A couple things you can try. 1. Use Semisane's olive oil patch lube (straight olive oil out of the bottle), 2. try some .010" patches, 3. place a felt wad between the charge and PRB, 4. try increasing your charge to 80 gr.
I suspect your patches are burning up because you either have too little lube on them or the patch/ball combo is too tight. It is definately not because your charge is too hot.
Back in the day when PA was PRB only I used to shoot 100 gr of FFFg, .015" patch (Oxyoke prelubed patches) and .490 RB out of my T/C Hawken. And that combo shot very well for me.
When I lubed my own patches, I would melt some bore butter in a shallow tin (a snack pie tin works great) and dip my patches in it, lay them on wax paper, and when they cooled - scraped off the excess BB with a putty knife.