I don't know about a max load but this one might get it done.

My BFR in 500JRH has a 6" barrel and with 31.0 grains of Lil'Gun behind a 440 grain cast with 90* metplate does 1,428fps on average (SD 23)with a rifle primer (CCI BR-2). No signs of pressure in my revolver but it does knock hell out of my trigger finger.

Didn't touch one off with a WLP with Lil'Gun but from my testing the rifle primer gave on average 25/35fps more velocity using H110 over the WLP. I don't use the CCI-350 jus cus. I seriously doubt you'll get much of a pressure spike from that CCI rifle primer over that caused by the CCI-350, which is the hottest pistol primer on the market IMO.

The 90* cast came from Ranger Rick, who no longer is in the business of selling cast bullets.