ajax be sure to consider barrel life quotations on an apples-to-apples basis, and also remember that a big 7mm magnum is simply an *incremental* step away from a big .308 magnum. So the *good* things will change only incrementally (you'll get a *bit* better wind drift performance, a *bit* less recoil, etc), and the *bad* things will also change only incrementally (a *bit* less barrel life)
The 700-1000 round barrel life figure you were quoted is on the short side of what might be expected, and probably makes sense only with the biggest cases and the *most* demanding accuracy requirements (e.g. world-level F-Class rifles). With those same requirements, a same-capacity .308 magnum would have *somewhat* longer life, but not vastly more - as a SWAG, if 75 grains of powder behind a 7mm (.284") bullet is giving you 700-1000 rounds of barrel life, then 75 grains of powder behind a .308" bullet might be expected to give 800-1200 rounds of barrel life. A step in the right direction to be sure, but *NOT* a night-and-day difference. You are *NOT* going to see 3000 rounds of barrel life out of a .300 Win Mag versus 1000 rounds of barrel life out of a 7mm Rem Mag - those are not apples-to-apples figures. Either one of those barrel life figures may well be correct for a particular set of criteria, but they won't *both* be correct with respect to the *same* criteria.
BTW what is the "really long range" that you want your rifle to perform well at? You have said 1500 yards, but are you sure on this? 1500 yards is a long way out, and is a different class of problem to solve than 1200 yards, or 1000 yards, or 800 yards. Each of these steps is a bigger and more expensive problem to solve. If you overspec the range, you'll end up having to overbuild your rifle and that not cheap (if you really wanted to Do Not Pass Go, Do Not Collect $200, Go Straight to .50 BMG, I'm sure you would have just said so... ;-) If you really, truly want good 1500 yard performance (and what is meant by "good" needs to be fully pinned down - accuracy? terminal velocity? terminal energy? terminal super/sub sonic?), you'll have to *pay* for it, not only in dollars (but *plenty* of those!!!), but also in overall utility of your rifle - a 24# rifle that truly accomplishes your 1500 yard requirements, is a mighty PITA if all you really needed was the same requirements at 1200yards or 1000 yards (and you've already told us that you want the rifle to be around 16#).
The first rule for long range performance is pretty simple, it's "bigger is better" (this isn't the only rule, but it is the first). Of course bigger is also more expensive, more difficult to shoot, less generally practical and flexible etc
Why not consider a 7mm cartridge in the 7mmRemMag class, i.e.75-80 grains of powder, firing a Hornady 162 AMAX @ 3100fps or a Berger 180 VLD @ 2940fps? Using a 1-10" twist barrel, both are comfortably stable. The 162 AMAX goes subsonic just before 1550 yards in a std. 59F sea level atmosphere, the 180 VLD goes subsonic just past 1575 yards. At 1500 yards they are giving 162" and 153" (respectively) of wind drift in a 10mph crosswind (and 59"/57" at 1000 yards, for comparison purposes - i.e. this is a pretty hot performer!). Compare this performance to a first-rate .308WIn tagrget rifle, e.g. Berger 155.5 Fullbore @ 3000fps - it'll go subsonic just before 1150 yards. The .308/155.5 will have 251" of drift at 1500 yards (where its speed will be 950fps), and will have 91" of drift at 1000 yards.
Basically, whatever a .308/155.5 will do at 1150 yards (speed=M1.0, drift=11.3 minutes), a 7mmMag/162 will do at 1550 yards (speed=M1.0, drift=11.3 minutes). What's the price to be paid for this extra 400 yards of performance?
- The guns themselves will be the same cost (actions are the same cost, barrels are the same, stocks are the same, gunsmithing is the same).
- Recoil and/or gun weight will be comparable; the 7mm/162@3100 will be generate 35%-40% more impulse than the .308/155*3000, which you'll either soak up as increased recoil or increased rifle weight, or some combination. I'd expect either to be eminently shootable or luggable.
- ammo costs will be comparable, to a first approximation I'd call them the same. Primers are the same cost per shot, bullets are pretty similar, brass is pretty similar (per-shot, about the cost of a primer), the 7mm will burn about 75/45 times as much powder, that's about 13c/shot more of $30/# powder.
- barrel life. If barrel wear scales linearly with charge weight and inversely with bore cross sectional area, then the .284"-75 grain cartridge will have roughly 50% the life expectancy of the .308"-45 grain cartridge. So if a .308/155 gives 3000 rounds of acceptable accuracy, the 7mmRemMag will give about 1500 rounds of the same accuracy (you can do the math for other accuracy thresholds). I won't do the math on dollars per shot of barrel life, that's something that every rifle builder should do for himself and get a good feel for how much (or how little!) the price of barrel wear actually is, so that he can intelligently make barrel life tradeoffs that are right for him.
There's one last thing to consider, and that is that the 7mms presently enjoy an unfair advantage over the .30 cals - the very best 7mm bullets that are offered today, are somewhat better (dragwise) than the very best .30 cal bullets offered today. That can and no doubt will change (if and when you hear Berger announcing a .308 230-250 grain VLD, you'll know the day has arrived), but until then the big .30s are somewhat handicapped in delivering their full potential.
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