If the 260AI follows in the footsteps of the 243AI, you should get about a 1% increase in case capacity, about 5 grains, which would equate to about a 0.25% increase in velocity potential. The biggest advantage to going "AI" would be that the sharper shoulder will almost certainly reduce case stretching and increase useful case life. However, this is a "cost/benefit" balancing act. IOW, what will be the cost of X stretched cases to reach the cost of buying/renting a 260AI reamer and buying 260AI dies?
I think that the Remington 700 LSS MR format is about as close to the perfect vehicle for a 260 as can be found in a production rifle. Not too short, but not too long. Maybe a little heavy, but nothing that can't be easily fix with an application of McM Mountain Rifle stock in standard or Edge format. You can't go too far wrong with your 260 build in a Winchester 70 if you build it to mimic a Remington 700 LSS MR.
I have a variety of rifles chambered in 260 with barrels as short as 18.5", a Ruger 77 RSI and a Remington 7, to as long as 26", a Savage 11 with a Shilen heavy barrel. The 22" Remington Ti/MR contour balances nicely in the short 600/660, 7, and 700 Remington actions and will likely do so in your SA Winchester 70 action.
Jeff
