.257 Roberts powder???

[Rifleman97]

Not sure how big the case capacity difference is between the bob and the bob AI, but the Bob AI I had for a couple years liked RL19 and H4831

 

[rabbit55]

The 257 likes the slower powders. If you can't find some 4350, W760 would be my next choice. With W760, I prefer Winchester primers for best light off, particularly if hunting in cold climates.

 

[VinceMule]

AA4350 is a tad slower burning than the H4350, it would be on my list to try as the Heat Index on the powder is cooler.