Hello Benchshooter;

Lee has a website that will allow you to order from them directly. If this won't work, give them a call. They are great to deal with. I live in Canada and have never had a problem getting stuff from them. Even when I had to send dummy rounds across the border. Any delays were government related. They were fast. I don't like their lock rings so I use RCBS instead. Huntington's Reloading supplies can help you with large bore stuff from RCBS.

Reference manuals that have 505 Gibbs data include the latest Barnes manual(this is online), Hornady's 9th edition, Norma's Reloading manual, Pierre van der Walt's African Dangerous Game Cartridges manual, the A-Square manual, and the hot off the press, Woodleigh manual. I just found out about this an hour before I started typing this.

In the older Norma manual they list 140.4 grains of very slow burning MRP-2 with the 525 grain Woodleigh FMJ. They list 153.0 grain with the 525 grain Woodleigh RNSN. They use Norma brass and Winchester magnum caps. Velocities run 2277 and 2415 respectively. Note the extreme difference in powder charges between the Woodleigh soft and solid loading. These are the only loads listed. There were no loads other than these listed. Even with my 458 Winchester I have to load the Woodleigh 500 grain FMJ 1.2 grains less than the 500 grain soft. I get the same velocities and the bullets hit the same hole at 100 yards. With Hornady's I use the same load.

Pierre van der Walt chronographed the Norma 600 grain load in a rifle like yours and got the claimed 2100 fps. He pulled a bullet and got 128.0 grains of a propellant that looked like IMR 7828. This powder performed like the IMR 7828 as well.

Pierre van der Walt loads 525 grain slugs with 140-144 grains of IMR 7828. 140 with the solid and 144 with the soft and you should be okay. This last sentence is my own. I don't mean you harm. With Hornady 525 grain bullets, they start at 131.6 grains of IMR 7828 and stop at 140.1 grains of IMR 7828 at a top speed of 2250 fps.

What ever powder you use is your business. I would contact the powder manufacturer and ask them what they would suggest. These guys know what works. Alliant Powder or Hodgdon's Powder both will answer your request. I would reckon that this will break up the monotony of their day.

My best wishes.