By Toby Melville
March 10, 2020
Last updated on 3/10/20.
The AR-15 is arguably one of the most prolific and modular rifles ever created. Not only has Eugene Stoner’s creation been in service for over 55 years, to date, the AR-15 sets the standard for accuracy, reliability, and modularity by which all modern rifles are measured. Due to the AR-15’s modular design, it’s allowed various manufacturers to develop an entire industry around the platform. The AR-15 is not only iconic, but also a customizable platform that can be tailored to any specific need of the user.
With so many choices available to the user, how does one choose what’s best suited to their individual needs? The answer to this question can be researched through numerous experts and peers, but, in the end, it’s the end user that will have to decide what works best for them. This article isn’t meant to discuss in detail the rabbit hole of ballistics or the endless accessories that are available for the AR platform. The intent is to provide end users with a clearer picture of possibilities of the platform in a specific realm. I’m going to box in the conversation by focusing on a growing market of popularity: the pistol and short-barreled rifle.
It’s easy to see why so many are interested in the short-barreled AR. It’s a modern departure from the 1980s battle rifles seen throughout the world. We can call this an evolution of both the platform and the ammunition used today. The short-barreled AR offers light weight, ease of use, and improved maneuverability. The short-barreled AR also adds a look that is so often seen in television, cinema, and video games. Whether one is building a short-barreled rifle or pistol, there are some important facts one should consider before your next build or purchase. Other than wanting an AR that looks the part, it’s important to start with a need or intent.
The AR design was built around specific requirements. The AR had to be lightweight, accurate, easy to use, allow for more ammunition to be carried, and cause serious injury more than lethality. The AR was designed around a 55gr (grain) 5.56mm NATO (5.56x45mm NATO) cartridge and a barrel length of 20 inches. The 5.56mm cartridge showed its best performance with a 20-inch barrel. The combination of velocity and barrel length allowed this lightweight cartridge to optimize its performance, especially since the 55gr round was inherently unstable.
Editor’s Note: It should also be noted that the original AR-15/M16 was designed to fire 5.56mm ammo using clean and fast-burning stick powder, and not ball powder. The U.S. Army’s decision to use ball powder is what caused most if not all the AR-15/M16’s initial combat reliability issues, and necessitated chrome-lining the chamber and barrel.
When the barrel is shortened the performance is degraded. This is where the search engine on your computer can help minimize the legwork. When looking up terminal velocity for the 5.56mm round, we can see that 2,500 fps is the threshold below which the bullet’s terminal ballistics start to quickly decline.
That said, it’s important to weigh out the pros and cons of owning a weapon with a shorter barrel than it was intended to have. To start with, the AR platform with a short barrel will offer better performance with a rifle cartridge than it will with a pistol cartridge. Comparing a longer barrel in a pistol cartridge to a shorter barrel in a rifle cartridge you will find that the rifle cartridge still creates more velocity. This means that you can still have improved performance out of a shorter barrel, and take advantage of all the benefits of a shorter, lighter weapon. For example, a 9mm cartridge with a 16 inch barrel will still not meet the same velocity or penetration as a 5.56mm cartridge with a 7.5 inch barrel.
While the 5.56mm cartridge fired out of a 7.5-inch barrel can only reach approximately 2000 fps, it still offers improved performance compared to a 9mm cartridge. The reason the 5.56mm cartridge looses so much velocity is the lack of time the bullet spends in the barrel. The time spent in the barrel is referred to as dwell time. Dwell time can be broken down into two areas. The first is when the cartridge is fired and the bullet is being pushed down the barrel up to the gas block. This is where the expanding gas is partially redirected back into the weapon in order to make it cycle, so it can load another cartridge.
The second part is post gas block; this is the remaining barrel that is left for the bullet to travel down and leave the barrel. This section is important because it’s where the last part of stability and velocity come from. With a 20 inch barreled AR, more powder is burned, and the additional barrel length gives the bullet plenty of stability before some of the gas is redirected back into the weapon. The distances of the barrel and gas block are specific, and based on the cartridge fired. The 5.56mm cartridge is optimized in this configuration, and provides its best performance.
