It's been many a long year since I reloaded for the 7 Mag but I always got superior accuracy from the 154 gr Hornady Spire point bullet, and superior big-game killing power using the heavier Nosler Partition bullets. My 280 Rem especially likes the 160 gr Nosler Partition. I've found the 154 gr Hornady to give gilt-edge accuracy in a variety of 7mms including many many military Mauser 7x57s as well as the few sporting 7 Mags & 280s I've owned. In my experience with my rifles it's been fully as accurate (up to 350 yds at least) as the 168 gr 7mm Sierra Match King.

The 154 Hornady is an adequate game bullet but the heavy Nosler Partition is much superior IMO. I've killed deer with both but prefer the Partition because I like the complete penetration combined with the violent expansion of the nose, seems to give the best of both worlds. YMMV of course.

Powder is another matter. You may find that the break-open action will stick with certain powders, even at seemingly fairly low pressures. This is a clue for you to try powders at the other end of the burning spectrum, i.e. slow-burning vs fast-burning. This has been a problem in the past with the TC single shots using in particular the 6mm PPC cartridge. You may not have any problems though, I hope not.
Good luck, Joe