Does anyone know where one can buy "new" .257 Roberts Ackley Improved brass? I'd pay a premium for once fired brass to use in one of my rifles. MMP

Not sure I ever seen 257 AI brass new. I'd suggest getting some Winchester 257 +p brass and fire form in you own gun.

By all means, load and fireform your own brass from virgin .257 Roberts. Use full power loads. In all the fireforming I've done with improved chambers, the fireforming loads were virtually equal in accuracy to those made with fireformed brass. Only the velocity was lower, and then only marginally.

Even if you were able to find fireformed brass from another chamber, chances are it would fit your chamber poorly, making you no better off than with unfired brass.

BTW, the "+P" on the headstamp is only to identify the factory loads as exceeding SAAMI pressures for the standard Roberts. There is no difference in Roberts brass with or without this symbol.

I own a 257 Bob AI

+1 for what Stonecreek says, use my fire-forming loads for target practice; but if you think that is a waste of bullets & powder, do a search on "fire forming" and you will see it can be done with a lighter load & a media like Cream of Wheat; no bullet & you can do it in your back yard, if your wife doesn't object to the mess

Do you get enough improvment out of you 257 AI to suggest doing it to a new Kimber M84, or would you just shoot it like it is. I obviously haven't read the data on them yet, but have given it some thought. Did you convert a 257 Roberts, or did you build yours from a different caliber?

I bought a Win M-70 that was already converted

I'm not sure I really needed the AI but I was looking for a Dall sheep rifle & it sounded cool; honestly, not sure I would do it again unless I was using going to use it manly for sheep, speed goats or Mules in wide open country; IMHO, not necessary for most whitetail hunting

Positive side is you can still shoot 257 Bob loads off the shelf and they work just fine

The 257 AI is a "wildcat", and one of the better ones too. By definition, that means there is no factory ammo or cases made for it.