I'm no gunsmith, but falling back on basic fab techniques ...
Using the removed screw as a guide, find a QUALITY drill bit slightly larger than the threaded portion.
Chuck it up into a variable speed drill (drill press would be best) and on a SLOW speed and using low pressure, slowly drill out the center of the stripped head. Don;t be afraid to use mass quantities of oil and lube to keep the heat down and the drill moving freely.
Drill through the button top being careful not to drill too much into the top rail. Use the removed screw as a depth gauge to estimate.
Once the button top releases, stop and you should be able to lift off the top rail.
You should have a small section of the threads revealed and very well could thread out by hand because with the button gone, the clamping force should be off the threads.
That's all assuming the threads aren't galled. If they are galled, it's time to order a new barrel and a proper gunsmith tool kit.
Good luck!
Using the removed screw as a guide, find a QUALITY drill bit slightly larger than the threaded portion.
Chuck it up into a variable speed drill (drill press would be best) and on a SLOW speed and using low pressure, slowly drill out the center of the stripped head. Don;t be afraid to use mass quantities of oil and lube to keep the heat down and the drill moving freely.
Drill through the button top being careful not to drill too much into the top rail. Use the removed screw as a depth gauge to estimate.
Once the button top releases, stop and you should be able to lift off the top rail.
You should have a small section of the threads revealed and very well could thread out by hand because with the button gone, the clamping force should be off the threads.
That's all assuming the threads aren't galled. If they are galled, it's time to order a new barrel and a proper gunsmith tool kit.
Good luck!