That was my third (3) one that I personally barrelled and a few other factory chamberings I've reloading for, and I not saying I'm an expert just given my opinion. But I figure that Shilen has worked with more than most gunsmith shops, and their recommendation is a 9 inch twist for bullets heavier than 100 grains. It's just been my experience that a 10 inch twist usually shoots 100 grain bullets more accurate than 117s or 120s. I even tried the 110 Accubonds and 115 Noslers, and 100s beat those too. Most factory 7mm are 9 inch twist, 6.5mm is usually 9 or 8 inch twist, because of their long for bore bullets. I don't think a faster twist would hurt. If all I wanted to use was 100 grain bullets I'd probably just use a 243.
