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AR-15 A5 Type Buffer Systems - Development and Innovations

Updated: Mar 1, 2023

VLTOR Buffer System (Left) and Carbine Buffer System (Right).

carbine vs A5 buffer tube
Normal Carbine Buffer Tube (Left) is shorter than the A5 Buffer Tube (Right)

Decades of development and testing have driven the AR-15 platform to be a highly refined tool. As of late, few significant improvements have been made to the platform, forcing users and the industry to focus in on fine, technical details. This has resulted in products like the A5 type of enhanced buffer systems, from manufacturers like BCM and VLTOR. This enhanced buffer system allows for the mechanical system of the AR platform to be further optimized and refined in a meaningful way. Understanding how and why such an improvement can come about is key to the development of small arms, both presently and into the future.

Lead up to the invention of the A5 Buffer System

The A5 system is a direct result of the U.S. Marine Corps desire to blend the reliability and smoothness of the M16 rifle length buffer system, while providing the mission flexibility the shorter carbine length buffer tube system provided the M4 carbine. Taking a step back in time, seeing developments that were made in the early and mid 2000s, the Marine Corps was looking to upgrade their existing inventory of M16A4 rifles. The Marine Corps wanted to maintain 20” barrels in order to maximize ballistic performance of the 5.56x45mm cartridge. The U.S. Army had been upgrading, experimenting, and innovating on the M4 platform, the select fire carbine variant of the AR-15 family. The carbine, the accessories, and all the aftermarket support that grew up around the M4 showcased how modern small arms needed to have a more versatile and mission configurable layout.

The USMC also began to find the M16 rifle was not the best weapon to use in conjunction with body armor, especially as not all service members are the same shape or size. As armor adds height to a user's chest, the full-length stock made this configuration especially awkward for a small statured Marines. It could also cause problems for users when they were firing the weapon from unconventional or unbalanced positions, as is often found in the dynamic environments found in modern combat. Again, the USMC wanted to find solutions without compromising the reliability and durability of the M16A4, and the Marine Corps would put out an official request for information to find a viable solution. (It is important to note the USMC requests at this time also included other features and upgrades to the weapons; we are omitting them in this article to focus on the A5 concept and system.)

The VLTOR A5 Buffer System is Born

In 2009 VLTOR stepped up to the challenge presented by the request from the USMC and pioneered the A5 system; “The VLTOR A5 Buffer System is basically a proprietary buffer and receiver extension tube that are intermediate in length. The buffer and the tube are both 3/4 of an inch longer than a standard carbine buffer set up. The system also utilizes a rifle action spring instead of a carbine spring.

VLTOR found this configuration did not degrade reliability, while also giving the host M16 rifles the ability to accept an adjustable stock like the M4. VLTOR opted to call this new product and system the A5, as it was thought to be the natural progression for the M16 to go from the A4 nomenclature to the A5, once this product and others were adopted for the next evolution of the M16 platform.

The A5 Buffer Tube (aka the Receiver Extension)

FCD A5 Buffer Tube
Forward Control Designs A5 Buffer Tube, notice the wider castle nut which allows more thread engagement to the receiver.

The A5 system can be described as an intermediate buffer system, since it is longer than a carbine system, but shorter than the rifle system. The 8” buffer tube allows for Milspec pattern stocks to be used, allowing for the collapsed position to be shorter than any fixed stock variants, but also extend out past the length of pull of any rifle stocks. Many shooters know the shortest positions on a carbine length buffer system cannot be used comfortably to fire from, and therefore the A5 in its shortest configuration is about the same length as the shortest practical length of pull used by most shooters utilizing a carbine length buffer tube. The A5 buffer tube uses standard Milspec castle nuts and end plates, making it an easy upgrade to add to most AR-15 pattern weapons.

A5 Buffers

A5 and Carbine Buffers
A5 Buffer (Left) and Carbine Buffer (Right)

In order to maintain balance within the system, the buffer and spring also need to differ from standard configurations. The system does incorporate a rifle length recoil spring, but it uses a longer intermediate buffer. This buffer is longer than a carbine length buffer, but is far shorter than a rifle length buffer. The A5 buffer also incorporates 4 internal weights, instead of the 3 found in a carbine buffer. This allows for additional weight to be used, thus allowing for carrier speed to be more smoothly controlled in its rearward travel, while also assisting in loading and chambering of the next round. The A5 buffer can also incorporate heavier weights, with the spread being from 3.80 oz up to 6.83 oz (a standard carbine buffer is about 3.25 oz). This buffer and weight configuration also further enhances the dead-blow characteristics of the buffer, assisting in reliable chambering and lock-up of the bolt into battery.

