Two comments, first you need a sufficiently fast twist on the 260 rem in order to handle the high bc bullets, the 140s. I think you want a 1:9 twist for those. Talking about power, lets remember it is a 308 case necked down to 6.5mm. At long distances, the high bc bullets start to really shine retaining energy compared to the 30 cal 308 bullets. It is plenty powerful.
Also, the plain old 243 shooting the 115 grain bullets is a perfectly good target 1000 yard round.
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