Dean1818
Removing the rear sight is by far the hardest part of working on the M&P's. The sight is machine pressed in, at the factory. You have to first loosen the set screw. You will not damage the plastic spring cap, on the blocker spring under the sight, unless you use excessively high heat on the sight. The set screws are red loctited in at the factory and this means they usually need to be heated to get them to loosen. If you turn the slide upside down, as you heat the screw, the heat rises and this will allow less heat needed to loosen the set screw. Use a propane torch and set the point of the flame on the set screw for 3-4 seconds. It should loosen. If not apply a little more heat.
Before you remove the sight, note the location of the sight, left to right. This is for accuracy and you want to reinstall it to that same spot. You need to clamp the slide in a vice. Protect the slide from scratching. I would use a taped up punch to drive the sight off. Drive it off from the left side to the right. If you make sure you check the tape after each hit, and get no metal to metal contact, you should not cause any damage to the sight. Don't pound on the thin base of the sight. Place the punch on the thicker part above the lower lip. It does take some hard hits to get the sight to start to move. It also goes back on just as hard. I tried oiling the sight to get it back on. This did not make it any easier to get it back on. After having to take it off a few times, it did get easier to remove and replace. S&W does sell replacement stock sights, just in case you slip or? Make sure you don't slip and mark the slide.
I have a slide disassembly video that shows the sight removal, starting at 4 minutes and 30 seconds time frame:
M&P Shield Slide Disassembly - YouTube
Bob