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[Review] Aero Precision Upper M4E1 16” 5.56 Mid-Length

The Aero M4E1 complete upper receiver is what I recommend to my friends who want the best bang-for-the-buck.

It’s also the upper that is taking the place of my previous home-defense setup.

Aero Precision Enhanced and M4E1 Uppers
Aero Precision Enhanced and M4E1 Uppers

I’ll walk through everything from fit & feel, to shootability, accuracy, upgrade potential, how it performs in competition, and more. 

Aero M4E1 16" Build
Aero M4E1 16″ Build

Get ready for tons of pics…and a new full YouTube review of the complete upper and Aero lower build kit.

Johnny’s full build is at the bottom of the article!  And if that video helped, please subscribe to our YouTube channel to see the latest weekly uploads.

If you can’t wait…this one with the regular barrel and 12″ M-LOK handguard is the one to get:

Table of Contents


About the Aero M4E1 Upper

The specific upper Aero Precision sent me to test is the M4E1 16” 5.56 Mid-Length Pencil Barrel with their new 12” M-Lok ATLAS handguard.  Pencil means the barrel is thinner…resulting in less weight but reduced stiffness.

But wait…didn’t I say that I recommend getting the regular barrel one?

Aero Lightweight Barrel vs Regular
Aero Lightweight Barrel (front) vs Regular (rear)

Yes…since my previous version of the review showed the awesome accuracy of the regular barrel.  The new handguard PLUS the regular barrel makes the perfect upper.

The M4E1 combines everything I talk about in my AR-15 Buyer’s Guide:

  • 16” barrel so it satisfies all laws regarding length
  • Mid-length gas system for a softer shooting gun
  • Free-floating 12” handrail so you can get better accuracy + a longer grip
  • M-Lok attachment system so you can easily add lights, etc.

Who Is It For?

I’d say the M4E1 is a general use upper.  But especially useful if…

  1. You’re looking for another AR-15 upper that has all the new stuff (mid-length gas, free-floating handrail, and M-Lok)
  2. You’re building a new AR but don’t want to mess with installing the barrel and gas system.  They require tools and I’ve messed up my fair share.  Sometimes you just want a reputable company to build it.
  3. You want the best value upper (or full rifles here).

Fit & Feel

Let’s go through all the parts starting with the “engine” of the gun…the BCG.

2. Aero Precision BCG
Aero Precision BCG

It’s MPI/HPT tested and properly staked…like all my other mil-spec BCG’s that just plain work.  Also correct weight for a full-auto (FA) BCG.

3. BCG Weight
BCG Weight

I got the ambidextrous charging handle which is super beefy and useful if you want to easily brass check (using your right hand on the right side of the handle).  

Ambidextrous Charging Handle
Ambidextrous Charging Handle

Otherwise, it’s probably not worth the extra $60 from the regular one.  The best bang for the buck is still my favorite Bravo Company ($45) one.

Note that the upper doesn’t come with the BCG nor charging handle (sadly this is the norm for uppers now), but Aero’s versions are priced well.

I also got the flip-up sights ($139) which are metal and again…super beefy.  I really like having them on a home defense gun just in case my optic fails.  It’s a little expensive so if you are looking for cheaper backup sights…look at Magpul polymer ones ($60).

Flip Up Sights Weight
Flip Up Sights Weight

Which hopefully it doesn’t since I’m using an Aimpoint red dot.  Check out my recs for the best AR-15 optics.

The rail is machined nicely and has my favorite M-Lok attachment system pioneered by Magpul.  No more quad-rails since that adds unnecessary weight.

Aero Precision M4E1 with ATLAS Handguards
Aero Precision M4E1 with ATLAS Handguards

I also REALLY love the contour for me to place my thumbs where they removed the top middle section of Picatinny.  If you aren’t running tons of stuff on top…it’s a decent weight reduction.

Note…it’s rounded so you won’t be able to stick on a light/laser pad.

And if you use flip up sights and like to place your thumbs on the groove…you’ll have to reverse the rear sight so that it lies down towards the barrel.  Still works fine…just be ready for “hey your front sight is reversed.”

