PPU brass loaded to Hornady specs but with a larger rifle primer? Am I safe?

[Old Bob]

Old Bob,
To fire form the x39 brass, do I go with the starting load or is there a formula to this?

For fire forming x39 brass with 123gr FMJ's I got in bulk from Midway USA (made by Hornady, I think) I used TAC in half my brass & H335 in the other half. I used 25grns of both powders. Depending on which reloading book you look in, these are starting loads or just under starting loads.