Upper Receiver
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The upper receiver holds the barrel, bolt carrier group and charging handle, and it decides your AR-15's caliber, barrel length and gas system. A stripped upper is the bare receiver; a complete (assembled) upper comes with the barrel and handguard installed, and often the bolt carrier group and charging handle too, ready to pin onto any mil-spec lower. Under federal law the upper isn't the regulated part, so in most places it ships straight to your door.
Filter by barrel length and gas system, compare store prices, and add one to your build to check it against your other parts.
Read our guide: Alternate AR-15 Calibers: 9mm vs 300 Blackout vs 7.62 x 39
Upper Receiver: common questions
Does an AR-15 upper need to go through an FFL?
Under federal law, no: the lower receiver is the regulated part, so uppers usually ship to your home. A few states and cities have their own rules, so check where you live.
Does a complete upper include the bolt carrier group and charging handle?
Not always. Many complete uppers are sold without the BCG and charging handle so you can choose your own; the listing says which. The MyGunLab builder flags a build that's missing either one.
Which caliber should my AR-15 upper be?
5.56 NATO is the most common and the cheapest to shoot. 300 Blackout shines in short barrels and with a suppressor, and 9mm uppers use cheaper pistol ammo but need a matching lower and magazines.
Will a 10.5" or 11.5" upper make my rifle an SBR?
On a rifle with a stock, any barrel under 16 inches makes it a short-barreled rifle, which needs ATF approval first. On a lower set up as a pistol it can stay a pistol, but the rules for braces have changed several times, so check current ATF guidance and your state's law.