M4E1 with Reversed Front Flip Sights
M4E1 with Reversed Front Flip Sights

If you need/want the full rail on top, there’s now the R-ONE version of the ATLAS.

Aero ATLAS R-One vs S-One
Aero ATLAS R-One vs S-One
at Aero Precision

Prices accurate at time of writing

Prices accurate at time of writing

It’s also thin…about 1.5″ in diameter.  My gripe about the previous generation’s was how thick it was at 2″ in diameter.

7. Aero Side
Aero old gen handguard

The M4E1 comes with a standard flash hider but if you’re going the featureless route or want to really reduce recoil and muzzle rise…I switched mine out for Aero’s VG6 Gamma ($75) muzzle device.

at Brownells

Prices accurate at time of writing

Prices accurate at time of writing

The biggest difference in the new Aero upper receiver is that it gives it a cool billet look without the price increase.  I love the more aggressive lines.

Aero Precision Upper Receiver
Aero Precision Upper Receiver
Aero Precision Upper Receiver, Side
Aero Precision Upper Receiver, Side

Versus a regular upper.

Aero Assembled Upper Receiver
Aero Assembled Upper Receiver

The weight of the old upper with the thicker handguard comes in at 3 lbs 6 oz (without charging handle or BCG) while the new upper with pencil barrel comes in at a flat 3 lbs.

6 oz is a lot of weight that it shed!

But…enough about how it looks.

How Does it Shoot?

After some quick cleaning to get rid of any preservatives or oil, I lubed it up and went to the range.

Aero Precision Upper Review Cleaning

I zeroed in the flip up sights and shot 100 rounds at 100 yard steel.  No malfunctions of any kind.

I’m glad I didn’t have to say to myself…“oh, it just needs a couple hundred rounds to break it in.”

Then came the fun part of taking me out of the equation and shooting groups.

Accuracy: Regular Barrel

Aero M4E1 (Regular Barrel) Shooting Groups
Aero M4E1 (Regular Barrel) Shooting Groups

The results of a 10-round slow string with no cool-down in-between shots with the PMC and my favorite single-stage trigger.

Aero PMC Results
Aero PMC Results

Yes, I messed up one round but it’s roughly 1” (1 MOA).  Which is pretty great for plinking ammo at 100 yards.  

By comparison military XM193 rounds are around 2-3” at 100 yards.

If you look you’ll see the sad face next to Wolf.  I was walking back from the targets and somehow lost the Wolf Shoot-n-C.  I would estimate it was around 2 MOA.  

Accuracy conclusion…I tried to make it the best possible case with a lead sled, a sweet optic, and a crisp trigger.  The rifle holds up so now it’s really down to the shooter.

Accuracy: Pencil Barrel

Pencil barrels have the notoriety that accuracy goes down when it’s heated up from previous shots.  But if you’re looking at shorter engagements or simply “minute of bad guy”…it will do the job.

Aero Precision M4E1 ATLAS Testing
Aero Precision M4E1 ATLAS Testing

I duplicated the original test with the same trigger, sled, and scope.  Here are the results at 100 yards.

Rapid fire meant as soon as I got on target again I shot (around every 2-3 seconds).  While slow fire was waiting for the barrel to be cool and shooting around every 30 seconds.

Aero M4E1 ATLAS 100 Yard, Part 1
Aero M4E1 ATLAS 100 Yard, Part 1

And Part 2 with PMC XTAC (XM193) and Gold Medal (match ammo).

Aero M4E1 ATLAS 100 Yard, Part 2
Aero M4E1 ATLAS 100 Yard, Part 2

So…it wasn’t the greatest.  Here’s my takeaways:

  • Pencil barrel was around 2-3 MOA vs 1 MOA of the original barrel.
  • Visible differences from rapid fire vs slow fire…but not as much as I would have thought.
  • No specific ammo did MUCH better…even the Gold Medal Match.  Looks like you can go with the cheap stuff like Wolf Gold (Best AR-15 Ammo).


I put on my red dot since I wanted to see how fast I could transition between targets at my next competition.

