Originally Posted by
Heavy Metal
Remember, you are trying to break the corners on the bottom two cut-outs on the star-shaped hole in the extension, not the ramp itself but the clearace cut for the two lugs at the top edge of the feed ramps. It will have to be considerably thinner than a bolt lug to work. You are trying to give it an angle. A Jewelers file is very thin and flexes a bit. It is ideal for this. You can even get diamond dust Jewelers files that work work even better. Harbor Frieght sells both.
The cut out is shaped like a boxy 'U'. I try and break the edges on all three sides.
As to any debris, I would hose it with brake-cleaner and flush it out the muzzle and throughly re-lube.