Alternate Caliber ARs

The .223/5.56 NATO cartridge has proven itself on and off the battlefield for decades. Enemy troops have an almost supernatural fear and respect for the AR platform and the deadly ammunition it fires their way. While the .223 may be one of the best multipurpose cartridges out there, it isn’t the best cartridge for absolutely everything. For this reason, AR manufacturers developed their firearms in a wide array of cartridges both larger and smaller than the widely available .223.

6.8mm SPC

Daniel Defense DDV6.8 Mid Length
Daniel Defense DDV6.8 Mid Length

Designers developed the 6.8mm SPC cartridge to address the deficiencies of the terminal performance of the 5.56x45mm NATO cartridge currently in service with the U.S. Armed Forces. The cartridge was the result of the Enhanced Rifle Cartridge program. Participating in the program were U.S. Special Operations soldiers, as well as armorers and other technicians from the United States Army Marksmanship Unit. The development of this cartridge is unusual and interesting in that it was designed by actual shooters in the armed forces, instead of by industry professionals. The goal was to create a cartridge that would bridge the gap between 5.56mm and 7.62x51mm NATO. Daniel Defense built this beauty with a 16-inch cold hammer forged chrome lined heavy barrel with a 1:11-inch right hand twist. The magazine still holds 30 rounds despite the larger caliber. Putting that sweet 6.8 round downrange with this puppy would be more than entertaining!

.243 Remington

ArmaLite AR-10A4
ArmaLite AR-10A4

Sometimes I look at guns and wonder why manufacturers created them to begin with. I admit to thinking the same thing when I saw this one for the first time. What possible advantage could a .243 AR-15 give you over another alternate caliber like the .308? Well, actually, I don’t really know. The .243 is a necked down .308, so you have a very fast and accurate projectile. I suppose recoil would be significantly less than a .308, and the .243 is larger than a .223. It seems to be a decent intermediate cartridge for varmint hunting. Many relatives of mine kill deer with a .243 on a regular basis, so the killing power of the round is not in question. It is probably the smallest round that I would hunt deer with. I’ve heard of many people shooting whitetail with a .223, but I wouldn’t recommend it. For hog hunting down here in Texas, it actually seems pretty useful. Hammering down .243 rounds all night long while ridding my property of those awful critters would be more than exciting. The reduced recoil, compiled with the increased killing power, makes the .243 an interesting choice for an AR cartridge.

.308 Win/7.62 NATO

DPMS Oracle Semi Auto Rifle .308 Win/7.62 NATO
DPMS Oracle Semi Auto Rifle .308 Win/7.62 NATO

If you haven’t fired a .308 out of an AR type rifle, I suggest you try it. It kicks a bit, but that cartridge flies downrange with almost magic accuracy and reliability. The biggest downside to most .308 ARs is magazine capacity. Most of these guns come with a 20 round mag, versus the 30 rounds you get with a .223. A properly configured .308 can hunt most things in North America, while giving you unparalleled performance. There is a reason why most police and military snipers choose the .308 for their sniper rifles. Since its inception in 1952, the .308 Winchester has become the most popular short-action, big-game hunting cartridge worldwide. You can feel confident that thing will bring down almost anything you may encounter on the ranch. I’d like to meet Eugene Stoner, the inventor of the AR platform, and the first guy who had the idea to chamber a AR in .308, and shake his hand. While not ideal for combat due to the decreased ammunition capacity, it is still a hard-hitting, very accurate rifle that is absolutely perfect for varmints, hogs, deer, or any other game you can think of.

.22 Long Rifle

S&W M&P15-22 Standard Semi-Automatic Rifle
S&W M&P15-22 Standard Semi-Automatic Rifle

Practice, practice, practice. That is the key to being an amazing shooter. Shooting a semi-automatic rifle can be an expensive hobby however. Box after box of .223 ammunition can add up, and fast. What is the best way to save money at the range? Easy, shoot .22 LR instead of .223! The M&P15 rifle line has expanded to include the new M&P15-22. Chambered in .22LR, Smith & Wesson built the M&P15-22 rifle with high strength polymer upper and lower receivers. This creates a reduced weight rifle that retains the looks and operating features of the standard M&P rifle. The new M&P15-22 is a dedicated M&P15-format rifle designed and built as a true .22 LR semi-auto from the ground up, with all the standard operating features and accessory specifications of a modern-version centerfire M&P15 rifle. Don’t have anything but cheap lead ammo? This gun doesn’t care. The magazine and receiver will eat any .22 LR ammunition you can throw at it. This is the best choice for shooting all day long, while still being affordable.

9mm Luger

CMMG M4LE9 Semi Auto Rifle 9mm Luger
CMMG M4LE9 Semi Auto Rifle 9mm Luger

What’s that? You want to fire 32 rounds of 9mm out of an AR style rifle? Yea, we can do that. Ammunition for 9mm is relatively inexpensive, while still being an excellent defensive round. Suppression lovers are a fan on this configuration, as well as SBR owners. In my opinion, my favorite thing about these carbines is that I can take one to the indoor pistol range on a rainy day. Recoil on most of these guns in negligible, and tight groups at 50 yards is easy to pull off. Just remember not to tick off your range officer with rapid-firing this little guy. As far as a defensive set up, this makes sense to me. Who would ever want to take in 32 rounds of 9mm hollow point? That would make one big mess. It’s like carrying two Glocks, but with better accuracy and no need to change mags. A proven defensive round out of a proven defensive platform, I’m in!

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (8)

  1. I have several Sig-5566R’s chambered in 7.63×39. I can plink all day on the range (I average 250-500 rounds per visit) at an acceptable cost. The 7.62×39 round, shot from a decently designed rifle like the Sig 556 is very accurate and very deadly at 100-300 yards.

  2. I sure am glad they added the pictures so that I can tell what they look like and will know what one shoots by just looking at it.

    OK, sarcasm aside… why didn’t they at least list the other cartridges that an AR can be adapted to shoot? If they are talking just the common ones, I’ve seen more ads for ARs in 300 AAC, .50 Beowulf and 5.7×28 than I have for the .243 round.

    1. This article has the thoroughness or an elementary school newspaper. I think you are doing the uninformed a great disservice by presenting such a lack of information by leaving out the handful of more common .223 substitutions.

  3. Wish somebody was making an AR styled .410. I have a fairly hard to find Siaga in .410 and it is just awesome with modern defense .410 rounds. The Saiga works fine using the tried and true AK design, but a lighter, quicker handling AR style would be great. The “lowly” .410 in a 3 inch firing (5) 000 buck is impressive. That’s like sending (5) 38 caliber rounds down range with each squeeze of the trigger. Pretty awesome with slugs too.

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  5. Small (.223 size) frame also supports .458SOCOM uppers, which gives the curious combination of the most modern army rifle ergonomics combined with 45-70Govt. ballistics — just the thing for those who feel that small bore can never equal large bore throwing an ounce of lead at a shot.

  6. If you’re wondering who “the first guy who had the idea to chamber a AR in .308” was, it was Eugene Stoner, the designer of the original AR-15, who designed the AR-10, chambered in .308, in the 1950s.

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