Terry Leonard makes a 600 Yd. stock. Dan Killough has an exclusive on an altered version of the McMillan Edge with a straight line butt, parallel to the forend. He markets primarily to rimfire shooters, but the stock is perfect for 600 Yd. guns and is available in 3 weights, the heaviest of which is a solid fill. He usually has some in stock with a "Basic Inlet" that does not have any bolt holes or trigger guard mortise and can be opened up to accommodate most BR actions.