Do Aero lowers fit Radical Firearms uppers?
Aero lower + Radical upper: yes, they fit
Yes. Aero Precision AR-15 lowers fit Radical Firearms AR-15 uppers. Both are AR-15 size receivers. A real mil-spec keeps AR-15 receivers from different makers close, though not exact, and fit problems show up most when the upper and lower come from different makers. We checked them with the rules the AR builder runs.
Fit comes from the same rules the AR builder runs on every part you add. Build data only ranks the setups; it never decides fit. Checked October 31, 2026.
Our take
Most built setup: the Aero M4E1 lower with the Radical 5.56 Barreled Upper.
About 1 in 30 Aero lowers in our builds carries a Radical upper.
Aero makes forged AR receivers, mainly the M4E1 line, with a billet look that still takes standard mil-spec parts. They also make complete uppers, charging handles and rifles.
Founded 1994, Tacoma, Washington, Made in USA
Radical Firearms makes low cost complete uppers, lowers and rifles in Stafford, Texas. They machine the guns themselves instead of assembling bought parts.
Founded 2012, Stafford, Texas, Made in USA
Aero lowers and Radical Firearms uppers by platform
Each row is checked on the most built part of that platform from each brand.
| Platform | Fit |
|---|---|
| AR-15 | Yes, they fit |
AR-15: yes, they fit
Both are AR-15 size receivers. An AR-15 lower takes the upper's 5.56 NATO.
Checked on this Aero lower
Aero Precision M4E1 Lower Receiver W/MOE SL Grip & SL-S$233.99, out of stockand this Radical Firearms upper
Radical Firearms 5.56 Socom Upper$399.99Most built Aero lowers and Radical Firearms uppers setups
Ranked by how often builders pick the exact pair. Only pairs our rules pass are listed.
#1Yes, they fit29% of these buildsCheck fit
#2Yes, they fit16% of these buildsCheck fit
#3Yes, they fit8% of these buildsCheck fit
#4Yes, they fit7% of these buildsCheck fit
#5Yes, they fit6% of these buildsCheck fit
#6Yes, they fit6% of these buildsCheck fit
#7Yes, they fit3% of these buildsCheck fit
#8Yes, they fit3% of these buildsCheck fit
What Aero and Radical Firearms say
Aero Precision: The M4E1 upper is forged 7075-T6 with a billet style look, and it still takes a standard barrel nut and mil-spec parts.
Aero Precision: The rear takedown pin detent hole on Aero's Gen 2 AR15 lower is threaded for a 4-40 set screw.
Aero Precision: Aero's Gen 2 AR15 lower is machined to mil-spec dimensions, works with standard AR15 parts and magazines, and has a nylon tipped tension screw for a tight fit with any standard AR15 upper.
Radical Firearms: Radical's 5.56 SOCOM complete upper is ready to attach to any mil-spec lower and comes with a bolt carrier group and charging handle.
Radical Firearms: Radical's 5.56 and 300 Blackout uppers run standard 5.56 mags, and 300 Blackout uses the same bolt carrier group as 5.56.
Radical Firearms: Radical's 6.5 Grendel, 7.62x39 and .450 Bushmaster uppers need caliber specific mags, and 20 round mags are recommended for 7.62x39.
Fit is judged from the specs retailers list, which can be missing or wrong. Confirm with the manufacturer before you buy, and have a qualified gunsmith check any build before you fire it.
Other uppers builders put on Aero lowers
- Aero lowers + Aero uppersMost picked
- Aero lowers + BCM uppersSecond most picked
- Aero lowers + Geissele uppersThird most picked
- Aero lowers + Wilson Combat uppersFourth most picked
- Aero lowers + PSA uppersFifth most picked
- Aero lowers + Daniel Defense uppersSixth most picked
- Aero lowers + YHM uppersEighth most picked
- Aero lowers + TacFire uppersNinth most picked
Other lowers under Radical Firearms uppers
- PSA lowers + Radical uppersMost picked
Aero lowers and Radical Firearms uppers: questions builders ask
Will a Radical upper fit an Aero lower?
Yes. Aero AR-15 lowers fit Radical AR-15 uppers. Both are AR-15 size receivers.
Do I need a matched upper and lower?
A real mil-spec keeps AR-15 receivers from different makers close, though not exact, and fit problems show up most when the upper and lower come from different makers.
Why might a Radical upper feel loose or tight on an Aero lower?
Some play between an AR-15 upper and lower is common, but it can get excessive when the two come from different makers, and a tension screw or an Accu-Wedge takes it up.