It really depends on manufacturer of firearm, choice of game, expected range,powder type and load, etc. for instance, I have achieved better grouping at 200 yds using a thompsoon center "mag express sabot" and hornady 240 grain xtp hollowpoint jacketed bullets in .430 diameter over 100 grains of pyrodex pellet in my 209x50 magnum Thompson center encore. Working with the load and bullet, I found the sweet spot after experimenting at the range while keeping within the recommended factory specs. Conical bullets generally will group a whole lot nicer than round ball, and you will find that loose black powder will shoot with more velocity than equal weight of pyrodex, but fouls your barrel more easily. Sabots will give greater muzzle velocity (at least the way I use them) due to decreasing the weight of the bullet. Keep in mind that after a point, your accuracy will decrease when you add more powder charge on a particular bullet. Therefore I shoot three round groups using the same type bullet, keeping copious notes , while increasing the powder charge toward the max recommended load.

I have good sucess with the ones in the sabots.