Re: New 6.5 build
While either cartridge will do for 700 yard work, I would lean towards the 6.5x284. While you might be able to approach equivalent velocities, in my experience, the 6,5x284 case design seems to hold up much better than the 260 (I use mostly Lapua in both cartridges but applies to other brands). Loose primer pockets and thinning of the case head area can plague the 260 after very few loadings when subjected to the top end of it's pressure range. This will be necessary to approach 6.5x284 performance, particularly if you want to take advantage of the 140gr bullet ballistics. I agree that you should go with a long action in the 260AI for versatility with bullet styles, and would recommend a 1:8 twist in either cartridge. IMO.
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