When preparing to hunt with a muzzleloader, it is extremely important to choose the right bullet for the job. A good bullet must shoot accurately out of your muzzleloader and offer acceptable terminal performance.
While there are a number of high-quality muzzleloader bullets currently on the market, they are not all created equal and some bullets are better choices than others. Here is how to choose the right muzzleloader bullet for hunting.
The first step is to determine the rifling twist of your muzzleloader. Usually, you may find out this information by looking in the manual. For best accuracy, you must use bullets the rifling in your muzzleloader will stabilize. Generally speaking, when comparing bullets of the same caliber, longer bullets need a faster rifling twist in order to be properly stabilized.
For instance, a muzzleloader with a 1:66″ rifling twist (one full rotation every 66″) is designed for shooting round balls. This is a very slow rifling twist, and it will likely shoot round balls, which are relatively short and light, accurately. However, a muzzleloader with a 1:66″ twist will probably not shoot conical bullets well.

Pictured, from left: 320gr Thompson Center Maxi-Ball, 177gr Round Ball, 350gr Thompson Center Maxi-Hunter.

There is nothing wrong with using a plain, round ball, especially for hunting deer. After all, that is the type of bullet Daniel Boone and Davy Crockett used, and plenty of hunters these days still use round balls in their muzzleloaders with great success. They are also cheap, and you can even make them yourself. However, when comparing them to most modern muzzleloader bullets, round balls are relatively lightweight, have a low ballistic coefficient and offer the least reliable penetration.
That being said, there are some better bullet choices to use for hunting with a muzzleloader. There are two broadly-defined types of conical bullets: full bore conicals and sabots. Though conical bullets typically require a faster rifling twist to properly stabilize, most modern inline muzzleloaders have a 1:28″ rifling twist, which is usually quite good for stabilizing most conical bullets as well as sabots.
There are dozens of full bore conical bullets on the market today. They range from lead conicals, like the Thompson Center Maxi-Hunter and Maxi-Ball (above) to the copper Thor bullets (below left).
Generally speaking, full bore conical bullets tend to be heavier and have a higher ballistic coefficient when compared to a round ball. While the actual accuracy and terminal performance of full bore conical bullets varies, they are generally good choices for hunting.

Pictured, from left: 300gr Thor Bullet, 348gr PowerBelt Copper, 270gr PowerBelt Platinum, 250gr PowerBelt AeroLite, 350gr Hornady FPB.

Another option is to use a sabot (pronounced “say-bo”). This is a bullet smaller than the bore diameter (like a .45 caliber bullet shot from a .50 caliber muzzleloader) that sits in a plastic sleeve (called a sabot) that falls off in flight.
Saboted bullets generally obtain the highest velocities and have the flattest trajectories out of all bullets designed for muzzleloaders. Like with full bore conicals, the accuracy and terminal performance of saboted bullets varies, though they are also generally great choices for hunting.

Pictured, from left: 250gr Hornady SST, 250gr Barnes T-EZ, 250gr Barnes TMZ bullets with and without sabots.

Each muzzleloader is unique, and there are often significant differences between different brands, models and even individual muzzleloaders with regard to which particular load shoots the most accurately.
Because of this, the best way to find out which bullet shoots most accurately out of your muzzleloader is to pick a couple of different brands and bullet weights and test them out at the range. The manual for your muzzleloader can be used as a reference for a few recommended bullets types and weights, but the only way to know for sure is to shoot them yourself.
Finally, before you go hunting, make sure you check the hunting regulations for your state, because they can vary widely. For instance, some states (like California) mandate the use of a lead-free bullet (like the 100 percent copper Barnes bullets). On the other end of the spectrum, Idaho mandates that only lead or lead alloy (no jacketed or saboted) bullets must be used.
Regardless of where you intend to hunt, ensure that you are in compliance with the hunting regulations for that area.