CMMG AR-15 Mil-Spec Carbine Buffer Spring 55CA9A2

Overview of the CMMG Carbine Buffer Spring | 55CA9A2

The CMMG AR-15 Carbine Buffer Spring is one of those components you only think about when it starts to fail. Part number 55CA9A2 from CMMG is a precision-wound stainless steel replacement spring built to meet or exceed mil-spec performance standards for the AR-15 platform.

Seated inside any standard carbine buffer tube, this spring works with your buffer to manage bolt carrier group travel, absorb recoil, and return the BCG to battery after every shot. When a worn or out-of-spec spring is in the mix, you notice it fast: short-stroking, inconsistent ejection, and failures to feed.

Trusted by:

• Law enforcement officers building or maintaining AR-15 duty carbines
• Military veterans and active-duty personnel running the AR-15 platform
• Armorers, competitive shooters, and gun enthusiasts doing builds or routine replacements

Made in the USA by CMMG, a trusted name in AR-15 manufacturing, the 55CA9A2 is a straightforward, no-modification drop-in for any AR-15 equipped with a carbine-length receiver extension.

Key Features

• Material: Stainless steel construction resists corrosion and maintains spring tension through extended use
• Performance Standard: Meets or exceeds mil-spec requirements for AR-15 carbine buffer springs, ensuring compatibility and reliability on duty-grade and service-grade carbines
• Compatibility: Fits any AR-15 equipped with a standard carbine-length (collapsible stock) buffer tube, both mil-spec and commercial-spec diameter tubes
• Function: Controls BCG travel during the firing cycle, absorbs recoil energy, and provides consistent return force to push the bolt back into battery
• Drop-In Installation: No modifications required; installs in minutes with basic field tools
• Country of Origin: Made in the USA by CMMG (Fayette, Missouri)
• Replacement Interval: Inspect every few thousand rounds; proactive replacement is recommended for duty, defensive, or high-round-count competition rifles

Specifications

Compatibility

The CMMG 55CA9A2 is designed to fit any AR-15 platform equipped with a carbine-length receiver extension (the style used with adjustable/collapsible stocks). It is compatible with both mil-spec and commercial-spec carbine buffer tube diameters.

This spring is not compatible with:

• Rifle-length buffer tubes (those require a longer rifle-length buffer spring, approximately 12.75 in.)
• AR-10/LR-308 platforms (which use a different spring specification)
• PDW-specific or ultra-compact receiver extensions that require manufacturer-specific springs

If your AR-15 uses a collapsible stock on a standard 6-position carbine receiver extension, the CMMG 55CA9A2 is the correct spring format for your setup. Pair it with a carbine-length buffer assembly for best results.

Intended Users

The CMMG AR-15 Carbine Buffer Spring 55CA9A2 is built for anyone who demands reliability from their AR-15 platform.

Law enforcement officers who carry or qualify with an AR-15 patrol carbine rely on every component performing correctly under stress. Replacing a worn buffer spring is a routine but critical part of keeping a duty rifle in top condition.

Military veterans and active-duty service members familiar with the AR-15/M4 platform understand the importance of mil-spec components. The CMMG 55CA9A2 meets that standard and installs with the same ease as any mil-spec replacement part.

Competitive shooters and high-volume range shooters put their carbines through round counts that wear out springs faster than casual use. A fresh CMMG spring maintains consistent cycling and helps eliminate the spring noise (known as twang) that develops in older, fatigued springs.

Home builders and armorers completing or repairing an AR-15 lower need a reliable buffer spring from a manufacturer known for quality. The CMMG 55CA9A2 is a trusted component in both new builds and maintenance kits.

What's Included

• 1x CMMG AR-15 Carbine Buffer Spring (MPN 55CA9A2)

Not included: buffer assembly, carbine buffer tube/receiver extension, end plate, castle nut, or stock. These components are sold separately. If you are doing a full buffer system build, pair this spring with a compatible CMMG carbine buffer assembly and carbine receiver extension.

Available at WCUniforms

WCUniforms is a veteran and law enforcement-owned specialty retailer serving first responders, military professionals, and working civilians across the United States with uniforms, tactical gear, and public safety equipment. The CMMG AR-15 Carbine Buffer Spring 55CA9A2 ships from our Michigan location, and we stock it as part of our ongoing selection of trusted AR-15 components for professionals who depend on reliable gear. Unlike generic replacement springs of unknown origin, the CMMG 55CA9A2 comes from a U.S. manufacturer with a documented track record in the AR-15 space. Shop with confidence at wcuniforms.com.