Hello LouM,
A stuck butt plate is not uncommon especially when it was fitted properly. What I have done in the past is to strike the centre of the butt plate with a rubber mallet. This often 'shocks' it loose. Sometimes these butt plates are quite literally glued in position especially when the butt plate was screwed into position before the stock finish was applied. The finish would creep by capillary attraction through any minute gap between the butt plate and its seating. Over the years it would harden into a glue like substance.
A blow or two with a rubber mallet won't damage either the butt plate or the stock. If that fails, then try bending the tip of a small screwdriver to a 90 degree angle, insert it into one of the screw holes and try and push the tip between the underside of the butt plate and the stock. This may put a small mark on the wood, but it will be out of sight once the buttplate is refitted.
Take it gently and you shouldn't have a problem. Whatever you do don't stick a chisel, knife or any other object into the side of the butt plate/stock. You may get the butt plate off, but it will look like a burglar has used a jemmy on it.
Harry