Now that we’ve looked at how the barrel affects the performance it’s time to examine three very popular barrel lengths for the AR chambered in 5.56mm. The barrel lengths we will examine are 7.5 inches, 10.5 inches, and 12.5 inches. The 12.5-inch barrel is not as common, but is growing in popularity for many reasons. By looking at the pros and cons of each length, you’ll be able to make a more accurate decision as to which barrel length will meet your needs. The 7.5 and 10.5-inch barrel lengths are both now common, but the 10.5, and even the 10.3-inch barrel, can be argued to have the greatest popularity due to their common use, seen with both the military and law enforcement. The biggest advantage of the 10.5 and 10.3 is that they combine a lighter weight with improved handling and maneuverability. The 5.56mm bullet does lose a lot of velocity, but it’s still able to reach 2,400 feet per second (fps), giving this bullet plenty of stopping power, if not optimal power.
This is where the 12.5-inch barrel offers some advantages over the other platforms as an improved all-around barrel length. On average, the 12.5-inch barrel allows for an average of 2,500 fps with a variety of bullet weights. And, with its shorter barrel, weight is reduced and handling is improved over longer barrel lengths. Since the 5.56mm bullet is reaching that magic velocity of 2,500 fps the bullet has a specific feature it was designed for. At the point of 2,500 fps the bullet is designed to tumble when it strikes its target. This is referred to a yaw. Yaw is the destabilizing of the bullet in its target causing increased damage by shredding its way through the target, and easily changing direction if it hits anything hard, like bone. This increases both lethality and injury to the target.
Now, we see how there is a trade off between the barrel length and the necessary velocity for the weapon’s intended use. The 7.5-inch barrel offers incredible maneuverability with light weight. However, its engagement distance is limited due to massive velocity loss. The 10.5 offers good maneuverability and improved velocity, but still lacks the ability to offer the true performance of the 5.56mm cartridge. The 12.5-inch barrel on the AR offers excellent velocity at short and even longer ranges, delivering terminal velocity that both of the other barrel lengths are not able to reach, and still offers improved handling and reduced weight over the standard military length of 14.5 inches, and the standard civilian 16-inch required by law.
The 12.5 therefore gives the shooter the best of both worlds. You get reduced weight, improved handling and terminal velocity, all rolled into one package. This is where the user has to choose between increased size and weight with a loss of power, improved power with good size and weight reduction, or having optimal power with good maneuverability and weight reduction. Each of these has excellent applications, and I own all three for specific reasons.
The 7.5-inch AR is optimized for confined spaces and home defense in urban and suburban areas. When working in vehicles where the occupants sit inside the vehicle, the 7.5 offers excellent maneuverability, and reduces the chance of becoming hung up on objects like a steering wheel, seats, or center console. The 7.5-inch does however have its drawbacks, with limited effective range and penetration, due to its decreased velocity.
The 10.5-inch AR shares improved maneuverability in confined spaces, but is not as easy to wield as the 7.5. However, it allows for increased lethality at distance, as well as full use of most 5.56 suppressors (silencers/sound suppressors), given the increased dwell time. Most 5.56mm suppressors are not rated for 7.5-inch barrel lengths, due to the lack of dwell time and and the fact that they can become seriously damaged. Both of these barrel lengths offer excellent handling with decent velocity, and offer superior ballistics when compared to pistol caliber offerings.
The 12.5-inch AR is more of a multipurpose platform. It will give its user terminal velocity, ensuring maximum damage on target. And, if configured correctly, it’s still easy to wield in tight spaces or confined environments. While its reduced weight lessens fatigue over prolonged use, it’s extra barrel length ensures it can still have intended affects on target, even at distances out several hundred meters away. This barrel length is also compatible with the use of suppressors, and will better conceal muzzle flash with a wider variety of muzzle breaks and flash hiders. One thing that has not yet been discussed with all three of these barrel lengths is choosing a muzzle break or compensator. Really, for the sake of argument, there is no real difference between the two, it’s two different names for the same affect.
If you intend to use your short-barreled rifle or pistol in confined spaces, like home defense or in or around a vehicle, the use of an inline compensator may be your best choice. These are designed to push all of the flash forward and away from the shooter, directly to the front. This is advantageous when shooting next to people, in tight spaces, or from inside a vehicle. The chance of blowing glass into you, unnecessarily damaging your vehicle, or burning or disrupting adjacent shooters will greatly enhance your capability, but will increase felt recoil. On the other hand the 12.5 is 5 inches longer than the 7.5, and is still 2 inches longer than the 10.5. Depending on the compensator used, this can be enough to make a difference when working around vehicles, in tight spaces, and still offering a larger choice of effective compensators.
