Selecting an AR Buffer Spring
Short Story: Buffer springs are an important component in the AR. Spring selection can be used to fine tune the operation, but must be approached carefully and with consideration to the rest of the system.
Buffer springs are part of the operating system of an AR.
This article is an extension of our discussion on reciprocating mass (bolt carrier group and buffer) and the gas system. It is helpful to understand how the gas system and reciprocating mass work in concert before continuing on to the buffer spring, so please review our Mass and Gas article.
As the reciprocating mass moves rearward under the force delivered by the gas system, the buffer spring compresses. As the buffer spring compresses, it absorbs and stores the kinetic energy of the reciprocating mass. As the reciprocating mass slows to a stop, the loaded spring releases the stored kinetic energy back into the reciprocating mass, driving it forward again. It is this release of energy that drives the reciprocating mass forward, strips the next round from the magazine, and puts the bolt back into battery.
Spring weight can have significant impact on performance and perceived recoil.
Before we proceed, a note about terminology: when we say “bolt lock time”, we are referring to the time during which the bolt is locked after the cartridge is fired (i.e. the time from the moment the firing pin strikes the primer to the time that the bolt disengages the locking lugs of the barrel extension). We do not mean “lock time” as in the time from pulling the trigger to the moment the firing pin strikes the primer; this is important, for sure, but is not what we are talking about.
A lighter spring will:
- Decrease bolt lock time. This will begin the cycling of the reciprocating mass sooner. Be aware that too short a bolt lock time may result in popped primers and a shorter bolt life, due to the higher chamber pressure when the bolt begins to move out of battery.
- Cause the reciprocating mass to begin moving rearward sooner, accelerate faster, and reach the rearmost position sooner. As such, the rearward recoil impulse will happen earlier.
- Absorb a higher proportion of the kinetic energy toward the end of the compression cycle, resulting in a higher perceived rearward recoil impulse.
- Cause the reciprocating mass to accelerate slower from the rearmost position, travel forward at a slower rate of speed, and take more time to complete the forward stroke. As such, the forward recoil impulse will will be delayed relative to the start of the forward stroke.
A heavier spring will do just the opposite:
- Increase bolt lock time. The reciprocating mass will remain in battery longer, which will allow the chamber pressure to dissipate before the extraction begins.
- Reciprocating mass will begin moving rearward later, accelerate slower, and reach the rearmost position later. As such, the rearward impulse will be delayed.
- The spring will absorb the kinetic energy more evenly throughout the compression cycle, resulting in a distributed and lower perceived rearward recoil impulse.
- Reciprocating mass will accelerate faster from the rearmost position, travel forward at a faster rate of speed, and take less time to complete the forward stroke. As such, the forward recoil impulse will occur in earlier relative to the start of the forward stroke.
In most situations, our advice regarding spring weight is consistent with our advice for the entire operating system: use the heaviest combination that allows your gun to cycle reliably. This will generally result in a better shooting experience, better accuracy, and greater reliability.
But, be careful not to go too heavy. Too heavy a spring for a particular load will cause issues, because the gas pressure will not be able to drive the reciprocating mass hard enough to compress the spring fully. This can lead to failure to extract, failure to feed, and failure to lock back after firing the last round from a magazine. It is important to understand that every cartridge/load and setup will have different needs; what works with standard 5.56 NATO round will not necessarily work with .300 Blackout subsonic round; what works in an unsuppressed gun will not necessarily be ideal for a suppressed gun.
Beyond the power of a spring, the design and quality of the spring can have significant impact on the consistency and reliability of the operation. A quality spring will move easily within the receiver extension and will load and unload kinetic energy consistently. Consistent management of kinetic energy means smoother recoil and more reliable forward force to put the gun back into battery.
Buffer Springs generally come in 4 varieties: round wire, twisted wire, flat wire, and captured.
Round Wire
Your standard AR buffer spring is a round wire spring. There is absolutely nothing wrong with round wire buffer springs. They do the job, and do it well.
You can certainly upgrade your Mil-Spec round wire spring with a better round wire spring. Sprinco manufacturers an awesome line of AR buffer springs in varying weights. Their line of springs come in 6 weights for the carbine AR, allowing even better fine tuning of recoil and cycling performance. The springs are color coded for easy identification (in and out of the factory), and come in the following options:
- Yellow: 20% lighter than standard (White).
- White: Standard equivalent to a Mil-Spec M4 carbine spring.
- Hot White: Intermediate spring weight between White and Blue.
- Blue: 15% heavier than standard (White).
- Red: 25% heavier than standard (White). Great for 9mm, 6.8 SPC, 6.5 Grendel, .450 Bushmaster, .458 SOCOM, .50 Beowulf.
- Orange: Standard for DPMS LR-308 pattern AR-10 and for over-gassed AR-15 setups.
- Green: Standard for AR-15 caliber rifles.
