We all know that each rifle is different !
My old Roberts liked 46 Grains of H-414 over a 100 grain Barnes triple shock.
My New one might like it too, i just put 20 together with 45 grains to try, as well as 20 100 grain speers over 46 grains of IMR-4350. I also bought a box of Hornady 117 grain ST super performance loads to try. I have all sorts of 25 caliber bullets to try. But will likely stay with a 100 or 110 grain bullet. I like to bet around 2900 to 3100 fps. Do you have a pet load ?

the Hornady 120 on top of RL-19 has done very well for me.
in one of my other ones the Remington 86gr bullet has done some nice work on top of 4895 it's just loafing along at 2400 fps but works on small game up to yote size like a champ.
[this is the one I generally keep in the truck]
if I wind that bullet up to 3-K to duplicate the old 250-3,000 load it performs just like it did 80 years ago.

I found IMR 4831 with 90 and 100 grain bullets to be a totally acceptable load. Start with 47 grains and work up. I had no adverse pressure signs with 49 grans +.

For 100 grain bullets I've foumd IMR4064 to be exceptional and Reloader17 great too.
For 110 and 117 grain bullets IMR 4350 is by far the best and RL17 works good.

Mine seem to like 120s with H4831.

Several years back I got 3000 Remington 120 gr PSPCL .257 bullets. I haven't found them to be as accurate as the Sierra 117 gr SBTs but they have been accurate enough and their terminal performance on deer has been quite good- being used in both Roberts and Ackley Improved versions. I have used them in the Weatherby but the accuracy drops off as it appears they are spun faster than the construction allows and I haven't shot anything with the RPs, preferring to use a Partition for deer.

47.5 gr. IMR 4831, 100 gr. Rem core-lok. Just slams Texas whitetails and shoots sub-1".

My favorite bullets a 115gr Nosler Partition, also the most accurate. Best powder for me is Norma MRP. I load the MRP to 3125fps or so.
RL23 is very accurate and gives at least 3100fps. Rl26 gives very high velocity, but no as accurate. RL22 works. RL17 is good as is RL16. They can be used for lighter bullets also.

Gun truck
That,s screamin fast for a 115 in a standard Roberts. Its your rifle but i am not pushing mine that hard. I would be happy at 2900 with a 115. I got 3149 from a 100 grain barnes saturday. fast enough...

43 grains of H4350 and the 117 of your choice. I like the SGK and Hornady IL. In my Remington M7 Mannlicher that loaf is good for 3/4” groups at 2,800 FPS.

Good luck!

No one has mentioned any IMR4350 loads. I know it is temperature sensitive and all that but, cold or hot, my M700 Classic shoots many sub one inch groups with 100 TSXs and 47.0 grains of this powder at around 3100. It does almost as well with standard 100 Hornadys.

In my Argentine Mauser-actioned, Douglas Featherweight 22" barrel throated to allow 3" OAL, 44 gr. of IMR 4350 with a 100 gr. Nosler BT generates ~2900 fps, generally puts 3 into an inch or slightly less at 100 yds. Sure, I could hot-rod it another 150 fps, but that duplicates the normal factory load and does everything I have needed from the .257 Roberts.

Clarence

TJ Roberts, my model70 24" barrel is about a hundred fps faster than other. I easily get 3125 fps with Norma MRP RL23,RL22. RL26 is close to 3190fps. I use Rl16 and RL17 with my 100gr loads usually with Barnes TTSX bullets.