I have had good luck with Cast Performance Hard cast bullets in my Marlin GG 45-70. They are the most accurate cast bullet I have tried and they are indestructable. If you want to try the heavyweights I recommend a bulletsmith by the name of Jae Bok Young (jbyoungaol.com). His 550gr Crater is the ultimate in 45-70 hard cast bullets. I have handloaded the Crater at approx 1500fps, and if you can handle the recoil it is truly awesome. Good luck.