I have a couple boxes of these bullets and I plan to try them. To this point I have tried 100, 115 & 117 gr. bullets in my Roberts with groups ranging from 1.25" to .4"(when I do my part). By far the powder my rifle likes is IMR 4350. I have also tried RE19 and H414 but IMR4350 is always performs better.

For the 90 gr. Bullet, I'm thinking that 4350 may be a little slow. I was thinking about trying IMR 4064 first. What's some of your pet loads for this bullet? Thanks.

C-ROY

The 4350 will probably be your best powder! I use 4831 with both the 87 grain and 90 grain and it seems to work. Good Luck

4350 is a good bet.

You might also try either IMR 4831 or AA 3100 (same thing w/ a dfferent label. The previous poster did not specify, but I find H 4831 both a little slower and a little bulkier

C-Roy: I am using IMR 4064 in my Mdl.70 Pre-64 in 257 Rob. 42 grs. and am getting just under 1" 3 shot group using the Sie. 90 grHP. really like the load and hoping to try it out this year on varmints and deer. I am going to try Varget also.
good luck with Yours.
Navarro

I like Reloader15 and H380 for 75-90 gr in the Roberts. Velocities in the 3200 fps range with RX15, sub MOA in a Ruger#1. FWIW, the 85 gr Nosler BT is far more accurate than the Sierra. Velocities about the same with both of the above powders, 3400 fps+, shooting in the 5's. Recently did 22 shots in .77" with H380.

Nah, if 4350 has been good so far, it will still be good with the 90 grainer. Years ago, when I had a .257, I loaded it exclusively with Surplus 4831 (the slowest of the 4831's, almost as slow as IMR 7828). I had one of the first Oehler Model 10 chronographs and got excellent velocities with the 90 grain Sierra (as also with the 117 grain Sierras).

Nah, the slower powders aren't as accurate, even with mag primers. Lots of velocity variations. Might go a bit faster but not much, especially with light bullets.