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Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper

Increase Your Odds of Survival When Getting Out of Dodge

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper

If you need a small firearm that can also perform like a rifle at distances of 100 yards, the Aero Precision’s M4E1 7.5-inch Atlas S-One upper assembly may be just what you are looking for with your AR-pistol build.

The first semi-auto rifle-caliber handgun I ever remember seeing was a Bushmaster Arm Pistol sometime in the late 1970s. This was the commercial version of the IMP survival gun designed for the USAF to store under a jet pilot’s ejection seat. There were two main versions of this firearm, one with a top charging handle and safety located in the trigger guard (known as the Gwinn model,) and another with a side charging handle and AR-15-type safety in the rear of the receiver; both models utilized AR-15 and M16 fire-control parts and both were of a bullpup design. Designed to lay across the forearm, it was more of a point-and-shoot firearm than an aim-and-shoot one. Is this unusual? Not really, as point shooting was still a thing at the time, an important skill which seems to have been lost these days. Was it accurate? Depends on the situation. If you placed it on a shooting bench and took your time, you could hit a full-body silhouette target at 50 yards (much of the time), but don’t be expecting tight groups. I finally got one in 1998, and sold it about 10 years later. Today, I wish I hadn’t, but then again, I’m also a gun collector. (For a detailed look at this firearm, be sure to pick up issue #13 on sale July 6, 2021, which is our annual Retro Guns issue. There will also be a video demo on our website at

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
The Bushmaster Arm Pistol as it appeared in the 1982 Guns & Ammo Annual catalog section.

It wasn’t until the early 1990s that a commercial AR-15-type pistol appeared in the form of Olympic Arms’ OA-93. This was a short-bolt designed AR-15 pistol which did not incorporate a buffer tube. Models began appearing with standard-length buffer tubes, and since these were less expensive than the Olympic Arms version, they began to take notice. Then, the 1994 domestic “assault weapons” ban was passed, which banned future production due to the law specifying a maximum handgun weight along with the usual “assault weapon” traits, so the design lost its traction. Olympic Arms skeletonized its gun to shed enough weight that production resumed, but this model just didn’t have the spark of the original, as it was expensive and looked like a sieve. Later, a company named Professional Ordnance came out with its Carbon-15 line of AR-style firearms, and its pistol version was light enough to avoid the ban, as it utilized carbon fiber extensively. Some at the time considered these AR handguns as just “fun guns” with no real utility. However, many of us not only saw real uses for these large AR handguns, but also were impressed with their performance at distances out to 150+ yards. The ability to have a semi-auto rifle-caliber handgun (many as short as 16 inches) to defend yourself from multiple attackers, shoot through the bad guy’s protective barriers, take down a deer, and which was small enough to easily drop into a medium-sized bug-out pack, was very attractive to survivalists, or even the home owner. The Rodney King riots in Los Angeles also influenced many of us to look for alternative firepower.

I have owned and reviewed AR-15-type handguns over the years, but all had barrels at the 10.5-inch mark. I like this length, as the velocity and accuracy is good at 200 yards, but sometimes I felt that the overall length was just a bit too long for some situations, especially when moving around in a vehicle, storing it in a small pack, or concealing it under a coat. I just wanted to go a little shorter. My concern was the loss of accuracy and velocity, but then again, if I’m moving toward the shorter 7.5-inch barrel for a compact AR-style SHTF gun, I’m not looking to shoot a soup can at 300 yards, I’m looking at hitting a bad guy at 100 yards and killing a small- to medium-sized deer at 50 or less. The difference in velocity between a 10.5-inch barrel and a 7.5-inch barrel can vary from a 200 fps to 500 fps loss, at the muzzle, depending on bullet weight. However, this shorter barrel will be sailing a 5.56 bullet that is definitely still more than deadly at 100+ yards. My second concern was muzzle blast. Before I get into accuracy and muzzle blast issues, let’s take a look at the upper I chose for the job.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
For comparison of length, here are three AR-15-type firearms: a lightweight AR-15 carbine with 16-inch barrel (TOP), 10.5-inch barreled AR-15 pistol (MIDDLE), and the Aero Precision M4E1 Atlas S-One with 7.5-inch barrel (BOTTOM).

