Herne, I am sitting here with a batch of 125gr Nosler Partitions and a box of 129gr Hornady Interbonds, I want to do load development for one of these bullets to use this season.
I have no powder. I had enough Re 17 for about 35 rounds, so I used it up on a known good load for 120gr BT's so I have about 50 rounds that will keep me going for another month or six weeks.
I have being trying to get either Re17 or 4350 for nearly two months, my dealer keeps promising "next week", I should get some re17, next week. 17 really is the nutz in the 260.
Ref best loads, I found my 260 did not like slow powders, tried both N160 and 4831 when I first got it. Funny, I was getting reasonably consistent velocity, but the accuracy was not there, very inconsistent. Mine was also throated pretty short with a minimum spec chamber, I cna't even chamber 140's with setting them away down into the case.
When I moved to faster powder - Benchmark and Re17, groups dropped to really consistent sub .5" for 3 rounds.
Try a faster powder with 120-130grain bullets.
Another pal of mine has a 260 on a custom action, his is throated longer and shoots the 140 Partitions like a dream, he has taken everything up to Wildebeat and I think Zebra with it. It is a pure "meat gun".