I've had this extra backplate / grip laying around for quite a while and I was finally going to clean it up but I cannot seem to get the buffer tube screw out. I've tried many things and I've even managed to bend the screw bit on my impact screwdriver trying to get it to move. Any suggestions how I can get this thing apart?
Been there and done, that as it were. More than likely what you've got is the "Spring Loaded Detent Pin" that locks into the grooves in the buffer plug has rusted in the locked position. There will be so much rust formed in and around the little spring under the pin that it cannot move down to let the plug turn. If you have the patience to fiddle with it: Clamp the backplate in a vise so the buffer points straight up, and heat around the plug area, not too hot or your fiber discs will die, and flood the thread with WD-40 or better yet Kroil or Screw Loose penetrating oil. Use your Impact driver to "Shock the plug alternately in both directions" Keep repeating this drill until the plug will move just a little. Reposition the bakplate in the vise with the buffer angled up a little from the horizontal, repeat the heating, oiling, shocking and use the little plastic tube to squirt the oil into the bottom groove "6 O-clock" in the plug. this is a straight shot to get the juice into the detent plunger hole. From here it's just a matter of "Luck" but most will finally work loose and come apart. The "Fail Safe" option is to make a Spade Backplate out of it. Cutting the pistol grip off allows you to dig whats left of the pin out of the buffer tube housing and let the plug turn. You can always trade it for a good pistol grip unit, to someone that wants a set of spades.
The short formula would be: A little heat, Lots of Patience, PLENTY of oil, and more cussing than you ever heard!!!!!!