I had no qualms about going with Aero Precision, and I became familiar with its high-quality barrels while working for Beretta about a decade ago, as Aero submitted barrel samples for a manufacturing project. Having owned AR-15s since 1978, I have seen hundreds of manufacturers’ AR-15 parts as well as completed rifles - Aero Precision is one of the highest quality manufacturers out there, so I ordered its M4E1 7.5-inch complete upper in 5.56 with the Atlas S-One barrel shroud. Now, some of you may be thinking: “Why not get the upper in .300 Blackout (BLK), as that would be a better deer killer and man stopper?” My answer is ammunition availability. This is a survival gun for a small pack that I may be traveling with by car or by air. The chances of me finding additional .300 BLK are going to be a lot less than finding .223 or 5.56, especially in the ammunition apocalypse we are in now. Many gun owners have stockpiled .223 and 5.56 for decades when prices were low, I even have a bit of .223 ammo from 40 years ago. I don’t know if I would be successful finding and buying, or bartering for, any 5.56 far from home, but at least I know that this caliber is out there. Now for a closer look at the upper.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Aero Precision M4E1 Atlas S-One upper assembly as sold.
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper

The Aero Precision M4E1 Atlas S-One upper assembly has a ½”x28 threaded CMV barrel at 7.5 inches. CMV, or Chrome-Moly Vanadium, is a military spec 4150 steel that also contains vanadium, which greatly increases the strength of the barrel as well as the high-temperature rating and stability of this material. This high-quality is not always seen in typical AR-15 barrels. The twist rate is one turn in seven inches, which is great for this length barrel and for many 5.56 bullet weights. The barrel also incorporates M4 feed ramps, M4 barrel extension, .75 gas block, and is chambered appropriately in 5.56x45mm. The free-float barrel shroud incorporates front and rear top Picatinny rails, multiple M-LOK positions, quick disconnect sling sockets, and weighs only 4.9 ounces with only a 1.5-inch outside diameter. Most parts have a QPQ corrosion-resistant finish. It also comes with the forward assist and ejection port cover installed – complete bolt carrier and charging handle sold separately.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
The free-float barrel shroud incorporates front and rear top Picatinny rails, multiple M-LOK positions, quick-disconnect sling sockets, and weighs only 4.9 ounces with only a 1.5-inch outside diameter.

I decided to park this high-quality upper assembly on an Aero Precision lower receiver, even though I initially was going to incorporate an 80% polymer lower build into this article. As I planned the build, I changed my initial idea of just using standard AR-15 parts and instead chose some upgrade enhancements. First, I contacted Midwest Industries and obtained one of its Enhanced AR-15 Drop-In Curved Triggers (#MI-TRIGGER-C) which is set at 3.5 pounds – I was VERY excited to try this out.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
An Aero Precision lower receiver was chosen for the build. Hey, why not make everything match?
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Midwest Industries’ Enhanced AR-15 Drop-In Curved Trigger was chosen for the build. A 3.5-pound pull!
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Bottom view of the Aero receiver shows a skeletonized trigger guard, which is much more solid than the standard G.I. foldable trigger guard.

My second upgrade was a KynSHOT hydraulic recoil buffer from KYNTEC Corporation. I have been building AR-15s since around 1981, and my first job in the industry was building them in 1982. I have seen a ton of buffers over the years, from 1.5-ounce carbine buffers (with no weights) to the vintage/retro Edgewater buffers, but I haven’t ever tried a hydraulic buffer. Heard about them, but never tried one, so I was also excited to give this a test.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
A standard 3.5-ounce AR-15 carbine buffer (LEFT) in comparison to the high-tech hydraulic buffer from KYNTEC Corporation.

I have used the foldable AR grip by FAB Defense for years, and it is my pick for any bug-out AR-15-type firearm to make it more storable – it went into the build. As far as the buffer tube, I just wanted to keep this as simple and with the smallest footprint as possible and only added a short pistol buffer tube with foam padding.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Foldable AR grip by FAB Defense is great to store emergency supplies like spare parts or survival items like a G.I.-type can opener, micro fishing kit, butane lighter, or even a 5.56 to .22LR conversion chamber adapter kit from MCA Sports.

For my optic, I used one of my favorites, which is an Aimpoint Micro H-2. I sometimes have issues with dot optics due to an astigmatism, but this optic works just great for me. As far as back-up sights, I did something a little different. I chose some lightweight polymer sights from Mission First Tactical (MFT), removed the rifle peep sight from the rear assembly (SKU: BUPSWR), and replaced it with the CSAT rear AR-15 sight from XS Sights, but not in its original condition (NOTE: Sight retaining bolt must also be replaced for the correct thread pitch). Since this is a handgun, I would much rather use a notch sight than a peep sight. The CSAT has two sights which are connected in flip style. One is a peep with a large aperture, and the second is a small aperture with a notch sight on top. I removed the large aperture with a Dremel tool and filled in the small aperture, which was below the notch, with some J-B Weld. Now I have a true handgun rear-notch sight for this AR pistol, which is far more useful when firing one handed. I also mounted the rear sight opposite of what MFT recommends, as this gave me almost two inches of extra sight radius, and this does not affect the use of the sights. Now it's shooting time!

