Considering another home build for your collection, or perhaps your first? One of the great things about modern sporting rifles like the AR-15 is that there is a great deal of variety in cartridge pairings.
Nowadays, you don’t need to settle for a complete 5.56 AR15 upper receiver. You still can, but that choice is yours and there are a lot of other options out there.
So, with that said, let’s unpack some of the top AR calibers for you to consider before you start your next build.
.223/.556 AR15 Uppers
The 5.56x45mm NATO has long reigned supreme in the realm of AR chamberings, and for all intents and purposes we’re going to lump .223 Remington in here with it.
The 5.56 has a lot going for it. For one, it is extremely widely available and as far as cost, it’s the most affordable caliber, per round, on this list. Since it is so affordable, it is a top choice for high-volume target shooting, plinking, and training.
Both 5.56 and .223, which produce basically the same performance, generate almost no felt recoil, so most shooters can shoot them all day long. They are also excellent long-range cartridges, one of the best ones on this list (the other being 6.5 Grendel).
Also, 5.56 and .223 are excellent for small and medium game, up to coyotes. In fact, many consider these the ultimate cartridges for varmint and predator control.
They’re also light and small, so you can carry a lot of them all day, without fatigue. This is good for hunters and competitive shooters.
So now, what’s not the best about them? Well, it pretty much comes down to stopping power. Of all the cartridges on this list, these produce the least, so if stopping power matters, you might want to consider a different one.
Honorable mention: if you like both the .223 and 5.56 and want the flexibility to shoot both, build a rifle with a .223 Wylde AR15 upper. This is a hybrid chamber, not a cartridge, but it can safely fire both .223 Remington and 5.56x45mm NATO, so you don’t have to choose between the two.
.300 Blackout Uppers
This cartridge was actually developed using the .223/5.56 as a template, so that AR aficionados could shoot a .30 caliber class cartridge without making serious changes to their platform.
In fact, ARs chambered in .300 Blackout can use the same lowers and magazines. They even use the same bolt. You just need a new barrel - but if you’re not comfortable with that, just start with a .300 Blackout upper.
This cartridge fires a heavier bullet and produces a lot more stopping power at close range than either of the former. It has a badly drooping trajectory, but within 100 yards, the .300 BLK takes the cake when it comes to power.
Also, it’s relatively affordable and fairly widely available, and generates only a little more felt recoil than 5.56 or .223. You can even repurpose old 5.56/.223 rounds and reload them as .300 BLK, so there’s that.
Basically, if you like a standard AR15 but want to shoot a heavier bullet without making serious chambering adjustments, consider a build with a .300 Blackout upper.
.350 Legend Uppers
The .350 Legend was developed for basically one purpose and one purpose only. To give AR shooters the ability to hunt in areas where only straight-walled cartridges are legal.
Here’s the thing about .350 Legend. It doesn’t have the same ballistic performance as the bottlenecked cartridges on this list, but it is a straight-walled cartridge, so if you hunt deer in states like Ohio or Indiana, which have bottlenecked cartridge restrictions, it’s one of the better ones on this list.
Just be aware, .350 Legend isn’t produced by a lot of ammo manufacturers and it’s sort of a niche cartridge, so expect to pay more for it, and it might be hard to find in some places.
But for what it was designed for, it’s a pretty solid option.
6.5 Grendel Uppers
For long-range shooters that need performance at the end of the day - such as for hunting - and need a cartridge that is better than either 5.56 or .223, but not as heavy or specialized as .308 or 6.5 Creedmoor, the 6.5 Grendel is your ticket.
Don’t take that to mean something it doesn’t. The .308 is still a more powerful cartridge, even at longer ranges, but if you’re looking for a lighter cartridge that can still dispatch medium game (like whitetails) at intermediate ranges, between 400 and 600 yards, then the 6.5 Grendel is a great option and you shouldn’t overlook it.
7.62x39 Uppers
Last but not least we have the 7.62.x39 - otherwise known as the 7.62 Soviet. This is the cartridge that was infamously paired with both the AK-47 and SKS families of rifles.
Do not mistake this with either .308 or 7.62x51mm NATO. They are not the same cartridge although they are the same caliber.
Rather, the 7.62 Soviet lies between the two. It offers substantially more power, especially within 100 yards, than the 5.56 and .223, without quite reaching the power of the .308. Also, it’s not a good long-term cartridge. Beyond 100 yards, it’s spotty at best.
But, there is a good reason (besides nostalgia) to build an AR-style rifle with a 7.62 Soviet AR15 upper, and that’s because it offers similar performance to .300 BLK at a (potentially) lower price point.
The .300 BLK can be an expensive cartridge to shoot, whereas, due to a large volume of surplus ammo on the market, there is a lot of 7.62x39mm out there. Just be careful when shooting old, surplus ammo, as it can be corrosive.
Basically, if you’re looking to build an AR-style rifle around an affordable cartridge that performs better at close range than 5.56 and .223 do, consider the 7.62x39mm.
Start with an AR15 Upper from MCS Gearup
Good news - if you’re interested in building a rifle with an AR15 upper in any of these chamberings, we have it, and others.
Take a look through our collection of uppers, lowers, parts, and AR15 build kits, and if you have any questions before you buy, get in touch with us at Sales@MCSGearup.com