A couple of years ago I bought a G & H side mount base to replace one that had been removed, leaving 5 ugly holes in the receiver. This was for a 1922M1 Springfield but the same would apply to the 52B Sporter. The base was oversized and flat on the side that fitted the rifle. It had to be contoured to fit whatever rifle it was to be mounted on. A new base can be cut down to fit whatever cutout there is in the stock. G & H still has the bases.