A5 Springs

A5 and Carbine Buffer Springs
A5 Buffer Spring (Left) vs Carbine Buffer Spring (Right)

The rifle spring the A5 system uses also assists in the recoil and cycling process, which results in a smoother and softer recoil impulse; the increased length and coils allows for a more controlled and constant compression and rebound, even with the increased buffer weight. As a result, AR-15 pattern firearms equipped with an A5 system do not wear certain components as much as a traditional carbine length buffer system. It is also important to note the A5 system can be used on AR-15 pattern rifles which utilize traditional gas-impingement or gas-piston operated recoil systems, as the bolt travel and forces need to achieve this are not really changed by the way in which the gun is cycled.

A5 Stocks

VLTOR paired the A5 system with their Enhanced Modular Stock, or EMOD. The A5 EMOD has seven positions of adjustability. Fully extended, the length of pull (LOP) is 15.25”—longer than an A2 stock for those who need it. Moving into Position 5 (the receiver extension is marked with the number visible through a witness hole on the EMOD stock) yields about the same LOP of a standard A2 stock. Position 2 results in about the same length as an A1 fixed stock. All the way collapsed gives a LOP of 12.38” or about the same length as the third position out on a four-position M4 stock. The fully collapsed A5 stock setup takes the overall length of a rifle with a 20” barrel down to 37.25” or about 2.25” shorter than a fixed A2 stock rifle.

These stocks come in black, tan, or green, and interface the best on A5 length buffer tubes. They also feature a partially enhanced cheek piece and slightly longer toe, which double as waterproof battery storage compartments. The EMOD stock also incorporates a QD socket and molded loops to allow for a variety of ways to mount slings. The A5 system can also accept a variety of Milspec stocks, although some will collapse too far inward, which results in the longer buffer tube sticking out the back of the stock.

What about an M4 Lower on an M16 Upper?

Some readers and AR tinkerers may be wondering why the USMC, or any military force, would not just simply ditch fixed stocks and fit the rifles with carbine length buffer tubes, stocks, buffers, and springs? Simply put, putting a carbine length buffer system on a Milspec M16 rifle is not inherently reliable. Testing showed these hybrid configurations, effectively an M16 upper of an M4 lower, do not always work well together. This configuration was found to be very susceptible to bolt bounce, especially in full-auto use.

Bolt Bounce

Bolt bounce occurs when a firearm using an autoloading system does not have sufficient mass behind the bolt to reliably load and chamber subsequent rounds; the weapon is fired, the bolt unlocks and moves rearward, the spent casing is pulled from the chamber, ejected, and after full rearward travel occurs, the bolt and recoil system move forward, stripping the next round from the magazine. However, upon chambering the round the bolt moves slightly rearward, then back fully into battery. This phenomenon is easily recorded and documented using high speed videography, and many videos have been made on this subject. This issue results in hammer follow and the weapon will not fire reliably.

Timing Issues

Other problems with this proposed off the shelf configuration deal with timing within the system. The weights and lengths of travel can also result in highly erratic cyclic rates which not only increases the recoil impulse, but also makes the weapon wear out components faster. Inconsistent ejection patterns can also be a side effect of these issues, and once more will reduce the weapons reliability and performance. The lack of consistent and predictable timing to this configuration renders it virtually useless for military purposes, only being a viable setup for users who have the time and resources to tune each individual weapon.

Results of Military Trials and Testing

Getting back to the development saga, the next major set of information about the A5 system came out in 2013. Extensive testing proved the VLTOR A5 system could hold up to military standards. The data from these tests appears to still be controlled by the DOD, but it is widely known the A5 outperformed all other systems used during these small arms weapon trials, including more traditional rifle length systems; “There’s a ton of things that it does simultaneously, some more nuanced than others. But the synopsis is it regulates carrier velocity, changes felt recoil impulse, and most importantly, it opens up the entire operational envelope of the gun. It allows the gun to run properly under a much wider range of input and factors. This usually equates to more overall reliability which is a good thing.”