Aero Upper with Aimpoint
Aero Upper with Aimpoint

Recoil and shootability are on par with all the other AR-15’s I’ve shot that aren’t using adjustable gas-blocks.  Which is still…very little due to the small .223 round plus the compensator.

The pencil barrel also did not exhibit extra recoil.


I normally run my lightweight upper but wanted to put the Aero M4E1 upper through the ringer.  

Competitions and me just have a really good track record of breaking down and exposing flaws in guns.


My main problem was choosing to go with the red dot and not getting enough time shooting at long range targets to memorize the drop.


I regularly place in the 50 percentile mark at my local matches and this time was no different.  I re-lubed at the beginning of the match and had no problems.

The Aero feeling at home with other AR-15’s.

Aero at Competition
Aero at Competition

I haven’t competed with the new upper but from a couple hundred rounds at the range engaging 100 yard steel…it’s more than capable even with a red dot.  And much better feeling in the hand with the contour and thinner handguard.

M4E1 with Reversed Front Flip Sights
M4E1 with ATLAS Handguard Setup for Home Defense

Here it is in action in my current home defense form:

Now we’re in the home stretch.


From the Aero site:


  • New enhanced 7075 forging that gives the upper receiver a “billet look”
  • New picatinny profile that blends seamlessly with our Enhanced Series Handguards
  • M4 Feedramps
  • .250 takedown pin holes
  • Laser engraved T-marks
  • Includes port door and forward assist installed


  • Front and rear picatinny rail
  • Eliminated center of top rail for weight reduction
  • Indexing grooves in 12:00 position for positive grip control
  • Quick disconnect sling socket at the 3, 6 and 9 o’clock positions
  • Compatible with low profile gas blocks
  • 1.3” Inside diameter
  • 1.5” Outside diameter


  • 5.56 Nato 16″ Midlength, 1/7 twist, 4150 CrMoV, QPQ, gas port drilled
  • .750 gas block journal
  • Midlength gas system, .0785 gas port
  • M4 Feed Ramp Extension
  • HP and MPI tested
  • Standard A2 flash hider

By the Numbers

Reliability: 5/5

No failures of any kind in the ~1000 rounds of the original and around 500 of the new pencil barrel upper.  But remember to keep it nice and lubed.

Accuracy: 5/5

It’ll do its job with regular plinking ammo.  If you start to reload or use match ammo, you can likely make it a sub-MOA gun if you do your part.  Looks like regular barrel > pencil barrel for accuracy.

Ergonomics: 5/5

Now a 5 with the new ATLAS handguards that are thinner and allow a nice contoured index for my thumb.

Looks: 5/5

Pretty sweet and the details on the receiver make it stand out.

Aero M4E1 with Inforce and Aimpoint
Aero M4E1 with Inforce and Aimpoint

Customization: 5/5

It’s an AR-15 with M-Lok so the sky’s the limit.  Check out my list of the Best AR-15 Upgrades and Best AR-15 Flashlights if you need help.

Bang for the Buck: 5/5

Aero has proven themselves to me as the best bang for the buck in stripped receivers (I have build 6+ uppers on Aero), complete uppers, and full rifles.

Overall Rating: 5/5

Johnny’s Build

Peep the video to see Johnny’s M4E1 in action and check out below to see his complete build list!


The Aero Precision M4E1 AR-15 upper fulfills many roles from plinking to home-defense and has maintained a spotless reliability record. Accuracy, ergonomics, and finish are also great. It’s more expensive than introductory AR-15s but bang-for-the-buck versus “high-end” manufacturers is stellar.

If you’re thinking of getting an AR-15 upper, you can’t go wrong with anything Aero. 

I’ve toured their manufacturing facility in Tacoma, WA and it is legit.  They are a true manufacturer and not just an AR-15 parts assembler.

Aero Precision Uppers
Aero Precision Uppers

My suggestion would be for the regular barrel and the 12″ M-LOK ATLAS handguards.  You’ll get the best of both worlds…accuracy and a kickass grip.

