Although muzzleloading rifles may be found in .45-, .54-, and even .36- and .52 calibers, the most common hunting caliber is .50. The “half-inch” bore is the most flexible in terms of loads, has sufficient power potential for commonly hunted game, and offers the widest accessibility of support and maintenance equipment.
A large part of the reason for the change is the development of popular pellets (Pyrodex was first) manufactured in 50-, 30- and 20-grain capsule units.
For whitetail deer hunting, in-lines with a 1-turn-in-24 inches to 1-28 twist will deliver excellent performance with a 100-grain propellant charge and sabots in the 250- to 300-grain range. Conicals in the 300- to 385-grain range typically do very well with a similar powder charge.
A .50-caliber muzzleloader with a 1-32 to 1-38 twist rate should do well with the same sabots and conicals with a propellant charge in the 85- to 90-grain range.
A modern .54-caliber muzzleloader is almost universally manufactured with a 1-48 twist, although I have a still-serviceable 35-year-old side hammer gun in that caliber with a 1-turn-in-72 twist rate, which was good for patched round balls only. An 85- to 100-grain charge will effectively shoot .54-caliber sabots, conicals (try 425-grain bullets) and patched round balls with equal accuracy.
The HK 4.6×30mm cartridge is a PDW cartridge, newly designed by Heckler & Koch for the MP7 and the now-cancelled HK UCP. The 4.6mm round was created as an answer to the 5.7×28mm cartridge developed by Fabrique Nationale de Herstal for their P90 PDW. It was developed especially for a compact, submachine-gun type Personal Defense Weapon, known as HK MP7A1. The cartridge represents a miniaturized rifle round and is loaded with long, pointed bullets to provide adequate effective range (up to 150–200 meters) and good penetration against body armor. There also are other types of loadings in this caliber, such as expanding bullets (for police use) and ball and frangible bullets (for training). So far, only one weapon is produced in numbers to fire this cartridge, the aforementioned HK MP7A1 PDW, which is adopted by German army and British Military Police. Ammunition in this caliber is loaded in Switzerland, Italy and UK. Because of its light weight, the conventional soldier can carry more of the 4.6 mm than for example the 5.56mm NATO (or any other assault rifle cartridge). Also because of its lighter weight, aiming in high rates of fire is easier than other bullets.
Along with the 5.7×28mm, many have claimed these PDW rounds are somewhat ineffective. This claim comes especially from those who disagree with the "energy dump" or "hydrostatic shock" theory of wound ballistics such as Dr. Martin Fackler and Dr. Gary Roberts. Kinetic energy manifests itself in human tissue in temporary stretching of tissue, which most tissue except for liver and neural tissue is able to withstand with little ill effect, and a permanent wound channel. Dr. Fackler and Dr. Roberts claim that the combination of a small permanent wound cavity and frequently insufficient penetration (the FBI recommends a minimum of 30 centimeters (12 in) of penetration in ballistic gelatin) make these PDW cartridges terrible terminal performers. Slow motion videos show that the 4.6 mm bullet yaws at impact on soft tissue. (although this tumbling and yawing is common with many full metal jacketed spitzer shaped bullets). This is because the center of mass of the bullet is behind the geometric center, causing the back to come forward at impact to regain stability, and therefore tumbling through soft tissue, creating a larger wound channel.
