Re: 280 rem?
Lend me your gun and I'll promise a couple winners for you.
IOW, only your rifle will tell a good load in your rifle.
You've got plenty of time.
Buy a box of 120 g Sierras or Remingtons for next to nothing and have some fun developing loads. Try 50-56g of 4350 or 55-61g of 4831.
If you go for something bigger, like a 150g, don't be scared to use some of the slower than normal powders, like RL 22, H-1000, though I believe 4350 is one of the darling powders of that cartridge.