For those of you who want the full rail…there’s the R-ONE version of the ATLAS.

at Aero Precision

Prices accurate at time of writing

Prices accurate at time of writing

Or if you’re looking to shave a 5 oz off and “minute of bad guy” accuracy is enough…the pencil barrel is awesome too.

And if for some reason you’re not feeling it…check out other options in our Best AR-15 Uppers for the Money and Best AR-15 Upgrades articles.

A Few Of Our Personal AR-15 Uppers
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39 Leave a Reply

  • Commenter Avatar

    Hi Eric! Great article! What type of buffer kit does Johnny use in this build? Thanks and keep up the great work!

    October 1, 2021 2:23 pm
  • Commenter Avatar

    Be Very Wary buying from AP nowadays. Their quality is falling off a cliff -- and FAST. I used to love these guys -- multiple builds, multiple builder kits. My last three orders were complete crap. Parts improperly finished and major issues with fit ( >1mm gap upper/lower). I used to buy BLEMs from them because even their blems were high quality. The last BLEM upper/lower I got look like it was dropped in the parking lot and run over by a truck -- on BOTH sides! Sure its functional, but can't be used until its refinished. This isn't the AP we used to know.

    September 4, 2020 6:34 am
  • Commenter Avatar

    I see for that very tight group it says PMC was used. What kind? I looked at the ammo guide. I'm guessing bronze? Thank you. Fantastic read also. You guys do awesome work!

    June 26, 2020 5:58 pm
  • Commenter Avatar
    Cunty McShitterman

    I went with Aero's 14.5" enhanced upper and had a brake pinned/welded. Use as my home defense rifle and for carbine classes. Very happy with it.

    January 4, 2020 3:23 pm
  • Commenter Avatar
    Kennel Tail


    April 24, 2019 2:28 pm
  • Commenter Avatar
    Ken Orlich

    I've done builds with PSA, Anderson, AP and others. I've used AP uppers, lowers, LPKs, etc. The only problem that I've encountered was with the a FDE cerakote upper. BCG wasn't seating consistently in the barrel extension. Yes, I tried different ammo, BCGs, charging handles, stock springs and spacers, barrels and light sanding. All in all, after a few hundred rounds, I think the cerakote was to thick inside the upper because of the amount FDE wear inside the upper.

    April 24, 2019 8:47 am
  • Commenter Avatar

    I've been building a 10.5" "sorta do it all" rifle for home defense, plinking around, and taking some carbine courses.
    My question is: Would you trust your life with this Aero upper? I'm deciding between a 1o.5" aero and an 11.5" Bravo Company. I'd like to save the money on the aero and put that into a titanium BCG. Thoughts? I've been drooling at my keyboard going over different iterations and I could use a 2nd opinion.

    April 29, 2018 3:04 pm
    • Commenter Avatar
      Matthew Collins

      I would pick Aero over almost any manufacturer for a rifle I had to defend my life with.

      April 29, 2018 3:45 pm
    • Commenter Avatar

      I'd take an Aero. BCM is good but IMO overpriced, they don't offer anything over Aero and charge a good bit more normally. I also like the way Aero looks more - not that it matters.

      I wouldn't go with a titanium BCG, nothing wrong with one but unless you want this to be a competition gun there isn't really any gain to it. I'd go with a simple but very strong BCG, like a toolcraft steel BCG. Something wicked strong and heavy - if this is a do it all rifle then Im assuming it is at least in part for SHTF and the value of a heavy BCG that can pound even the crapist of ammo is a major gain. More so than the weight saving of titanium.

      April 29, 2018 5:04 pm
  • Commenter Avatar

    I’ve just bought a 10.5 upper from them. My question is would a cookie cutter muzzle brake fit flush in the free float? Or is it to wide to fit like that?

    April 6, 2018 7:29 am
    • Commenter Avatar

      I've been looking into the exact same build. I don't believe so. the cookie cutter goes out about a quarter inch already. I think a 10.5" handguard from a different company would be ideal, but I'm new at this.

      April 29, 2018 3:07 pm
  • Commenter Avatar

    The M4E1 handguard......does it need it mate up with the M4E1 upper.....or can it be used with any milspec upper?

