This is the traditional chambering designed to shoot both 5.56 ammo and its civilian variant the .233 Remington. The drawback to this chambering is slight accuracy issues when shooting .233 ammo.
This rifle cartridge developed in the United States for use in the M4 carbine. Its purpose is to achieve ballistics similar to the 7.62×39mm Soviet cartridge in an AR-15 platform while using standard AR-15 magazines at their normal capacity. This cartridge is great for shooting sub-sonic rounds suppressed. It has maximum efficiency when used close up out to 200 meters. Since the 300 Blackout rounds are heaver than a .223 round it makes for a great mid to large game hunting round.
The .223 Wylde is a hybrid .223/5.56 chamber designed by Bill Wylde to yield the accuracy advantages of the match .223 Remington commercial chambering, but without pressure or reliability failures when using high velocity 5.56 NATO spec ammunition. The .223 Wylde achieves better accuracy by having a chamber throat that is tighter than 5.56, but will still function reliably with military 5.56 ammunition because the case dimensions are the same. These facts lead to the .223 Wylde having superior target and varmint accuracy, a compatibility with all .223 and 5.56 NATO ammunitions, and being a top choice for competition shooters.
The .450 Bushmaster is a high-pressure rifle case, thus making efficient use of heavy .452" bullets. Ballistically the round is very flat out to 200 yards. The cartridge fits single-stacked in a standard AR-15 magazine with a single-stack follower. The cartridge in a semi-automatic rifle aims to provide a one-shot kill on big-game animals at 250 yards. States such as Ohio and Michigan allow this straight wall cartridge for hunting of large game.
The 6.5 Grendel is a middle ground between the 5.56×45mm NATO and the 7.62×51mm NATO. It retains greater terminal energy at extended ranges than either of these cartridges due to its higher ballistic coefficient. The 123 gr (8.0 g) 6.5 Grendel has more energy and better armor penetration at 1,000 meters than the larger and heavier 147 gr (9.5 g) M80 7.62 NATO round. This allows a long range rifle to be built on a traditional AR-15 lower, cutting weight and cost over an AR-10 platform build.