I have asked similar before, but now I am about to load my test loads this weekend and hate going in blind.

Here is the loading data from Hodgdon's website for my selected powder and bullet for .257Roberts. Notice that it is a conservative load meant to be safe for older Mausers. I am loading for a modern action and with +P Brass. I am looking for loads to make the most of the round's capabilities. I would like to see if 3200fps (maybe 3250?) is attainable with this bullet/powder for a longer range predator/deer load.

Bullet wt/ type- 100 GR. SPR SPBT
Powder - Hodgdon H414
Caliber- .257"
OAL- 2.770"
Starting load/ Velocity/Pressure- 44.0/2919/33,600 CUP
Max Load/ Velocity/ Pressure- 45.0/3098/44,500 CUP

I know precision will dictate the final load, but I would like a good modern maximum. I want to load for the strongest load that holds a decent group. If I can go up .1gr and give up just .1" in group then I would if I can put a bit (worthwhile and noticeable via chrony) more energy on target.

Just looking for input.

Jim Kobe built me a very nice 257 on a 09 Arge and as usual I did alot of research b/4 working up my loads. Based on Hodgdon, Alliant, Ken Waters, Nosler, Lyman, Speer and John Barsness handloads that work--from Rifle/Handloader, I settled on H4350 w/ 100g bullets, WW brass & CCI br primers. Started w/ 44g and worked up to 46.5g. This load shoots very well and chronos 2990 . I think your 3200 is optimistic, but may be doable if you load to much higher than listed pressures for the 257. MAybe at 6mm Rem pressures. Be cautious, pay attention and use a chrono.

Well, I have a 26" barrel too, so it might give me an edge on the speed. I thought about 4350, but I am a bit over the posted max velocity even with the Varget load (within specs) I currently use.

I know I am good to 50k on pressure. But how am I to know before I throw the rounds down range and measure my case heads?

I think 3250 might be a strtch but not by much.I have the ackley improved version and while I can easily reach that and more but I have been fireforming brass and playing a bit and i think you can try several other powders rl9 rl22 mrp might be a little slow but might surprise you. I have not tried h4831sc to fire form but you might give it a try. i think the books are a little cautious on the 257bob and if i had it to do over I would not improve. If i try some of the hotter loads i will send you what i get and i lose a little of velocity fireforming.

Start w/ the loads in the manuals recommended and work up from there using your chrono. Barnes first manual has 257 velocities a good deal faster w/ similar powder charges than any other source I've seen. I believe the barrel in the Barnes loadings was 26.I do not believe the Barnes manual list pressure for their loads. Their current manual(online) list 100g bullets at 3124/3126fps w/ Imr 4350 and Hunter w/ a 24 in barrel

I want to try the AI someday, but my financial manager (wife) says not until I wear out this barrel.