As a long-time fan of the .577 Light Nitro cartridge, I must add my congratulations to the above.
What a lovely rifle, you will have a ball in the hunting field with this beauty!

TH44: as an aside, I'd be interested to hear details of your problems with H4198, which is our AR2207 here in Australia. Perhaps in a PM so as not to detract from Hubert's marvelous acquisition. I would have thought this powder to be a bit fast for the 650gr bullet, lot of inertia there to overcome before things get going. AR2207 was recommended to me by the previous owner of the 'Fat Lady'. Notwithstanding that Hubert's results on paper speak for themselves, I couldn't get it to work in the big Greener and found success with our H4895 equivalent.

Just one more thing: the backer-rod we buy locally is white closed-cell plastic of some sort, whereas that pictured above is the silver-grey polyurethane foam (like speaker-foam) and is far more compressible. Not sure what is available in the US, perhaps someone can clarify this? Our white backer-rod works, but I personally prefer saddle-felt wad-punched from 1/2-inch sheets. More traditional, won't go gooey in long-term storage in the tropics, and no spike on the front of the pressure curve (noted by Sherman Bell: "Finding out....").

Apologies for the over-long post: again, paradox, ripper double mate, g'donya!