Barrels mist have a permanently attached muzzle device. Basically a blind hole thru the device and into the barrel, a pin pressed in then filled with weld. Must be a minimum of 16" including the device.
The bolt catch can be used exactly the same as without the BAD lever. It allows you to release the bolt and lock it back with your trigger finger as well as retain all standard function. It simply clamps onto the stock catch.
This bullet button shit sucks though.