My .257 Ackley Imp Roberts liked H4831 along with IMR 4350. With 100gr. Noslers, it got 3,484fps and with 120's, it managed 3,227fps. Bench accuracy at 300 meters stayed under 2" with both loads, which made me very happy. Barrel length, 26".
A 26" .257 Roberts will easily make 3,200fps with 100gr. Noslers or TS's.

In 1978 I chronographed a fellows custom .257 Weatherby built on a ZKK600 action (or 601 - '06 length anyway). he was using a book load supposed to produce 3,800fps with IMR4350. (I know there are much better powders today - and then) He had to use a piece of 2x4 to open his bolt - that chrongraphed 3,482fps - & was only one I'd shoot.

To prove my pressures were in line, while his obviously were way to high, I removed the extractor and fired another round, opened the bolt, stood the rifle on it's butt and a gentle thud on the table and out dropped the empty. I had a fast barrel, while his was a slow one - obviously. We were both using IMR4350 - but my load was about 15gr. to 20gr. less than his. If memory serves - off the top of my head, I'd say my load was 53gr. IMR4350.