I have a post-ban, 20" Bushmaster barrel with a y-comp brake pinned on, I am wondering if it is threded underneath. If it is what is best way to remove it, and if not, will the threading process be afected by the brake being pinned in place. all replies will be appreciated

If you can see the pin sticking out, it is not threaded.  At least that is my understanding.  If you can see a little heat mark, then it is pinned and welded and there are threads underneath for your new no-ban muzzle device.

The best way to get it off?  If you can see the pin, find a way to tap it out.  If you can see the weld mark, use a grinder to go down until the pin will come out, don't get into the threads.

I am suprised that there haven't been more people respond to this.

Most Bushmaster 20 inch barrels with a muzzle device are slip/pinned on , no threads. You probably have a pin going horizontally on the lower part of your barrel, which would confirm this, no threads

A Y-comp on a 16" or longer barrel is just cross drilled and pinned.  The pin is the same one used as the FSB.

Bushmaster says they just put the barrel and Y-comp in a jig, drill it, put some red loctite on it and tap the pin in.