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Twisted/Braided Wire
The Geissele Super 42 is the standard when it comes to braided springs (though competitors like Armaspec$ are entering this market). It boasts a 3-wire twisted spring (designed after the springs used in the German MG42 machine gun) that is 15% more powerful than a standard round wire spring. The 3-wire design reduces the spring “twang” heard/felt with a standard spring and the extra power of the spring more effectively absorbs the recoil and delivers a more forceful forward impulse to put the gun back into battery.
Geissele offers the rifle spring alone and the carbine spring paired with a Geissele buffer. They offer the carbine spring paired with H1, H2, and H3 buffers.
Given the characteristics of this spring (higher spring power), selection of buffer weight deviates a bit from the standard spring weight. To address this, Geissele has provided guidance on the appropriate buffer weight for use with the Super 42 spring in various setups.
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Flat Wire
Flat wire springs address some issues presented by round wire springs. Specifically, the stability (think of a stack of donuts vs. dinner plates) and stress placed on the spring during compression. In addition, the characteristics of a flat spring can improve the overall performance of the system.
As a flat wire spring compresses, it buckles (lateral displacement) a lot less than a round wire equivalent. This lateral stability equates to a more consistent and quieter operating AR.
The compressed (solid) length of a flat wire spring is significantly less than that of a standard round wire spring (see image below).
There is less internal material stress in the rearmost position, which increases the longevity of the spring (David Tubb claims that his springs are rated 500,000 cycles; this is a bold claim, but we have no reason to doubt it and no intention of testing it).
The free length of flat wire springs is typically significantly longer than that of a standard round wire spring. This results in more applied pressure to the bolt when the bolt is in the forwardmost position, and this tension resists the bolt moving out of battery, which increases bolt lock time for a given gas pressure. This increased bolt lock time contributes to better accuracy (delayed movement of the reciprocating mass = better internal ballistics).
Because the free length of flat wire springs is longer, the bolt tension is greater, and the compression of the spring occurs more gradually, a flat wire spring can better distribute the recoil impulse throughout the range of compression, which can reduce perceived recoil.
There are two manufacturers of flat wire springs that we can recommend.
- David Tubb: David Tubb makes the best flat wire springs out there; these are the gold standard in flat wire springs. They are offered in both AR-15 and AR-10. Note that for each AR class, the spring fits both carbine and rifle receiver extensions.
- Strike Industries: SI has produced a solid option in the realm of flat wire springs. SI offers these springs in both AR-15 and AR-10 versions. Note that the AR-10 spring fits both carbine and rifle receiver extensions, while the AR-15 Carbine spring is designed specifically for the carbine-length receiver extension. Some complain that these springs increase the buffer spring “twang”, while others experience just the opposite (we are in this latter group). These polar opposite experiences probably have more to do with the receiver extension than the spring itself, because the principle design of a flat wire spring should reduce the lateral displacement of the spring during compression, and it is this wobbly compression that causes the spring to rub on the receiver extension and make the metallic “twang”. Either way, the functional benefits of a flat wire spring are offered in this product.
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Captured
If you’ve heard of a captured buffer spring, you’ve probably heard of the JP Enterprises Silent Captured Spring.
The captured buffer spring is fundamentally different, when compared to every other option. As the name suggests, the spring is captive. Beyond the obvious, this is an entire buffer system. The spring and buffer weights ride over a central rod and are self-contained within the system. As the spring compresses, it is held in place, axially, by the central rod, which prevents it from rubbing on the side of the receiver extension. The overall result is an extremely consistent, tunable, and quiet (hence JP’s naming) buffer system.
As the bolt carrier advances into the receive extension, the central rod on the captured spring feed through the opening in the rear of the bolt carrier, while the buffer presses against the rear face of the bolt carrier. This is fundamentally different than the standard buffer/buffer spring setup. No benefit, but a consequence of the central rod and something to be aware of.
The only downside to a captured buffer spring is the cost. A standard Mil-Spec carbine buffer spring and buffer will run you about $15 combined. A JP SCS system will cost nearly 10 times that.
The two best options for captured buffer spring systems are:
- JP Enterprises: The Silent Captured Spring system is hands down top notch and has been around since 2012, so it has been running in ARs for a long time. You will pay a premium for this premium performing option, but if you are building a gun for performance, it can’t be beat. JP offers this system in both AR-15, AR-10, and AR-9 classes, in standard and H2 buffer weight equivalents, and with either one or multiple spring weights (AR-15: 5 springs; AR-10: 3 springs).
- Armaspec: The Stealth Recoil Spring (SRS) is Armaspec’s answer to JP Enterprise’s SCS system. It follows a similar design and is well-received in the market. It is also significantly less expensive than the JP system (retail $84.99 vs $139.95 for an analogous system), though still a bit more than $15. Armaspec offers this system in both AR-15, AR-10, and AR-9, and the AR-15 version is offered in standard, H1, H2, and H3 buffer weight equivalents, as well as a kit containing standard, H1, and H2 weights.
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* Requires an A2 spacer, sold separately HERE.