I am currently in possession of a custom rifle in .30-338 Caliber. The gun is my friends, but he wants me to sell it for him. He has been out of the shooting/hunting life for about ten years and is liquidating. He bought the gun just prior to this walk in the desert so he has only shot enough cartridges to sight it in. He can't remember anything about loading for it so I am at square one. I told him it would be a tough sell as it is a custom gun and we have no data on it, or targets to show us what it can or can't do. I told him I would work with it enough to obtain some data for potential buyers. Here is my question: Assuming the use of 180 grain bullets, and assuming that I have IMR 4831, IMR 7828, IMR 4350, H1000, RL19, RL22, and RL25 on hand, where should I start? Do I have optimum powders for this cartridge on hand, or do I need to look at other options? Any special quirks about loading for this cartridge? I have loaded for the .300 Winchester Magnum for years, and I assume it will be very similar, but if there is someone out there that has experience I would love to hear it. Thanks.