Great find!!! I'm jealous.. I'd love that have that.
I was just talking with Fug about this a week or so ago.
UMC (which Arthur had a relationship with before Savage Repeating Arms) made ammo for SRAC from 1895 to 1897, possibly part of 1898.
Three styles of boxes, I believe..
1) UMC only - no SRACO on headstamp, no mention of Savage on the package.
2) UMC / SRACO - box is labelled UMC, but mentions using Savage Brand of Smokeless Powder and headstamp has UMC / SRACO
3) SRACO - Box is labelled Savage Repeating Arms with either minimal or no mention of UMC. But almost surely had to be made by UMC.
Here's a style 2 box that I had.