about 2 months for the ATF to process so send them early.
http://www.atf.gov/forms/download/atf-f-5320-20.pdf
Also from the Wyoming NFA website:
For those of you that need to fill out a 5320.20, the actual address is Garrett Ranch, 19415 South State Highway 487, Casper, WY 82604. (Natrona County)