Re: 260 REM barrel twist?
I've been shooting .260's out of factory and custom 1:8" barrels for over half a decade, and honestly, I can't say.
Performance with 142SMK's at 2850fps and going the distance at 1Kyd strongly suggests that the twist works, and mildly suggests that maybe a bit less might work better.
Trying 120 Nosler Ballistic Tips in the 28" 1:8" barrel gave such disappointing 1Kyd results that I was left to wonder whether a 1:9" or even 1:10" might be better. Works great up close, but way further out, nearly double the predicted drop and drift with obvious signs that the bullets were not impacting nose-on, giving suspicions regarding overstabilization. But I can't say anything with certainty regarding that anomaly.
Trying 95gr V-Max in the 28" 1:8" barrel worked well with a tuner at the Hodgdon published minimum (47.0gr H4350) load, and load testing much nearer max with R/S Big Game suggests that my concerns about centrifugal detonation were misplaced. I have no idea what the velocities are, but I think they can be conservatively estimated at 3400fps or more. Accuracy appears to be an attainable goal.
For me, it's a crap-shoot; but so far, it's also being an enjoyable one.
Greg