I have had to buy any powder I can locally. I have some rl-15 and rl-17 but cannot find any use for it in my 375 jdj. Anybody have any experince with these two powders.

I found a pound of imr4064 and loaded some 45-70 government ammo wit it for my contender. There is no data for this in a contender so I used data for trapdoor rifles. I'm starting with a charge of 47 grains under a 300 grain bullet. What is your opinion of this load

Cast or jacketed? The load seems pretty light according to my books.

My Speer#13 gives 51 to 55 gr imr 4064 and a 350 gr bullet for the trapdoor, no 300gr bullit listed. Your 47 gr load is a bit light. I use rl-7 and 300 gr bullets with trapdoor loads in my 12 in, its a hammer on deer.
According to the Hornady 5th edition you can use imr 4064 in the 375 jdj with the 270 gr sp 44.3-1700fps 46.2-1800fps 48.2-1900and 49.2 max-1950fps

I went to range and tried the imr4064 with 270 grain bullets. It was not fun. I do not if it was the different powder, heavier bullets, or wet hands but my thumb took a beating. The gun kept rotating in my hand and hammer extension would hit my thumb. I tried three shots and gave up. I will try again when it's not raining.

I picked up some Reloder 17 earlier this year and decided to try it in the 309 JDJ. I started with the lower range of loads for IMR 4350 with both 150 and 165 grain bullets and worked up in 1/2 grain increments (with a chronograph), and thus far the Reloder 17 is working quite well. This quote is from the Alliant web site on Reloader 17: "Similar burn speed to IMR 4350 with added velocity."

Hodgdon's shows 49.8 to 53.0 for cast and 57 to 60.5 for jacketed. Levergun load is 59.0 to 65.5C for 300 Sierra JHP