    March 27, 2018 3:01 pm
    • Commenter Avatar

      It depends, the standard handguards can mount to any standard upper receiver, made by Aero or another manufacturer - but Aero also has an "enhanced" version of their upper and their handguard that uses a different mounting system for the receiver to the handguard. The "enhanced" versions should be mated together to ensure compatibility, however, if you buy directly from Aero there is an option when you get the enhanced handguard for it to include a BAR barrel nut so that you can mount it to a standard receiver.

      If you have an enhanced Aero lower receiver then you need to have an enhanced handguard.

      I don't try to cross them personally, just to make it easy on myself. Standard upper goes with my standard handguard, enhanced upper goes with my enhanced handguard.

      March 28, 2018 5:36 am
  • Commenter Avatar

    Hi Eric, I'm looking to get my first AR in the near future and just trying to learn more. I see Aero has a 15" M-Lok option and curious why you prefer the 12" option?

    February 12, 2018 7:31 pm
    • Commenter Avatar
      Eric Hung

      Good question, Rich...my preferred grip extends out to just under where the 12" handguard ends. 15" would be fine but it would be extra weight in my mind.

      February 13, 2018 9:26 pm
      • Commenter Avatar

        I'm only finding the Aero AC-15 model currently in stock anywhere. This M4E1 cannot be used with that, correct? What would be an option for upgrading the AC-15 later?

        February 17, 2018 11:32 am
        • Commenter Avatar
          Eric Hung

          The M4E1 upper is meant to go on AR-15 lowers. If you get the AC-15 and you want to upgrade, you simply swap out the upper.

          February 20, 2018 11:40 am
  • Commenter Avatar
    Adam Davis

    I was curious I'd the upper itself is mil spec or if it will work on my mil spec lower?

    January 8, 2018 5:50 pm
    • Commenter Avatar
      Eric Hung

      Hi Adam, as far as I know all their uppers/lowers are mil-spec so it should fit on your lower.

      January 12, 2018 5:16 pm
  • Commenter Avatar
    Bobby Joe

    What's the actual length of the 12" handguards. I've seen them reported as 12.5" and 12.65". I haven't been able to get a response from Aero.

    January 7, 2018 5:42 am
  • Commenter Avatar

    Hey, love the "best bang-for-your-buck" content you guys are putting out. Keep it up!

    November 10, 2017 7:08 am
  • Commenter Avatar
    Jon Eller

    Hey Eric quick question. Do you know if an adjustable gas block will fit under the hand guard? Haven't seen one in person so can't quite figure if it will or not..

    November 9, 2017 11:48 am
    • Commenter Avatar
      Eric Hung

      It will if it's low profile.

      November 19, 2017 2:02 pm
  • Commenter Avatar

    JUST bought an Aero (16" Wylde FDE Mlok) yesterday, can't wait for it to arrive.

    May 19, 2017 11:54 am
    • Commenter Avatar
      Eric Hung

      Awesome, let us know how you like it!

      June 5, 2017 12:51 pm
  • Commenter Avatar

    I'm trying to decide between Aero Precision and Core 15. Have you had a chance to review any Core 15 rifles? And further how do Core 15 stack up to your other recommended brands?

    May 6, 2017 4:18 am
    • Commenter Avatar
      Eric Hung

      Hey Zak...haven't had the chance to try out any Core 15 stuff yet!

      June 5, 2017 12:41 pm
    • Commenter Avatar
      Charlie Mason

      I've shot both the Core15 and the .308 version, which I can't remember what they call it? I've shot several Areo's including this upper which I do own. The Core rifles just don't have what the AREO's do in design and basic looks to the rifles. The Prices on Core's are under $400 in some places online. The Core rifles I felt like I was getting less or just right on what I would have paid for had I bought it. The AREO it feels like it's better built & it doesn't leave you feeling like you got a cheap hunk of aluminum in your hands. I'd highly recommend AREO products over Core any day. And question, aren't the Core's built in the Philippines? AREO is built 1/2 hour from me in Tacoma, WA. If you're wanting a good solid rifle go with AREO, if you want to save a few bucks in the beginning, other costs will add up quickly to get better parts that would already be on the AREO. AREO's got the bare bones kits in 5.56 & .308, both are complete minus the furniture and sights some have A2 front sight/gasblock. I have a lot of different builds I've done and have AR Pistols, SBR's, rifles in everything from .22lr, 450 Bushmaster, .233/5.56, 300bo, x39, 6.5 Grendel, .308 & a Noreen Arms 30-06! I like to build them! If you have the time and mechanical aptitude it's easy to build your own. That's the best way to save money. Oh! Radical Arms from Texas has some great builds with smaller prices, check them out too.

