Re: NEED HELP FROM YOU SHOOTERS OUT THERE!
Well, I'm no expert, unlike some of the other guys here, but I'd make the following observations:
If all the scopes, and all the ammo you try perform pretty much the same way, they're probably not the problem. I think you already figured that out.
If there is a problem w/ the bases, I think which way the bases sit is the least of your worries. I've used the bases like that several times, mainly in an effort to move the scope forward for more eye-relief. Never had an problems. I'd be more concerned w/ whether the base screws are tight. Then I'd make sure that the windage screws on the rear base are tight, and that the front ring pivots in *tight* into the front dovetail. I've had some really bizarre groups from a gun where the front ring didn't get really tight in the front doevetail. It basically turned w/ minimal finger pressure, rather than needing a ring wrench or dowel of some sort.
Next I'd check that the action screws are snug. No need to gorilla them, but they do need to be fairly snug. There may be something funky in the bedding.
Have you shot a magnum before? You say that you know the gun should be capable of 2" groups @ 200yds; is this from you shooting it, or someone else, or just your gut feeling? If you aren't experienced w/ shooting guns that recoil heavily, the shooter can be the real wildcard. I know that I am [img]images/icons/wink.gif[/img]
If all else fails, enlist the help of a friend, preferably one w/ experience shooting magnums, and have them try it, just to make sure it isn't you.