A 3-9 power(9X) seems a little low to me to be shooting at 500 yds. You're gonna need a rock solid rest anyways so you may as well be able to see what you're shooting at and be able to shoot at a spot on the or animal rather than just shooting at it. I have a 4.5-14 on my 7 Mag and to me 14x is ok but I wouldn't feel over powered on magnification with a 6-18 either.
Oh I dunno. I checked zero on my '06 last night, then picked a gallon of wild blueberries while I was out there on the tundra.
Aim point was a white 4x5 1/2 inch card at 325 long paces, taped to a 30 inch square of brown cardboard. I forgot the rangefinder but was probably within 4 yards plus or minus. Rifle wears a 3.5-10x Leupold used on high, previosly (last November) zeroed at 300 yards. A 3 round group using only a front rest strung along the bottom edge of the card with only about a half inch vertical separation and about 5 horizontal. That was me of course. One shot at target out another 90 paces with a hold about one card height over the card and both a front and back rest (day and fanny pack) centered the card and I called it good enough ! 150 grain factory Hornady Superperformance with an advertised 3080fps.
Last year I popped two caribou maybe 2 minutes apart with the rig , using the snow machine windscreen for a rest ( forgot I had the Bog-pod with me. The first was an eyeballed 300 ( actually worked out to 290), the second was a ranged 433 yards, using line of back holdover. Both were double-lunged, one shot each.
I'd say a 3-9 scope will do just as well - ain't that much difference. I've never liked the 7 Mag personally, but it will do fine. It doesn't have anything ballistically on the '06 to 300 under hunting conditions but then it becomes marginally flatter after that, assuming similar bullet weights. It will kill anything at 500 that an '06 or 300 Mag will with proper placement.
