There several different types of rifles, but the primary difference in classifying the rifle is based on the size of the projectile the rifle fires and the speed at which the projectile is fired from the rifle.
Pictured are 6 rifle cartridges that all have very different size/speed; all are completely legal in the US, labeled 1-5.
Cartridge #1 is known as a “50-cal round.” The 50-cal round travels 3,000 feet per second and delivers up to 18,000J of energy. The 50-cal round is shot by an “anti-material” rifle. These rifles are primarily used to disable things at long range. For example, the Coast Guard uses 50-cal rounds to shoot outboard boat engines to disable them. These rounds are not practical to shoot back-to-back-to-back in short bursts without the gun being securely mounted due to the massive amount of “kick” produced after each shot. The rifle that shoots the 50-cal round weighs about 30 pounds and is about 5 feet long. Rifles that shoot these rounds are not concealable on a person. These rounds cost about $5/ea
Cartridge #2 is a known as a “magnum rifle round.” The magnum rifle round is shot by a rifle called a “sniper rifle” or “military long range” rifle. Magnum rifle rounds travel about 3,100 feet per second and deliver up to 5,000J of energy. The magnum rifle is primarily used as a long range anti-personnel weapon. For example, a US Army commander would order the use of a Magnum rifle when they need an enemy person +700 yards out to be eliminated by a single shot with a high chance of success. These rounds are not practical to shoot back-to-back to back in short bursts due to the massive amount of “kick” produced after each shot. Rifles that shoot these rounds are not concealable on a person. These rounds cost about $7/ea
Cartridge #3 is known as a “battle rifle round.” The battle rifle round is shot by a rifle called a “battle rifle.” Battle rifle rounds travel about 2,750 feet per second and deliver up to 3,500J of energy. Historically, the battle rifle was primarily used as an anti-personnel weapon for distances between 100 yards and 1,000 yards. Today, the round is primarily used for hunting. The battle rifle round can effectively kill any animal native to North America 500+ yards out. These rounds are not practical to shoot back-to-back-to-back in short bursts without the gun being on some kind of mount due to an intolerable amount of “kick” produced after each shot. Rifles that shoot these rounds are not concealable on a person. These rounds cost about $1/ea
Cartridges labeled #4 are known as “intermediate cartridges.” (AK47 round on the left, AR15 round on the right) The intermediate cartridge round is shot by a rifle called an “assault rifle.” Assault rifle rounds travel about 2,100 feet per second and deliver up to 1,600J of energy. The assault rifle is almost exclusively used as anti-personnel weapon for distances out to about 300 yards. An assault rifle is capable of hunting game up to the size of about a deer, but may require follow-up shots to ensure a quick kill. These rounds produce a very manageable amount of “kick” and can have several back-to-back-to-back shots placed relatively accurately. Rifles that shoot these rounds are concealable on a large person. These rounds cost about $0.75/ea
Cartridge #5 is known as a “plinker round.” The plinker round is shot by a rifle known as a “twenty-two.” The plinker rounds travel about 1,300 feet per second and can deliver up to 200J of energy. The twenty-two is used for target practice and for hunting small game such as squirrel and rabbit. The twenty-two rifle round produces virtually no “kick” and can be shot back-to-back-to-back very smoothly and accurately. Additionally, due to the low amount of recoil, the round can be used in handguns. Rifles (and handguns) that shoot these rounds are concealable on a person. These rounds cost about $0.15/ea