RE: 257 roberts
I had a Remington 700 Mountain Rifle chambered in .257 Roberts. It shot like a dream, but it was a short action. To get the accuracy, I usually had to seat the bullets out far enough that they would no longer fit in the box magazine. The rifle favored the lighter bullet weights. It shot the 85 - 100 grainers very well, but the accuracy of the 115-120 bullets often left something to be desired. My best loads used IMR 4350 and Nosler 85 and 100 grain Balistic Tips. The 100 grain Hornady spire points also shot really well.
I sold the rifle before moving to Alaska. In hindsight, that probably wasn't a great move. I will have a heck of time finding another one.