It can be soaked in any good penetrating oil for several days, then placed in heated oil or in boiling hot water before attempting to unscrew it.
Try to bear down hard on the screw driver so that it can bite into the screw slot enough to be able to put some reverse torque on it.
Since they can be very stubborn it can take perseverance to get it out.
There's also trying an impact wrench, and as a last resort an easy out screw removal tool.
Less expensive impact wrenches are sold on eBay.
Some folks prefer to leave the screw stuck as it is but that does make it tougher to clean out the flash channel.
However it's possible to shoot out the blockage by placing a little bit of powder under the nipple after soaking until it loosens up. A CO2 ball discharger or compressed air may also work.
But shooting the blockage out can certainly work, especially if the blockage can be softened up first by soaking it. Then dry out the drum before putting in any powder.
You said that you can't see light through the flash channel, but is it possible for air to pass through the flash channel and out the barrel?
Last edited by arcticap; April 23, 2012 at 11:50 PM.