Re: 260 load for the 120's or 123's only
Can only quote data from the Hodgdon manual for 120gr SPR SP's and 125gr Nos Partitions in a 24" 1:9" barrel.
The best velocities appear to be gotten with H4350 and H414(aka W760). The max/mins are:
120gr SPR SP
H4350 43.5gr/2814fps/51,400psi 46.5gr/2960fps/58,200psi
H414 42.5gr/2802fps/51,000psi 45.5gr/2968fps/58,600psi
125gr Nos Prtn
H4350 41.0gr/2714fps/50,900psi 44.3gr/2867fps/57,900psi
H414 40.0gr/2691fps/50,500psi 43.0gr/2852fps/58,100psi
H4831 45.0gr/2725fps/51,600psi 48.0(C*)gr/2862fps/58,000psi
My experience with H4350 is that it's well behaved and seldom has any nasty surprises for the .260 handloader. My experience with Scenars is that they tend to show/generate more pressure than Sierras of similar weights. I might also suggest 120 Nosler Ballistic tips. Most of my earlier data with them has been lost, but they were extremely accurate and totally devastating on 'Chucks. They did not perform well for me in a 1:8" barrel at high velocities and long distances, and my suggestion would be to try them with a 1:9" or 1:10" twist for best LR results.
Hope this helps.
Greg