Counter sink a starter hole in the middle of the screw slot to keep the bit from wandering. Then start with a small bit and drill a hole for a guide for a larger bit. A 1/8" bit should be fine for the shaft diameter. You only have to drill about 1/16 to 1/8" deep to get to the screw shaft from the bottom of the slot. The head will pop off and then pull the lock. Or use the soldering gun heat method with the solvent. The plate bolster threads can't be more than 3/8" deep. Put some tape around the sideplate to protect the finish and go to it. Even if you mess up the screw head, a new one is only $1.50. It will cost almost $50 to mail the rifle back plus after this amount of time they will likely charge return shipping. Besides it is only a TVM rifle.