Sail32, a small impact driver that takes 3/8" bits along with a proper fitting screwdriver tip can help a lot, but those small impact drivers are a little hard to find. There is a topic somewhere on this site, possibly on this '73 board or on the Colt Clone board, where somebody gave a link where those can be found. I have one I got from Harbor Freight some years ago, but they didn't carry it any more last time I looked, just larger ones.
I have also had good luck using a proper fitting screwdriver held against the screw head with the gun on a solid surface, and wacking the handle of the screwdriver really good with a hammer. Then leaning into the screwdriver while turning. YMMV, of course. Good luck