A whole lot is going to depend on the diameter of the bullet as-cast versus the bore size. As with patching an RB, you're going to need to adjust patch thickness to bring about the right relationship between the two.
I've not tried in a ML, but have shot paper patched pure lead bullets quite a bit in my BP cartridge rifle (50-140). Results were so-so, probably due to faults in my patching technique and a little difficulty I encountered in getting patch thickness to come out just right with the paper I was using. I had outstanding results with paperpatch bullets made by a friend, and would probably use the same methods he did if I pursued it further. After patching his bullets, he pushed them through a sizing die to smooth and true things up. I have no clue whether that would make a difference patching a conical for a ML, but it sure brought out the best in my Sharpes.