I would try R26 go with the Alliant data, it is a winner in my rifles. Just run it up to max and then start adjusting the bullet jump is all I needed to do for mine. The FC has a 1-8 twist I believe and is perfect for the 105s-108s not sure about the Sierras or the 115s in a 1-8 but will try them at some point. The 110-115s may be iffy.
That rifle deserves good brass, I would stock up on Lapua if I had it to do over again. Currently I have probably five different manufacturers brass and this doesn't help consistency. If I were smart which I am not I would scrap all the odds and ends and get Lapua.
1:7 twist for their 243 (and 6 Creedmoor).
