This screw is the most difficult of almost any to remove. If it does not have to come out, don't do it. I've had the slot misaligned on several guns, the worst looking thing on a Parker, and had no initial success on getting them. But could not stand the misaligned screw. Even sent one that had been case-colored in the frame to a very well respected smith and he could not get it out. But I finally did. Here is how.
Take the receiver to the work bench and turn over to the non-slotted side.
Fill the hole around the screw with a good penetrating oil, not WD40, and leave for a day.
Next day, repeat on the slotted side. Let it stand for a day.
Now if you have a pencil torch, heat the end of the frame gently, never getting it hot.
Wipe out all of the oil, and use acetone to remove all oil. Tape the receiver around the hole to prevent scratching.
If the screw slot is misaligned, mark the back side (non-slotted) with a sharpie, copying the incorrect angle of the screw slot on the other side.
Use the correct bit from Brownells. The best thing is you must have a complete set. The screw slot will be one of two sizes from experience, some are thinner slots than others.
Clamp the receiver into a padded vice (not cloth), screw slot up. Even better yet, still have someone else to hold it.
With the correct size bit, and a small ratchet on the bit with an extension handle (small pipe on the handle), the screw will come out. But you can break bits. It is a difficult process to apply downward pressure while turning the screw. Don't let it slip.
Once out drive out the back side of the roll pin through the hole, and I use a brass punch to prevent damage. Have the receiver on a padded (I use leather) wooden block while SOMEONE ELSE HOLDS THE RECEIVER/STOCK.
Now if misaligned, the threaded side of can be realigned based upon the mark that was placed on it before drifting out. Cheat a little towards not having to tighten it too far. It is a pain to have to do it over, and you will never see one back out from not being completely tight.
Now the slot will align, and if you have a loose barrel on the roll, a new roll may be inserted before reinstalling. But this is another story as it may tighten it up or make it looser with a new roll.
Not responsible for any accidents (dropped guns, broken bits, ruined screw heads) and written for entertainment purposes only.
p.s. I have been able to tighten up screws that were not aligned by using the correct bit with a ratchet, without removing anything. But this is where you can break a bit if it will not go into proper alignment. Then to align there is no choice but removal. One will see lots of guns where the smith has often placed the slotted side incorrectly on the right side. I could not stand that so I know what I would be doing to them.