Short barrel rifles offer a lot of versatility, especially if you intend to build one with an SBR upper, a receiver an an AR15 build kit.
They are shorter and generally lighter than carbines, which makes them potentially better in tight quarters and easier to conceal, but they are free from some of the constraints of AR15 pistols.
Since they are intended to be shouldered, they handle better than ARPs, and the longer barrel offers some serious advantages as well, such as greater accuracy and higher ballistic performance.
Still, that shorter barrel does come with some tradeoffs, and you should pick the cartridge you pair with it wisely.
With that said, here are some of the best calibers for building an SBR.
1. 5.56/223 (Old Reliable)
It’s hard to say what the “best” barrel length for 5.56 or .223 is, and some would tell you that 16” is ideal because it offers enough length for the propellant charge to fully deflagrate while still offering solid accuracy and muzzle velocity.
It is also the case that a longer barrel will be heavier and therefore more stable, and will offer a higher muzzle velocity and therefore a slightly flatter trajectory, which is better for long-range shooting.
On the flipside, ARPs, though they are often chambered in 5.56 or .223, really don’t offer the best barrel length because the propellant charge won’t fully burn up before the bullet leaves the muzzle. As a result, ARPs chambered in 5.56 or .223 are loud and messy, with a lot of muzzle pop.
That leaves SBRs, with barrel lengths in the middle ground between ARP and carbine territory. They offer solid performance, all things considered, and since both these cartridges are cheap, relatively available, and accurate, they represent a solid choice for building with an SBR upper.
One note for those of you that can’t choose between 5.56 or .223 and want the flexibility to shoot both, get a short barrel upper with a .223 Wylde chambering, a hybrid chamber that can shoot both of these cartridges.
2. .300 BLK
For those looking for a cartridge that offers superior stopping power up close than 5.56 or .223, but which is overall a very similar cartridge in terms of size and dimensions, go with .300 BLK.
One of the main selling points of .300 BLK is that the parent case is .223, and therefore it can be used with most 5.56/.223 AR parts.
However, it is also the case that .300 BLK hits harder at close ranges than 5.56 or .223, offering superior firepower. It also performs much better from a shorter barrel, giving it a clear edge if you intend to build with a short barrel upper.
There are some caveats here. It is hard to find and expensive, so be aware of that. It might be worth your while to get into handloading if you want to build a rifle chambered in .300 BLK.
Another is that it delivers abysmal performance between 200 or so yards. This is not a long-range cartridge by any means.
3. 7.62x39mm
The 7.62x39mm, AKA the 7.62 Soviet, is the perfect low-cost, high-availability alternative to .300 BLK. In many ways they are very similar, given the fact that they are both in the 7.62 class.
Both perform well from short barrels, both offer higher stopping power up close than 5.56 or .223, and both do not perform well at longer ranges.
This makes the 7.62x39mm an excellent alternative to 5.56 or .223, but on top of that, it is also a great alternative to .300 BLK because it is cheap and widely available, whereas the latter is expensive and hard to find.
4. 9mm
This list of short barrel upper appropriate calibers wouldn’t be complete without at least one nod to a handgun cartridge, and the 9mm it is.
The humble but effective 9mm is affordable, widely available, and highly effective as a defensive cartridge, especially at close ranges, which makes it perfect for a pistol-caliber SBR. It also performs well from short barrels, being a handgun cartridge, which makes it great for pairing with an SBR build.
If you need good up-close performance at a relatively low price point, and aren’t opposed to a pistol-caliber SBR upper, then seriously consider 9mm because it is a solid alternative to the rifle calibers listed here.
Explore SBR Uppers and Parts Here
These are only 4 of your potential options for building with a short barrel upper, but they are definitely among the best, though that is not to suggest that there aren’t others. Check out our full collection of short barrel uppers here and if you have questions about performance, parts, compatibility, or the project itself, get in touch with us.