I don't know if anyone has tried this or not. But after shooting my 6.5-284 with RL25 I thought it might work in my 257 Roberts.
In my factory ruger #1B (26" barrel)with 52gr. (pured in slowly)-- I got 3078fps ES of 41 and SD 18 with a 120gr. speer flat base, Win primer Rem brass COAL of 2.85" with 0.90" group (ten shots). Nice!
Pressure wasn't bad from what I could tell. Easy extraction, no crater, no top hat.

Should work well in 257AI, and 25-06.

I haven't used RL25 in my 257imp. but RL22 has been a top performer with 117gr. SSTs in my rifle. I have a feeling that RL25 is a bit on the slow side for this case except with the heaviest bullets.
Elk country

MRP is the slowest I've used in my .257 Roberts, my barrel is only 22".

ras323, where did you get this load from? The Alliant site shows 44 grains of RL22 for 2785fps. You are suggesting 6 grains more for an extra 200+ fps. Admittedly this is from a 26" barrel. Mine is much shorter. Just wondering how you arrived at this load.
Peter.

Peter,
I made it up (educated guess). The Barnes manual lists RL22 @49 or 50gr (I think-- I'm at work). I use their data because their bullets create more pressure than conventional bullets and have been at or below max in my gun.
: I figured Rl 25 is slower than RL22. I Started one grain below Max RL22 and worked up. I didn't actually think I could get enough in the case to reach top pressure.
: I also read,somewhere, that Norma uses it in their 6.5-284 with 120gr. bullets. I thought it might work.
: I also got 3170fps (+/-)with 117gr Hornady SST's, 1.75" (5 shot)group same amount of powder.
: Quite a few manuals (esp. powder companies) don't list +p pressures. I think +p is still only 58000 psi. I see no reason not to go up to 63000 psi or so-- Winchester 270 is rated @64000 or 65000 psi (I think- I'll look it up when I get home.).

I was wrong on a couple of things. The 270 win max pressure is 62000psi but the 6mm rem (same case is 65000psi). And my velocity for the 117 sst Hornady was 3142fps.
: Barnes max load for the 115X with RL22 is 49grs.

i get that speed from 48.5 gr of rl22.. load from rifle magazine.. accuracy is good but not as good as 43.5gr imr4350 at 2800 fps..which kills really well

A little off topic, but I tried RL25 in my 260 Remington. 50.0 grs. with a 140 gr. Speer Hot Cor, sparked by a CCI 250 Mag primer. 2713 fps avg. for 4 shots. I guessed at the load data too, used H1000 as a guideline. Never shot it for groups though.