Slug guns and ammunition are available in all of the popular guages. The 12 gauge is the most widely used. Most muzzleloaders can only fire one shot, and take too long to reload, but some are accurate to about 125 yards. Many states have muzzleloader seasons, which allow you to extend your time on the field. Hunters can choose between caplocks and flintlocks.
Many hunters prefer flintlocks, but caplocks are less likely to misfire.
Most hunters prefer the .50 or .54 calibers. With muzzleloaders, you have your choice of round balls, conical bullets and pistol bullets. Check with your state laws, many states only allow the round balls for muzzleloading. Handguns, while not always the most accurate and powerful weapons, do present a challenge for hunters. You must be an expert marksman and should realize the limitations of handguns when shooting at deer.