As a machinist, I've removed a lot of stuck/stripped/broken bolts and screws. I strongly suggest NOT using most of the advice in this thread, especially drilling out the bolt, unless you have a mill and the skill to use it. But you wouldn't be asking here if you did.
#1 thing will be to get some heat to that to break the loctite bond. Then I would try the following options:
- Drive the next size up hex (not Torx) bit into the screw socket. The idea there is to make the hex bit re-form some of the steel in that Torx hole, so it's a tight fit on the hex bit. Doing the same trick the opposite way (driving a Torx into a stripped hex hole) works as well if you encounter stripped hex head screws.
- Do the Dremel/flathead screwdriver trick you originally mentioned.
- If you have access to a MIG or TIG welder, weld a nut to that stripped screw head, and unscrew it when it cools from red to gray but is still hot. The welding is done inside the nut, not on the outside.
I don't like the screw extractor method for something like this; it might work but you've got a good chance of breaking it off in the hole and making the situation worse. Attempting to drill the screw out without proper tools will most likely end up with your drill walking into the aluminum and messing up the handguard.
If you're not confident in doing one of the three methods above, keep in mind it'll be cheaper to take it to a real machinist than it will be to buy another handguard if you mess it up. My 2 cents...