Another factor is rail space. Rail space is the total Picatinny (MIL-STD-1913) rail length offered on both the upper receiver and the handguard. Longer barrels will obviously offer the option for longer handguards. With all shorter-length rails, the stacking, or as I refer to it as a “ladder” effect, is the front-to-back stacking of accessories needed for different uses. If someone is just an occasional shooter, having just an optic or even iron sights will be fine, even with something as short as a 7-inch handguard, but this space is at a premium if more is needed by the user. The 10.5 with a 10-inch handguard is still pressed for space if the user is a professional or has the same needs. The application of back up iron sights (BUIS), an optic, light, and day/night laser quickly makes the user have to carefully plan which brands and types of products one may be able to employ, based on his/her needs.
The use of a 12-inch handguard on the 12.5 AR is a little more forgiving, thanks to its additional 2-plus inches. Again, the user will need to consider what’s actually needed versus what’s applicable. For a functional all-around short-barreled AR-15 SBR (Short Barreled Rifle) platform, the 12.5-inch barrel provides a 4-inch reduction from the military M4/M4A1 Carbine or AR-15 equivalent using the standard 14.5 inch barrel. This length provides great velocity, and makes the weapon lighter and handier than the 20-inch M16-styled platform as well.
I’ve taken the liberty of providing you the reader with three examples. All three ARs are built around the now extinct Legion Arms billet lowers left over from a previous purchase with Midwest Industries (MI) complete upper receivers. Midwest Industries provides quality and precision with a price point that’s extremely competitive. MI also offers a massive selection of accessories and rifles, and I commonly use their weapons and own several in 5.56 and .308 Win./7.62mm NATO (7.62x51mm NATO). All three are using the MI suppressor-compatible hand guards with MI flip-up iron sights, which DefenseReview (DR) has covered in with great photos and video.
Bullet Proof Arms (BPA) in San Antonio, Texas painted all three weapons. BPA is a veteran-owned and operated establishment that has a solid reputation for quality and honesty with everything they sell. The 12.5-inch AR barrel is from Ballistic Advantage, and the compensator is a dual-port Sig Sauer muzzle brake. The lowers of the 7.5 and 10.5 have upgraded lower parts kits with the Maxim Defense Telescoping CQB SB Tactical braces, and the 12.5 is using Dead Foot Arms MCS with an SB Tactical SBA3 brace. The optic on the 7.5 is a Vortex Crossfire red dot, and the 10.5 and 12.5 utilize a 1x Cyclops from Primary Optics, and are coupled with their 3x Magnifier with Flip Mount. This allows for identifying targets at longer distances easier.
The pistol grip on the 12.5 is from Executive Ordnance, and all three platforms benefit from Railscales polymer handguard scales. Railscales has created many amazing products, and continues to offer top of the line products at very fair prices. The angled grip on the 12.5 is their Anchor, and has been paired with their Carve hand stop. This allows for exceptional hand placement and weapon control. The other angled grip is from Lage Manufacturing and is exceptional for multiple platforms. The final piece of equipment on the ARs would be Bad Company Tactical’s Rapid Retention System, or R2S. The new Gen-2 system allows for mounting multiple accessories in one spot to save space, and is customizable by the end user. The Dove Tail interacts with the Base Plate and allows for fast and extremely strong reliable retention to keep weapons or equipment retained, or out of the way until needed.
Author’s Note: The grid system used on the seats and the back of my body armor is from Grey Man Tactical. I’ll be doing an article on them soon, as well.
Company Contact Info:
Midwest Industries, Inc (MI)
W292S4498 Hillside Rd.
Waukesha, WI 53189
Email Contact Page: http://www.midwestindustriesinc.com/index.cfm?fuseaction=page.display&page_id=33
Grey Man Tactical
Email: [email protected]
PO Box 2845
Claremore, OK 74018
General Inquires / [email protected] / 918-973-2910
Product Development / [email protected] / 918-973-2911
OEM Vendors / [email protected] / 918-973-2912
Dealer/LE/Gov Sales / [email protected] / 918-973-2910
Replacement Hardware / [email protected] / 918-973-2914
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