I love the No Excuses 460 grain 50 caliber bullet. He runs them through a die sizer after casting for a consistent fit. They are also prelude. I killed my bull with it last year in Colorado, and will use them again this year in Oregon. They are extremely accurate out of every rifle I have shot the in (like sub MOA in one of my rifles). They are also quite affordable. Order them online:
http://www.muzzleloading-bullets.com
Yes the website looks a bit amateurish, but it's an excellent bullet. I would say probably one of the best if not the best on the market.
Don't use too much powder with a conical, or you will just strip the bullet from the rifling. I tend to get best accuracy around 75-85 grains of powder.
What few guys realize when shooting lead conicals these days is that almost all muzzleloaders have fast twist barrels designed to shoot sabots, and you really need a heavy (400 grain+) bullet for best accuracy in those fast twist barrels.
Also a long heavy bullet extends the lethal range since they retain energy better.