I had a 24" barrel from T/C (made back when they were a standard offering) that I tested with about 12 different bullets and all available factory loads. After testing for accuracy, penetration, and long-range expansion, my favorite all-around hunting bullet for the 260 is the 125 grain Nosler Partition, closely followed by the Hornady 129 grain. I would avoid the 140 grain Nosler Partition, as my samples didn't expand evenly at long range. They tumbled and lost their rear cores, failing to drive very deep. They're perhaps better suited to 6.5-06 and larger cases.
The Hornady 160 grain round noses work great in the 260. Velocity isn't much to brag on, but it doesn't have to be.
The Nosler 100 grain Partition is good for young shooters that want to hunt deer. It will kick like a .243.
For varmints, as long as you don't want the hide, I like the Speer 90 grain TNT. Muzzle velocity can easily surpass 3200 fps with several powders, and performance is pretty spectacular.
H4350 is my favorite powder for most bullet weights, as it gives good velocity and doesn't react much to changes in temperature.
