Raisuli,the Roberts is a Junior Version of the 270 Winchester, and the same range of powders seem to work well;IMR4350 as you mentioned, H4350 as JB recommends,RL22,and back when we were running the cartridge a lot,IMR 4831 gave great velocities and accuracy with everything from 87 gr varmint bullets(app 3300 fps),up to 120 gr bullets, the 115 and 117's included.
I recall one Ruger M77 that broke 3000 fps pretty handily with the 115 Partition and IMR 4831.
I would not be shocked today to see 7828SC do a great job with the 115 and 117 gr bullets also,but have never tried it.
For me, I pretty much always used the 100 gr Nosler Partition, figuring if I wanted more than that I would just grab my 270,but if I were planning on making a 257 an all round rifle, I would likely load a 115 NPT to around 3000 fps and Talley Ho!
Last edited by BobinNH; 05/27/12.
