If you can find them...
CCI250- I've been looking for these for a couple of months
Remington 91/2M (I picked a box of 1,000 up at Bass Pro the other day. I was amazed to find them and it was the only box)
Whatever someone else recommends
you can get your hands on
The rifle won't go bang without them.
The Sierra manual says:
MagPro for accuracy
IMR-4831 for hunting (SMK's are not recommended for hunting)
Both are loaded for 3,000 fps. I assume that the difference is SMK vs SBT and HPBT bullets.
other choices are:
H1000 (good powder for the big magnums)
RE-22 (good powder for the big magnums)
There's more but those are the powders that I've used
If you don't have a local outlet for powder, Powder Valley is a decent source for online ordering. You have to pay a Hazmat fee for powder and primer shipments so it's not necessarily the cheapest way to go
PS- Berger VLD's are great bullets. Check them out. Sometimes Bass Pro or Cabela's has them. Look for the "pretty" bright orange box.