I'm just reposting my project here:

Converting AR upper to "bolt" action.
04-12-2016, 08:50 AM
Stay tuned for the somewhat exciting process of converting an upper to bolt action!
See the thrilling saga of removing the muzzle brake, tapping and sealing the gas port!
Watch me struggle trying to figure out how to get around using the idiotic charging handle without slicing and dicing the upper (or my hands)!

But seriously, I have a Bushmaster 20 inch HBAR 1:9 upper that I picked up cheap from LI Ammo.
The brake looks like it was pinned but not welded (looks like a roll pin epoxied into the hole), and it's a nice brake so I want to save it.
The next thing to go will be the gas block. I need the space it occupies. The tricky part is closing the gas port.
It looks like I'll be drilling and tapping the hole with a 6-32 tap and screwing in a set screw....unless someone has a better idea.

So far I've ordered some parts to convert the handguard to a "pump action".

I've decided to fill the gas port with a brass pin that will be covered with a copper band and soldered into place. Easy on, easy off.
So far the only part being "butchered" is the handguard, and that's no biggie to replace.
Pictures to come.