In an AR-15 rifle, the buffer spring is the return or recoil spring that encircles the buffer and is housed in the buffer tube or receiver extension. In a self-loading firearm, the bolt or bolt carrier group’s return spring is compressed on its rearward stroke. Once fully compressed, the spring expands, driving the bolt group forward, which completes the operation cycle — feeding and chambering a fresh cartridge and closing/locking the breech.
Best .300 Blackout Buffer Springs
1. Aero Precision AR15 Carbine Recoil Buffer Spring
A manufacturer of parts for the aerospace and firearms industries, Aero Precision understands machining and engineering. Committed to exacting tolerances and quality control, Aero Precision produces high-quality AR-15-pattern rifles and spare parts at an affordable price.
If you’re building an AR-15-pattern carbine in .300 Blackout for the first time, choosing the correct buffer spring for your particular setup can be a daunting task because there are so many options, and the prices can vary, so start with the basics.
No buffer is included with this model, and if you’re looking for a spring that minimizes oscillation or noise, this isn’t it. This is strictly a no-frills, inexpensive compression spring manufactured to military specifications and designed to fit into a carbine-length receiver extension.
Regardless of whether you’re a beginner or experienced, the Aero Precision Carbine Recoil Buffer Spring is the default option. This is what you start with when you’re assembling a mil-spec weapon system.
2. JP Enterprises Tuned and Polished Buffer Spring
JP Enterprises, an industry leader in building competition rifles, also manufactures the parts and assemblies that make them work so well. The Tuned and Polished Buffer Spring represents an upgrade relative to the mil-spec product offered by Aero Precision, and this is reflected in the price.
The spring features a polished surface and consistent outside diameter to ensure it cycles smoothly and quietly inside the receiver extension. Centerless ground, JP Enterprises advertises this spring as improving the recoil impulse, resulting in faster sight recovery between shots and more reliable operation.
This is the buffer spring you buy when you only need the spring, but the mil-spec offering doesn’t provide you with the peace of mind you desire.
3. Nemo Arms 300BLK Custom Carbine Buffer Spring
This carbine-length buffer spring is designed specifically for the .300 Blackout cartridge by NEMO (New Evolution Military Ordnance) Arms. Manufacturing AR-10/15-pattern firearms in various calibers and configurations from .300 Blackout to .300 Winchester Magnum, NEMO’s product lineup shows the firm’s desire to push the envelope.
NEMO engineers the Custom Carbine Buffer Spring to accommodate .300 Blackout carbines and pistols that are undergassed. Undergassing refers to insufficient gas pressure delivered to the reciprocating action parts. This may be because of the size of the gas port, its distance from the chamber, the bolt carrier group’s weight, the type of ammunition used — especially low-pressure subsonic loads — or other factors.
NEMO’s buffer spring is designed for carbine-length barrels and gas systems, and because of its reduced stiffness, it can accommodate the lower pressures generated by subsonic loads. It is made from stainless steel, so the spring benefits from increased corrosion resistance and strength relative to uncoated spring steel.
If you’re assembling a .300 Blackout carbine for use with a sound suppressor, this spring allows you to cycle subsonic loads, keeping your weapon as silent as possible.
4. Geissele AR-15 Super 42 Buffer Spring/Buffer Combo
Geissele Automatics is a manufacturer of premier AR-15-pattern rifles and trigger mechanisms founded in 2004. Since 2005, Geissele has been supplying match-grade trigger assemblies to U.S. special operations forces. This commitment to quality extends to other firearms parts.
Designated the Super 42, the braided-wire spring design is inspired by the system used on the WWII-era German MG 42 machine gun. The braided design incorporates 3 separate wire strands and allows the spring to dampen the harmonics and absorb energy more efficiently because each strand can flex independently of the whole. Geissele has combined the braided buffer spring with an H1 buffer.
The Super 42 produces approximately 15% greater force on the return stroke than mil-spec buffer springs, so the company doesn’t recommend using low-pressure .300 Blackout subsonic loads. If you’re primarily interested in firing supersonic .300 Blackout ammunition, this shouldn’t be an issue.
Geissele designed the Super 42 Buffer Spring/Buffer Combo to be used in a carbine-length receiver extension (i.e., buffer tube), so it’s not compatible with a rifle-length extension.
5. JP Enterprises Gen 2 Silent Captured Buffer Spring System
A common complaint among those who shoot AR-15-pattern weapons is that the buffer spring’s reciprocation causes excessive noise. This is due, in part, to the oscillation of the spring as it compresses and expands. Another cause is the buffer spring rubbing against the inside of the receiver extension.
