Finally broke down and purchased a Bushy post-ban 16" and would like to install a muzzle brake.  I see Bushmaster sells post ban slip on brakes, but they are held on with a taper pin so a 1/8 hole must be drilled in the barrel. Is this a good idea or should I have the barrel threaded (at a later date in Sept)?  Will this pin method secure the brake efficiently or will it loosen in time? Thanks.  

There are also set screw retained brakes. I'd go with the threaded muzzle and a Wilson or Cav Comp. Forget the perm attachment BS in 3 weeks!!!

just wait

By the time you send if off UPS Ground to ADCO or KKF give them about a week to thread the barrel and replace the front sight, then another week to send it back, the ban will be over.  Hopefully.

wait three weeks and put a flash hider on it. A brake is superfluous on a 5.56mm weapon.