I chose Armscor 62-grain 5.56 FMJ as my test ammo and loaded up a Mission First Tactical Extreme Duty 30-round magazine and gave it a run. Everything functioned flawlessly, but the feel of this AR pistol was quite different from the others I own and fired, and it had to do with the trigger and recoil. To get a better idea as to what was going on, I loaded up a Magpul 20-round magazine and decided to also give the pistol notch sight a test at about 25 yards on a full-size 18” x 32” silhouette steel target. Shooting one-handed, it was no problem keeping the rounds on steel at this distance. I also noticed that the KynSHOT hydraulic buffer was reducing felt recoil, and I felt what was more of a smooth pushing feeling against my palm. I think I can even credit the buffer with the decrease in muzzle flip as well, since I only have a standard A2 birdcage flash hider screwed on. The trigger? I want one of these on all of my AR-15s (well, maybe not the retro ones). The very short trigger travel and reset with a crisp break at about three and a half pounds is a dream to press. I then turned and took the gun out to 50 yards on a smaller 12” x 20” steel silhouette. Using a traditional handgun two-hand hold with my left hand wrapped around my shooting hand, I took about 12 shots, and to my surprise, I think I only missed once. That is not bad for holding an AR pistol with arms extended and for a first attempt. If it hadn’t been for the handgun rear notch sight and the Midwest Industries trigger, I wouldn’t have been nearly as successful. Now for some bench shooting.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
DeNiro’s initial test of the handgun rear-notch sight was conducted on a full-size silhouette at 25 yards.
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Using a traditional handgun two-hand hold, DeNiro engaged a 12” x 20” steel silhouette target at 50 yards. The rear notch sight and Midwest Industries 3.5-pound trigger helped him maximize his shooting ability.

For my accuracy testing, I chose three loads: Winchester’s USA Ready 62-grain Open Tip (OP) .223 Patriot Defense 55-grain FMJ 5.56, and Barnaul 55-grain Boat Tail FMJ. Since this is a test of Aero Precision’s barrel and upper and not about my shooting abilities with 53-year-old eyes, I mounted a 14-power Bushnell Fullfield 30 scope. Now, Firearms News is not recommending that anyone mounts an optic like this on an AR-15 pistol, especially one with a 7.5-inch barrel, it was done solely for accuracy-testing purposes. My eyes aren’t what they used to be, so the extra magnification helps a lot with any accuracy test.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Test Ammo: Winchester’s USA Ready 62-grain Open Tip (OP) .223 (, Patriot Defense 55-grain FMJ 5.56 (, and Barnaul 55-grain Boat Tail (BT) FMJ ( The 14-power Bushnell Fullfield 30 scope is not practical (nor recommended) for this firearm and was used for accuracy-testing purposes only.

Getting into position with the sandbags was a bit of a chore especially since this AR pistol just has a buffer tube and a short barrel. Once I found the best position, I loaded up with five rounds of Winchester’s USA Ready 62-grain open-tipped ammunition ( I like the USA Ready line as the price is good and the ammo is a very good target load. My first group turned out to be the best of the day shooting a 1.06-inch group, and just under an inch without the flyer. The Midwest Industries trigger was a big help. My other group was at a little under two inches and the last one hit the1.06-inch mark again. Next up was Barnaul’s 55-grain boat-tail FMJ. The best out of the three five-shot groups measured in at two inches, which is great for an economy load. The other groups were at 3 ¼ and 3 3/4 inches. The best group for Barnaul without the flyer was 1 ¾ inches – pretty good! The last ammo to test is a new brand called Patriot Defense (, and I have the 55-grain FMJ. After the first shot I said: “Wow, this stuff is hot!” It was and is. The big red ball I saw through the optic was also impressive. I have not fired ammo this hot through an AR-15-type firearm since the early 1980s when my buddy (and first employer in the gun industry) Ken Foltz, of Ken’s Custom Cartridges, loaded some hot .223 for my AR-15. Anyway, my best group was 2 ¾ inches, without the flyer the best group was 2 7/16 inches. If you like your 5.56 hot, call Patriot Defense.


The short 7.5-inch barrel with 1 in 7-inch twist rate would probably be more favorable to a bit heavier load than 55 grain but all of the ammunition performed well – and no jams! I then removed the test scope and replaced it with the Aimpoint, took the Aero out to 75 yards, and fired at my 12”x20” metal target ( from a standing position. No problem hitting the steel. I then walked back to the 100-yard mark and used a tree to steady the Aero. No problem hitting the same steel target over and over – this can go in the bug-out bag!