      July 3, 2017 3:43 pm
      • Commenter Avatar
        Eric Hung

        Thanks so much for your input Charlie!

        July 4, 2017 10:47 am
      • Commenter Avatar

        I have a Radical Arms 5.56 SOCOM 16” upper paired with a PSA premium NiB BCG and ALG ACT trigger and it jams all the time. The bcg gets stuck in the forward position with a live round in the chamber. Pulling back on the charging handle does nothing, I have to resort to mortaring to free the bcg.
        No matter how I clean and lube it, I could never empty a 10 round mag with it.
        Very frustrating to use and I’ve written Radical Arms but they never responded. Will never buy from them again.
        I hope this aero upper will be different.

        June 3, 2018 9:41 am
  • Commenter Avatar
    Ryan B.

    New AR15 owner here and I just happened to buy an Aero rifle with this upper (Called the Quantum). Choose this over the Saint since I do not want to be a Beta tester for their rifle.

    I was able to buy a Magpul Front and BUS with this and unfortunately, my Front sight does not flip down from not having any room to do so though my BUS does work as intended.

    Despite that, I am happy that I choose an Aero rifle over my list of other models!

    April 15, 2017 3:49 pm
  • Commenter Avatar

    Hi Eric,
    I am looking into buying my first ar-15. I have a military background, Marines, so I'm happy with fixed A2-style front, I'll be shooting iron sights most of the time. This rifle is for self defense with plinking fun gun. I would like to shoot steel ammo, since I'm on a budget.
    Any AR-15 recommendations for me?

    April 14, 2017 6:13 am
    • Commenter Avatar
      Eric Hung

      Hey Jason, have you checked out our AR-15 Buyer's Guide?

      June 5, 2017 12:21 pm
  • Commenter Avatar

    Like the video footage,etc. I'm a budget shooter since now I'm a retired policeman and would like to know what range you use and is it open to Active/Retired Police like yours truly. Currently shoot at Angelus

    Really appreciate your articles.

    March 16, 2017 7:56 pm
    • Commenter Avatar
      Eric Hung

      You're so welcome Sean. I like Angeles and Burro Canyon for the LA region.

      April 5, 2017 4:18 pm
  • Commenter Avatar

    Hey Eric, I've been debating making my home defense firearm featureless in light of some onerous CA registration requirements. I've never tried the J-comp in person but hear it's quite loud. Is that a factor in deciding what HD muzzle device to use? Do you have any other recommendations?

    January 3, 2017 1:28 pm
    • Commenter Avatar
      Eric Hung

      It's pretty loud when you stand next to it since the side vents do a good job reducing felt recoil and muzzle rise. Softer when you're the shooter behind it. But I wouldn't want to be shooting it in the house all the time. For me, the potential hearing loss is an acceptable risk for home defense.

      The 5.56 is loud in general but I can suggest you use comps that project the blast forward so you don't hear it as much, such as the Levang.

      January 4, 2017 9:36 am
  • Commenter Avatar

    Just finished my first AR 15 build, apart from Optic. I went all Aero parts based on your recommendations and further research. The fit and finish are excellent on every piece. No gaps or looseness anywhere. I went with a Builders Kit which came with a 15" Keymod handguard. I have the Nickel Boron BCG and a VG6 Gamma Compensator. Magpul CTR Stock and Aero buffer kit.
    Looking forward to firing it up. Cheers.

    December 30, 2016 5:58 am
    • Commenter Avatar

      Hi Roland, awesome! Let us know how it fires up.

      December 30, 2016 1:43 pm
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