The upper receiver is where most of an AR-15’s personality lives. Barrel, bolt carrier group, handguard, gas system, all of it hangs off that one piece of aluminum. I’m Lance Rankin, owner and gunsmith at Western Sport in Roanoke, Texas, and I’ve assembled more uppers on my bench than I could count. Here’s how I walk customers through picking one.
Stripped or complete?
A stripped upper is just the receiver itself. No barrel, no BCG, no forward assist, sometimes not even the ejection port door. A complete upper comes assembled, usually with the barrel, handguard, and gas system installed and headspaced by the manufacturer.
If this is your first build, buy complete. I say that as a guy who makes money assembling uppers. A complete upper from a serious maker like Daniel Defense pins onto your lower in about thirty seconds and you know it was put together right. Go stripped when you’ve got specific parts in mind and either the tools to do the work or a gunsmith who’ll do it for you. I torque barrels and check headspace here in the shop every week, so that second option isn’t hypothetical.
If you’re starting from zero on the whole project, my guide to building an AR-15 covers the full rifle, not just the top half.
Flat top or carry handle
Old-style A1 and A2 uppers have a fixed carry handle with the rear sight built in. An A4 flat top gives you a Picatinny rail instead, so you can mount whatever optic you want, or clamp a detachable carry handle on top if you like the retro look.
Unless you’re building a Vietnam or Gulf War clone on purpose, get a flat top. Optics are how people actually shoot now, and a fixed handle locks you out of most of them. If you’re not sure what glass to run, I wrote up my optic picks for home defense that apply pretty broadly.
Barrel length
To be a rifle under federal law, an AR needs a 16-inch barrel and 26 inches overall. Shorter than that and you’re into pistol or NFA territory, which is a different conversation.
For most shooters, 16 inches is the answer. It’s handy, it’s legal everywhere a rifle is legal, and 5.56 still performs well out of it. A 20-inch barrel buys you velocity for longer shots. The 18-inch middle ground mostly makes sense on precision-style builds like an SPR. If you want to go shorter than 16, that’s a whole topic on its own, and my AR pistol guide is the place to start.
Forged, billet, or something else
Nearly every upper worth owning is 7075 aluminum, but how it’s made matters some.
Forged uppers are hammered into shape under pressure, which makes the grain structure dense and strong. They’re the mil-spec standard, they’re light, and they’re the cheapest of the bunch. Hard to argue with.
Billet uppers are machined from a solid block. They cost more and usually weigh a touch more, but the machining allows sharper lines and features you can’t forge, and the receiver-to-receiver fit on a matched billet set is beautiful. I build with billet sets regularly and they make a rifle feel like one piece.
Cast uppers are poured into a mold. They’re the budget option, and honest, they’re the one category I steer people away from for anything beyond a light-duty range gun.
Caliber and compatibility
The upper determines what you shoot. Swap uppers and the same lower can run 5.56, .300 Blackout, .350 Legend, whatever, as long as the bolt and magazine match the cartridge. That’s the quiet superpower of the platform. If you’re weighing 5.56 against .300 Blackout specifically, I compared them here.
Mixing brands between upper and lower almost always works because everyone builds to the same spec, but you’ll occasionally get a little play between receivers. It bothers people more than it affects accuracy. Buying upper and lower from the same maker avoids it entirely.
One legal note: the upper receiver is not the serialized part. The lower is the firearm. You can have an upper shipped straight to your door, no FFL, no background check. Rules can shift, so if you’ve heard otherwise recently, check the current ATF guidance, but that’s how it has stood.
My short version
First AR: complete flat-top upper, 16-inch barrel, forged, 5.56, from a maker with a real reputation. Later builds: that’s where stripped receivers, billet sets, and odd calibers get fun.
We stock complete uppers and parts in the shop, and if you want an upper built to your spec, that’s literally what I do all day. Email [email protected] or call 817-393-4000 and we’ll figure it out.
Lance Rankin is the owner and Chief Gunsmith of Western Sport, a family-run Type 07 FFL and Class 3/SOT dealer in Roanoke, Texas, serving shooters since 2007. Born and raised in Texas with over 50 years of experience handling firearms, Lance purchased Western Sport in 2017 and turned his lifelong passion into his profession. He specializes in AR-15 and AR-10 platform rifles, manufactures Western Sport’s own AR-15 line under the Rankin Industries brand, and runs the shop’s in-house Cerakote coating operation. When he’s not behind the counter or the workbench, you’ll find him on his ranch deep into the night, hunting coyotes with an AR-15 and thermal optics. Lance holds an MBA and personally shoots and tests the products Western Sport sells.
