[mapsjanhere]

Your problem is the .530 bolt face - that's the magnum size, so there are very few target cartridges in that range. You might be able to try some rimmed cartridges like the 30BlaserR or 7x65R, but they're not really all that much weaker than a 308 NM with moderate loads. OTOH, a new bolt for a 1903 cost $25 at Numrich, so your rebarrel might as well include a fresh bolt face, allowing you to pick anything with a standard .47 case - use a 8 mm Kurz if you want unusual and easy to shoot.