I WISH I had your problem...it would mean I owned a double. LOL

I'm shooting the 500 Nitro 3 1/4" in a custom barreled Ruger No.1 and I get great results with 570gr Woodleighs (softs, I haven't tried solids) with 114gr. H-4831 in HDS brass and Federal 215 primers. I don't have a chrono, so I have no idea what they're actually making as far as speed, but accuracy is great. You might want to try this powder and bullet, but again, I have no way of knowing if this particular loadwould be safe in a double, since the No.1 is so much stronger.

The data source, which I can't remember now, listed the following:
109gr. 2057 fps 31,800psi
112gr. 2115 33,700
113gr. 2150 36,300
114gr. 2175 37,000
115gr is max listed load.

Keep us posted, I love hearing about this stuff.

Cheers,
Rick