So you’re considering your next (or your first) AR build and you’ve heard a lot of good things about full-size AR rifles. Maybe you want to build yours with a 20 inch AR upper.
Before we even embark on this quest, it’s important to note right out of the gate that there is no “best” upper size. All rifles will perform well under certain circumstances, and some better than others.
Therefore, if you want to know if a 20 inch AR upper is a good choice for you, you need to know what your intended application for that rifle will be.
With that said, here are some of the most practical benefits of a longer barrel.
Improved Stability and Handling
One of the main reasons to build with a 20 inch AR upper is that the rifle itself will be heavier and more stable.
Now, there are some situations in which this would not be a benefit - such as in close quarters, or with respect to maneuverability.
But when long-range shooting or even hunting, the longer barrel and the stability it affords can be seen as a benefit - much as a shotgun with a longer, heavier barrel tends to swing more smoothly than one with a lighter, whippier barrel.
(Potentially) Improved Accuracy
Now, to be clear, the longer the barrel, the whippier it is. Therefore, the shorter the barrel, the more accurate the rifle should be.
But with respect to tuning, it’s probably easier to tune a longer barrel than a shorter barrel. Sure, a longer barrel will whip harder than a short one, but that also means it should be more amenable to the installation of a barrel tuner.
And that means, whether or not the longer barrel is inherently more accurate, once it’s been tuned, it should produce tighter groups.
(Potentially) Improved Accuracy Part 2
While the longer barrel might not engender technically superior accuracy, a 20 inch AR upper will offer a longer sight radius, and that will make it easier for an operator to shoot the rifle more accurately, even if it doesn’t actually make the rifle more accurate.
Sight radius is the distance between the front and rear sights. The longer it is, the more forgiving the sights are, and the less a minor inconsistency will cause issues with point of impact.
It is important to note, however, that this applies only when shooting over iron sights. Nonetheless, the longer the barrel, the more forgiving the rifle will be when shooting over open sights and the easier it will be to shoot accurately.
More Power
Every inch of a rifle’s barrel means there is more volume in the bore to allow the propellant charge to deflagrate, and more linear distance for the bullet to accelerate because it reaches the muzzle and clears the barrel.
Therefore, the longer the barrel, the faster the bullet will be moving when it leaves the muzzle, holding all else equal.
For hunters and long-distance shooters, this is an excellent reason to invest in a longer barrel, as it will produce more power and result in flatter bullet trajectory, which in turn results in a lesser need to hold over a target.
Increased Internal Component Lifespan
You might expect the bore pressures to be higher with a longer barrel, but that is actually not the case. Not only does a longer barrel give the propellant charge more time to deflagrate, in some cases allowing it to deflagrate fully, but it also results in dropping chamber pressures, especially at the point at which the bullet leaves the barrel.
In fact, the chamber and bore pressures of a 20 inch barrel at the point that the bullet leaves the barrel could be less than half of what they’d be with a 10.5 inch barrel.
This results in less port pop and bolt carrier group speed, but it also, importantly, incurs less wear and tear on the rifle’s internal components, notably the bolt carrier group’s locking lugs, gas key, extractor, and the buffer spring.
Therefore, a longer barrel implicates a much smoother operating action (and lower operating pressures) which will generate less wear on internal components, lowering overall maintenance and repair costs over the long term.
Are There Any Reasons Not to Build with 20 Inch AR Upper? (When a Short Upper Is Better)
Despite these glaring advantages of building with a 20 inch AR upper, there are some situations in which a short upper or an SBR or AR15 pistol upper might be better.
Notably, if you’re most concerned with concealment, portability, or handling in cramped quarters, it’s worth it to pass by the advantages of a longer barrel in favor of a short upper.
Regardless, you can explore a wide assortment of 20 inch AR uppers via the previous link. Get in touch with us if you have any questions before starting your project and we will be happy to help.