Not knowing what you really want it pretty normal. Heck, that's pretty much how I ended up with so many rifles
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The '06 used to win a lot of 1,000 yard matches, way back in the day. Great hunting round. The old war horse can do just about anything you want it to do. It uses a lot of powder and has a bit of recoil for doing a lot of informal target work though. The .308 as Bob just said, uses the same bullets, but is easier on the shoulder and pocket book, most guys feel it has an accuracy edge over the '06 too. For what I "think" it sounds like you are leaning towards, the .308 might be a more practical choice. Put it this way, I'd bet you'll be able to shoot it better, due to the lesser recoil, if nothing else. Bolt guns chambered in .308 are usually short actions, too, while the '06 is always in a long action. The short action is more rigid and has more inherent accuracy potential.
Really though... If this is primarily for target work at distances over 400 yards, I'd suggest the .260. Same case as the .308, just a smaller diameter, ligher bullet. But, while the bullets may be lighter (and therefore less recoil yet), they have greater sectional density and B.C. That is to say, the heavy for caliber .260 bullets cut the wind exceptionally well. An awful lot of long range matches today are being won with .260's or custom 6.5 wildcats of similar capacity. One of my personal favorite long range rigs is a 6.5/284, which uses the same bullets as the .260 but has the powder capacity of the '06, but fits in a short action. Quite a bit of recoil and a lot of muzzle blast though, and it chews through barrels in a hurry too.
Nothing wrong with a .243 either. Or, for that matter, for economy, recoil, barrel life, easy shooting, that old .223 still ain't no slouch. It won't run with the larger calibers for wind cutting, but with 69 to 80 gr. bullets, it's not too bad either. I do like the .22-250 and the .220 Swift as well. I've worn out three factory .22-250 barrels and two custom .22-250AI barrels, to give you an idea just how much I like those cases. But, in a factory rifle, there aren't many fast twist options for these bigger .224 cases. Savage does make a 9 twist .22-250, but, for reasons that would take me too long to explain right now, for what you are looking to do, I'd stick with the .223 if you want a fast twist .224 caliber. Both of those custom .22-250AI barrels I wore out, were 8 twists, so I do offer that advice from real life experience.
That Savage you are looking at would be hard to beat for cost vs. out of the box accuracy potential. I prefer Rem. 700's myself, but, factory rifles are nothing but organ donors to me, I don't really concern myself with "out of the box" potential. Mainly, I like the physical size and the trigger options for the 700's better. But, if I were looking to buy a factory rifle to shoot more or less "as is", especially for the kind of shooting you are talking about, I'd be looking at a Savage.
A picture of a couple of my more accurate rifles, just for grins:
The one with the dragon painted on it is chambered in .22BR, the laminated stock in .243AI. They'll both put five shots on a dime at 100 yards, or into a clay pigeon at 500 yards pretty regularly.
You know what though? I really think that AR you've got will do just fine at 400 yards!
- DAA