Originally Posted by Fastbolt

Don't use a rubber mallet to remove the sideplate for repair. The soft rubber will cushion the blow against the pin's head more than a simple hard plastic mallet. A hard plastic yellow plastic mallet from a hardware store was what came in the older armorer kits. (Now plastic & brass combo hammer, I think?)

You only need to "snap" the left end of the sear pin ("Headed" end) to the right, down flush with the left side of the frame, to clear the old sideplate.

With a normal sideplate that isn't broken, a simple short brisk "whack" to the left end of the sear pin, with the plastic mallet, will snap the pin out from between the legs of the sideplate, putting it flush with the left side of the frame.

Besides, from the pic you posted of your 4516, you don't need to move/whack the sear pin, anyway, as the rear leg is already broken off, freeing the sideplate from being captured by the sear pin's "headed" end. You can simply rotate the front leg slightly forward, if need be, away from the pin.

When installing a new sideplate it's also important to make sure the right end of the sear pin is flush with the right side of the frame, the "headed" end of the pin (left) sticks up out of the left side of frame far enough to properly capture the legs of the sideplate. This is easily done by sitting the right side of the frame on a hard, flat surface (or on top of an armorer's block or wedge (aka - maple wooden door stop). Just like when you support one side of the rear/bottom corner of the grip while installing the grip pin (more simple whacking with the yellow plastic mallet).