Originally Posted by lazylabs
The ones you mentioned are all really based off the same case and will be more or less the same. The 284 case will also be close with a shorter case and possibly more room to seat bullets depending on what action/stock you are using. It really depends on what you want to shoot and how far. There are lots of other choices also, the 6.5X47, 260, 260 improved, 6.5 WSM or WSSM, 6.5 x 55, 6.5BR are all fairly popular. It really depends on your plans and how much case work you want and if your willing to change bolt face sizes. If your looking in the 06 case capacity range the 284 is hard to beat with brass available and a very good track record. Pick a bullet you want to shoot, speed you want and that will help you pick a case size. It might also be a cost consideration with what reamer your smith has on hand. If you decide(or pass on) what your shooting, how far and how many rounds you want your barrel to last you can get more specific info. just my .00002 cents
I have two .260s, a 6.5-284 and a 6.5-300 Weatherby. Might be obvious that I like the caliber. . .
Were recoil no issue, as in an occasional use hunting rifle, I would likely move to big 7mm or even .30mag for the longest range stuff since both wind and energy are better, but I shoot a lot. By the time you drive a 7mm/175 or a .30/210 at the near 3,000 fps needed to match the 6.5's trajectory, recoil is getting "noticeable".
IMHO, the 6.5-300 Wby I have is much like Fiftydriver's big-cased 6.5 version: a finicky barrel burner that needs cleaning VERY often. IMO, not very practical if you want to do anything but hunt with it. Mine had a 30" barrel, which had to be set back at 750 rounds, and now it's 27". It needs very slow powders (Retumbo at the fast end, H-870 for best velocities with 140s) and cleaning every 20 rounds or so to keep from running high pressures due to carbon fouling in the ball seat area of the throat. The good news: It delivers over 1,000 FPE at 1k yards and kills deer like lightning . . .
The .260 isn't a bad cartridge, but IMO, is not quite enough capacity for the 140 grain bullets that make the 6.5 so ballistically efficient. The top velocities with normal barrel lengths and 140s will be about 2,850. Black Hills is custom loading match ammo for GA Precision Rifles with a 139 Lapua Scenar at 2,850 that is shooting at less than 1/2 moa in my Broughton barrel. I will use Lapua 123 Scenars in mine for UKD match shooting, and should get 3,000 fps with them pretty easily.
The .260 AI would be just about enough to run the 140s well, but at that point, I might as well go for another 100 fps and to the 6.5-284, which I did.
The 6.5-284 has been a good balance of velocity and maintenence for me. I am shooting one in a Remington long action, and can seat the longest bullets out where they need to be w/o feeding or mag length problems. I can shoot 100 rounds or more in a day w/o cleaning and with no pressure problems. I get about 2,975 FPS with 140/142 grain bullets and moderate loads and my first barrel began to lose accuracy at 1,700 rounds. I went on shooting it, and it was tossing 2 fliers out of 5 shots toward the "end" (2k+). I have since rebarreled the rifle to the same specs w/o giving it a second thought. The fact that factory loaded match ammo is available for it might be a plus for some folks too. I got 1/2 moa accuracy with Black Hills 142 moly and placed 7th, 5th and 9th (of 30-34 shooters) in several of the Allegany Sniper Challenge matches with the BH factory ammo.