Use the round balls, just keep your range under 75 yards, the closer the better. I have a quite a collection of round balls the look a lot like the one in Cayagads post (and I thought I was the only one who kept a revovered round ball in his desk at work). Round balls do the job, just aim for a double lung shot at the longer ranges. Inside of 40 yards you can punch through the shoulder. I shoot 90 grains of FF under .490 RB's and have never had a problem killing deer so long as the range was reasonable and I did my part.

A few years back a buddy dinged a doe in the shoulder with his ML, a .50 Lyman Plains Hunter, shooting round balls. It was a long shot, he thought it was at least 100 yards if not more; he's very good with a gun, he shoots a lot. Long story short, he hit her in the shoulder and she ran off... next day hunting the same area I see a limping doe, I wait till she's about 8 yards from me and drop her on the spot with a spine shot. We found a flattened out round ball in her shoulder and concluded it was his from the day before.

Round balls do the job as long as you are are aware of the range and have good shot placement.