I am anticipating the arrival of my 505 Gibbs CZ Safari Classic, bought on the AR classifieds a couple weeks ago.
I have a supply of Jamison brass, RCBS dies, and 600gr NF solids coming.
Franz at NF has suggested 121 gr H4831sc for 2150fps. I plan on trying it.

There has been mention on the forum of 4831 being a bit slow for the 505, and was wondering if any of you have a pet load for the 505 with 600gr bullets, NF or otherwise.

I have no interest in hotrodding it, 2150 of so seems like a great plenty.

Marty, I have used slow powders some in the 505. I like medium propellants though. Woodleigh 600pp with 110 gr. of RL15 and 5/8" long chunk of 5/8" dia. backer rod gives 2170. I don't know how the NF would perform.

525 gr Barnes with 135 gr of H4831 went 2281 but kicked significantly harder than loads generating similar velocity with AA2520, RL15, IMR8208 and TAC and the velocities were uniform. AA4350 acted about the same as H4831.

For more velocity (over 2200) I would go with the slow powders because the mediums would give too much pressure. 2150 fps with a 600 is quite comfortable with mediums.

I have been experimenting with 600gr Woodleigh PP's and the fastest powder I use is H4350, 135gr (no filler), am trying RE22, RE25, H1000 and Retumbo. All of these powders will produce velocities in the 2150fps with ease, but I'm looking for 2350fps+ with higher pressures and better loading densities. I am not a fan of using filler, so the above powders will be the best case fill.
RE15 is too fast for my liking, as was Varget and 760.

Hope this helps.

Cheers.