Ultimately, the Marine Corps would go on to not adopt the A5 system or any major upgrade packages for their M16A4 rifles, instead opting to procure brand new M4 pattern carbines for the force. The M16 was still retained, but is used in fewer and fewer roles by the USMC. Further military testing resulted in most forces utilizing an H2 carbine buffer to reduce recoil, improve feeding, and decrease the risk of bolt bounce. This was clearly not the optimal solution, but a much cheaper and cost-effective means to achieve somewhat similar results. Interestingly enough, the Canadian military was also experimenting with buffer system upgrades around this time, retrofitting some of their C7 rifles with shorter recoil systems, but coming to a similar conclusion and opting to gradually issue out only C8 carbines.

Commercial Acceptance

With the A5 concept not finding widespread military adoption, the concept and products were instead embraced by the firearms industry. VLTOR was the first company to really pioneer both the concept and to balance the recipe. The company now sells a variety of parts and pieces for the VLTOR A5 family. They sell full kits with stocks, as well as spring and buffer kits, and also just the A5 buffer tubes. VLTOR also makes an AR pistol buffer tube which omits any type of length of pull adjustment by utilizing a traditional round pistol buffer tube.

Buffer Springs made by Geissele, Sprinco and VLTOR
Geissele, Sprinco Green, and VLTOR Buffer Springs


The VLTOR A5 family of parts has also seen widespread use from custom/premium AR-15 manufacturers like Sons of Liberty Gun Works. Furthermore, VLTOR and other A5 parts are not terribly expensive; “It’s also worth noting the cost of the A5 components aren’t really much higher than carbine buffer components of comparable quality. If you price out a nice set of carbine buffer components from one of the big guys, full retail is around $80 for a carbine extension, carbine spring, and H2 buffer. Full retail on an A5 extension, A5 spring, and A5H2 buffer is right around $100. The return on that extra $20 investment is insane."

VLTOR Weapon Systems


Since there is nothing proprietary to the A5 concept, BCM is another company who has opted to support the A5 concept. BCM brands their system as the BCM MK2, with the whole kit being called the BCM MK2 Recoil Mitigation System. The specifications on this kit are similar, incorporating a longer buffer tube, longer buffer, and longer buffer spring, as compared to the carbine length recoil system. BCM also offers multiple recoil kits, as well as the buffers, buffer tubes, and recoil springs so users can tune their weapons. Just like with the VLTOR components, specific stocks and hardware can be interchangeable, allowing users to fully customize their setup. Magpul, Colt, LMT, as well as some other companies have also made components or kits over the years around the A5 concept.

Practical Applications

Radian A-DAC 15 Lower with VLTOR A5 System

The A5 concept and the host of parts around the system have allowed users of varying backgrounds to make the best use of the system. For many early users, the smooth reliable attributes of the A5 system enhanced the performance of both carbine and rifle setups, driving innovation and performance. Mid-length AR gas systems also began to become popular, and pairing this gas system with an A5 recoil system further optimized carbine setup.

The greatest catalyst as of late though has been the continued growth of shooting with suppressors/silencers. Just as the AR-15 and other weapons saw a renaissance in the mid to late 2000s, the utilization of NFA regulated products, mainly weapon silencers (and to a lesser extent SBRs, SBSs, AOWs, etc.) has caused the A5 system to become even more relevant over the past decade. Many silencers efficiently reduce muzzle rapport, but in doing so increase back pressure within the weapon system. This increase in gas and pressure can adversely affect the function of an AR-15 or any other autoloading firearm. The A5 concept has been proved to help mitigate this issue by allowing for the use of heavier springs, buffers, and a longer bolt-travel distance, all of which are inherent attributes of A5 specification components, to tame these additionally forces.

Final Considerations

The A5 buffer system, first pioneered by VLTOR for the United States Marine Corps, is considered by many to be one of the few significant upgrades to ever be introduced to the AR-15/M4/M16 family of firearms. The A5 system incorporates a longer buffer tube which can still accommodate the telescoping stock of the M4, while increasing the spring and buffer length to function almost as smoothly as the rifle recoil system found in the M16. This system was not formally adopted by the USMC, as they opted to order M4 carbines and then branch out into different weapons and concepts like the M27.

However, the criteria, engineering, and testing all ensured the A5 concept would find favor amongst other parties, chiefly the civilian market. The system would first find favor with users looking to optimize carbine setups, but would grow even more in popularity as silencers/suppressors gained widespread popularity. Ultimately, this concept and the components which create this mechanical system are an extremely well thought out and innovative solution to the perpetual problem of balancing the internal system of an automatic small arm.

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