The AR-15 platform can fire very different cartridges, but each needs the right parts. Mixing them up is a safety problem, not just a performance one.

The .223 and 5.56

The .223 Remington is what most AR-15s were built for. SinterFire's frangible loads, at sinterfire 223 ammo, are a specialty variation, made to break up on impact, which is why they are chosen for steel targets and close-quarters training.

A rifle marked 5.56 NATO accepts both the .223 Remington and the 5.56. One marked only .223 Remington should be fed .223 loads, because the military cartridge runs at higher pressure.

The 224 Valkyrie

The 224 Valkyrie uses a case that needs its own barrel, bolt and magazines, even though it fits an ordinary AR-15 lower. It was designed to deliver long-range performance with heavy .224 bullets, and its loads are at 224 valkyrie ammo for sale.

The 300 Blackout

The 300 Blackout is a .223 case necked up to .30 caliber, so it uses standard AR-15 magazines and bolts and needs only a new barrel. That convenience is also the risk: a 300 Blackout cartridge can be loaded into a 5.56 rifle by mistake. Anyone who wants to buy 300 blackout ammo should mark the magazines clearly.

What each swap needs

In short, the .223 needs nothing extra, the 300 Blackout needs a barrel, and the 224 Valkyrie needs a barrel, a bolt and magazines. A change of cartridge is a change of parts, not just a change of box.

The larger AR-10 platform

Larger AR-style rifles are built around the .308 Winchester case and its relatives, and two cartridges in this series fit that platform. The .243 Winchester, a necked-down .308, has loads at 243 ammo. The .308 itself has polymer-tip loads at 308 polymer tip ammo.

Bolt-action cousins

The rest of the series belongs mostly to bolt-action rifles. The .270, with 150-grain loads at 270 150 grain ammo, is a classic deer-and-elk cartridge. The .280 Ackley Improved, with polymer-tip loads at 280ai polymer tip ammo, is a sharper-shouldered cousin of the .280 Remington.

The magnums are the long-range hunting cartridges. Nosler's 300 Winchester Magnum loads are at nosler 300 win mag ammo. Its short-action cousin, the 300 WSM, has loads at 300 wsm ammunition.

The .303 British, with 180-grain loads at 303 british 180 grain ammo, is an old military round found mostly in Lee-Enfield rifles.

Mixing AR-style cartridges is dangerous. Never put a cartridge in a rifle that is not marked for it, and confirm current stock and state shipping restrictions before ordering.