I've had good results in my TC Hawken 1/48 .50cal with 70 gr Alliant Black MZ. I tried several heavy conicals including just casting my own. My best was my own a .503 450 hollow base. I have a White Bison. 504 I was having trouble with and got a tip to put a wad between the powder and bullet. That worked better. No Excuses bullets has a test kit of a new 420, 460, and I think a 495 in an assortment of sizes from .500 to .504. Or you can just get the 420s in .502. On my Hawken I size down to .502.
before casting my own there us a guy out of Iowa on Gunbroker.com that sells a variety of conicals. He has a 435gr .503 hollow base that I had good results with. It's like 96 bullets for around $40. I'm not at home rt now but I can review my stock and can see some of my stock and create you a test pack. You can pay shipping and a modest fee for the sample if interested. I will include some wads. I lIke Black MZ but you can use anything but 209 and should be ok. One other option is I've read good things about Bullshop bulltes. Never tried them but never read any negatives. This was already stated, each gun has its own best bullet/powder combo. You just have to figure it out. Personally with heavy conicals I m staying around 70 grains. Those brass butt Hawkens kick like a mule.