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Winchester had the best five-shot group of that day at 50 yards with their USA Ready 62-grain open-tipped ammunition – 1.06 inches and only .94 of an inch without the flyer!

Certainly, the muzzle blast is an issue with this short of a barrel, and if my SHTF ammo was from Patriot Defense I would certainly have to address this issue. Firing any 5.56 ammunition from inside of a room or vehicle, without hearing protection, could send your brain into a dizziness that would rival getting a good right hook from a boxer. This is also the case with 10.5-inch barrels, and to mitigate against a really bad shooting experience, I have used Midwest Industries’ Blast Can, which directs muzzle blast forward and reduces the sound impact to your ears and head. Does it work? Yes! But, it does add more than a couple of inches to the overall length. Of course, you should always shoot with hearing protection on/in if able, or with a sound suppressor.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Midwest Industries’ Blast Can which directs muzzle blast forward and reduces the impact to your ears and head ($29.95, available at DeNiro has had one for years and recommends them for AR pistols.
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Aero SUV – A short AR pistol is really appreciated when you are driving and need the power of a 5.56. A small AR-15 pistol is less likely to get hung up on the steering wheel, dashboard, or windshield when firing from one open window to the next, or when exiting the vehicle.

For many survival situations, this 7.5-inch Aero Precision AR pistol would really be an upgrade to your everyday carry items. Is it a replacement for a full-size bug-out rifle if you live in the treeless plain states? No. But, within the cities of those plain states, it would have a great advantage over any traditional carry pistol, and in many states, it can be carried on your person, loaded and ready to go. You can’t travel with a rifle all the time, but with an AR-15 pistol, more avenues are open.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
The Aero Precision AR pistol ready to place into a survival kit…
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
…can be deployable in seconds.

If your state issues a concealed “weapons” permit, then most likely this would be the broadest definition of what you can carry concealed and may encompass almost any type of firearm. Other states use the federal definition of a handgun, so the overall length limit would be set at under 26 inches, which this configuration tested would fit just fine. [NOTE: Always measure your AR pistol with the muzzle attachment removed.] At least one state has a weight limit in its definition of a handgun (this Aero AR pistol build weighed in at 5 ½ pounds with an empty magazine), so most AR pistols would not qualify for CCW however, there are lightweight AR pistols that would be well under the weight limit if you live in, or plan to travel to/through, that state. South Carolina has a length limit of 12 inches for handgun CCW regulations, so the only way to get an AR pistol under or at that length would be to build a buffer tube-less AR pistol with a short bolt and a very short barrel. Then there are the “states behind enemy lines” whereby these firearms are unconstitutionally deemed as illegal. Be sure to research where you are travelling to ensure that an AR pistol can go with you inside of your bug-out bag.

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
If you ever have to abandon your vehicle and trek through the woods, an Aero Precision AR pistol will set your nerves more at ease in this or any survival situation. Also, be sure to have a water filter, fire source, compact food source, extra clothing like thermal underwear, a reliable handgun like this 9mm S&W M&P 2.0 with extra mags, first aid kit, as well as communications gear such as a MURS “walkie talkie”, VHF/UHF HAM radio, and a good AM/FM/Shortwave world band receiver. (Don’t depend on your smart phone!)
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
With both receiver assemblies separated, the Aero Precision AR pistol is even more compact for travel by air or car. Adding a .22 LR semi-auto conversion kit is also a great idea.

If you are looking for an AR pistol to add to your prepper arsenal, be sure to check out Aero Precision for high-quality options available not only in 7.5-inch barrel lengths but also in 8-, 10-, 10.5-, 11.5-, 12.5-, 14.5-, and 14.7-inch barrel lengths. The Aero Precision M4E1 Atlas S-One 7.5-inch barrel upper assembly, as tested, is priced between $404.99 - $429.99, depending on options. Aero Precision can be contacted at (253) 272-8188 or found on the web at

Kinetic Energy Tools Shell Deflector

Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
This photo, taken from video, shows the movement of the KET shell deflector and ejected case. If you reload your brass, or trade it in for more ammo, get one of these.
Aero Precision's M4E1 7.5-Inch Atlas S-One Pistol Upper
Top view of the KET brass deflector.

Kinetic Energy Tools’ Shell Deflector is a really nice brass deflector for those of us who either reload or save brass to trade in for new ammo. It comes with three different attachment parts which allow you to clip it onto scopes or a P-rail. The only issue I found is that you need to adjust it so that the brass doesn’t end up getting deflected on to your shooting hand, that can burn a bit or smack a knuckle. Once you have it set (Velcro allows for a wide range of adjustments), you are good to go. For more information go to:

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