I use 70 grains of 2f under a 495 Hornady ball. Deer hit properly will run like their tails are on fire for a few seconds and pile up. If you use the shoulder shot, often you will recover the ball under the hide on the off side. I killed two with roundballs two years back. I did not kill this year. I shot both in the spine to put them down since in both cases I was close to the proerty line. One shot was at about 23 yards, and one at 10. Roundball hunting is not a, "if you can see them" kind of hunt. It is a close range hunt.
Hard cast round balls work just fine if you can get accuracy with them. They are a pain to load, and you have to make your own. They are best left for bigger game than deer.
The only problem with roundball is that the blood trail often does not start for a good ways after the shot. In thick brush, that can be a pain. Luckily, most will go down inside 100 yards if hit right.
Large powder loads with roundball do not create much more damage to the critter, or kill quicker in my experience. In fact, when I used 100 grain 3f loads, I recovered more balls than I do today with 70 grains of 2f. You are aiming to do specific damage to the anmimals system when hunting with roundball. You can not just put a ball in the deer. You have to put a ball in the boiler room or the spine. Me, I don't shoot past about 75 yards with roundball at deer, even tho it is good past that range. I am not 100 percent past that range in hunting conditions, so I don't do it.
Pick a spot. Bigger is better. No blood or hair at the site of the shot is normal, even for pass thrus. The blood trail will be a few yards down the trail, making knowing the last spot you can positively put the animal at more important than the site where he was standing when you shot. If you want a guaranteed bloodtrail, more effective range, more damage to the critter, and all the other things modern guns provide, then you need a modern gun!
The 385 Great Plains HB HP is a very effective deer bullet and is pretty accurate out of every 50 caliber barrel I have ever tried them out of. They are 100 yard deer stompers most of the time. Hit by a truck is a good description a lot of the time using them! Those deer often went just as far as the roundball deer I have killed, but the blood trail was not hard to find!