For years, JP Enterprises has been perfecting its rifle cycle, ensuring a glass-like action that defines smoothness. One of the motives behind this has been to reduce the sound of what president John Paul describes as a wood rasp.
Using a captured return spring, the system is inserted into the receiver extension as a single unit. The buffer spring coils never contact the inside of the extension, so one source of noise is eliminated.
Another advantage of using a captured spring is that there’s no way the spring can fly out of the buffer tube during disassembly.
If you notice a rattling sound, that’s from the weights inside the buffer. JP Enterprises has left some free movement to maximize the so-called dead blow or anti-bounce effect. To reduce the noise, JP can provide you with an additional O-ring. The free movement can be reduced but should still decrease the bouncing effect enough for most weapons systems.
While designed for a carbine-length receiver extension, JP includes a spacer for rifle-length systems.
6. Strike Industries AR Carbine Flat Wire Spring
Another option for increasing the buffer spring’s service life while simultaneously reducing the distracting twang is the Strike Industries Flat Wire Spring. Strike Industries has developed a reputation for designing innovative parts and accessories for rifles and handguns.
This buffer spring uses a flat wire rather than the traditional single-strand round or the braided type. Strike manufactures the flat-wire spring from 17-7 PH steel and cryogenically stress relieves the material to maximize the spring’s longevity and reliability.
The flat-wire spring lessens the oscillation associated with the traditional buffer spring and cuts down on the vibration of the reciprocating action parts, which allows for a smoother operating cycle.
A flat-wire spring has a shorter solid height than a round-wire spring of equivalent coils when fully compressed. That means that a flat-wire spring can generate a comparable amount of force in a smaller amount of space. Another advantage of the Strike Industries buffer spring is that it requires less force to compress but generates more bolt load, ensuring positive feeding, chambering, and locking every time.
What Does a Buffer Do?
The buffer is a metal sleeve containing a series of weights, usually made of steel and tungsten, which control the bolt carrier group’s rearward acceleration by adding mass.
When firing, the powder gases expand the cartridge case in the chamber, sealing the breech. Ideally, the bolt will not unlock and attempt to extract the spent cartridge until the chamber’s pressure has fallen and the case has time to contract. Depending on the gas system and other factors, such as the ammunition and the bolt carrier group’s weight, you may require a heavier or lighter buffer.
If the buffer is too heavy, the action may short cycle, failing to extract or eject the spent cartridge or not clearing the magazine long enough to allow the feeding spring to raise the successive cartridge into alignment with the chamber. A too light buffer may open the action too early, causing inconsistent ejection or damaging the extractor groove.
Why the Buffer Spring is Important
In a handheld firearm, the recoil spring is necessary to facilitate self-loading operation, and there is a limited amount of space to fit compression springs. As a result, the design and choice of material that comprise the recoil spring are essential to ensure reliable functioning. The demands placed on the buffer spring depend on several factors, the same as the buffer. These include:
- Length of gas system: The gas port placement relative to the chamber, described as rifle, carbine, or pistol length. The closer the gas port is to the chamber, the higher the gas pressure. When using subsonic loads, placing the gas port closer to the chamber compensates for the comparatively lower pressure. The barrel length also affects the dwell time of the gas in the bore.
- Gas port size: The gas port’s distance from the chamber and diameter also play a role in the cycle. The gas port size directly affects the pressure and volume of the gas fed into the action.
- Type of ammunition: The cartridge’s operating pressure and the specific load you’re using affect the weapon’s cycle.
- The bolt carrier group’s weight: Mil-spec or skeletonized ultra-light competition, the static inertia of the reciprocating action parts work in tandem with the ammo and the buffer system.
- Muzzle device: A sound suppressor that uses a series of baffles to capture the burning propellant’s expanding gases maintains pressure in the bore for longer. This can cause the weapon to cycle more violently and may necessitate using a heavier buffer or buffer spring.
Don’t underestimate the importance of the buffer spring to the reliable operation of an AR-15-pattern rifle, carbine, or pistol. A return spring is essential to the functioning of a self-loading firearm, and this is no different. Many types of buffer springs suit different calibers, barrel lengths, gas systems, and other factors.
Buffers also need careful attention because they’re designed to control the bolt carrier group’s acceleration when the weapon is fired. Some actions need a light buffer to cycle reliably. Others need a heavy buffer to ensure that the breech doesn’t open too quickly. These systems work together, and you need to find a combination that produces a harmonious result in your particular configuration.