A5 Buffer System Kit | Kratos, Sprinco, FCD, SOLGW, BCM

MSRP: $165.95
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This kit gives you everything you need for a complete A5 buffer system.

  • Kratos 8-position receiver extension
  • SOLGW T2 Buffer
  • Sprinco Green Spring
  • FCD CNF Castle Nut
  • BCM QD End Plate
(4 customer reviews)

This kit gives you everything you need for a complete A5 buffer system.

  • Kratos 8-position receiver extension
  • SOLGW T2 Buffer
  • Sprinco Green Spring
  • FCD CNF Castle Nut
  • BCM QD End Plate



Kratos Buffer Tube

The Kratos Design Group 8-position Receiver Extension is fully compatible with VLTOR’s patented A5 system. This receiver extension is slightly longer than the traditional M4 receiver extension to utilize rifle length springs and A5 buffers and is designed to work with Mil-Spec dimensioned M4/AR-15 type collapsible stocks.  For AR15/M16 applications, it must use Vltor A5 or A5 compatible buffers & rifle length recoil springs We reccomend the Sprinco Green Spring for most applications.

This receiver extension tube can also can be utilized as a replacement receiver extension for the AR-10 rifle.

Dialing in the perfect length of pull is easy with eight adjustable stock positions.

The Kratos Design Group buffer tube is made of impact-extruded 7075 Aluminum and is made to withstand rigorous use. The finish is a Type III Class 2 hardcoat anodize. 

Weight: 4.3oz
Material: Impact-Extruded 7075 aluminum
Finish: Type III, Class 2 hardcoat Anodize
Made in USA


Sons of Liberty Gun Works Buffer T2:

For years we have been well known for our bundled “A5KIT’s” offered – allowing users to purchase one kit to install an A5 (intermediate) length receiver extension on the lower receiver. We have introduced the SOLGW T2 Buffer.

The SOLGW T2 buffer (5.6oz) is offered as a stand alone option to tune AR pattern rifles that are already equipped with the A5 receiver extension/ recoil system. This allows fine tuning for optimal reliability and ejection pattern on rifles that are over gassed whether suppressed or unsuppressed.

To meet our current demand schedules for these kits, as well as the rifles built using them, we have partnered with BCM to offer our own version of their MK2 Recoil Management System. This 5.6oz (T2) buffer is a drop-in replacement for the A5H2 weight the majority of our rifles have been shipping with for almost 10 years now.

  • Lessens felt recoil, without compromising reliability
  • Provides a more consistent carrier velocity, which can aid in accuracy, reliability over conventional carbine buffer system
  • Increased internal counterweight travel reduces bolt bounce
  • Uses a M16A4 rifle spring with more spring coils than M4 carbine, increases consistency and widens operating envelope
  • Internal spring to reduce noise of counter weight shifting and ensure more consistent weight placement

Sprinco Green Spring:

Sprinco AR-15 rifle buffer springs are made from high quality Chrome Silicon wire stock. Sprinco heat treats, shot peens, and treats each spring with a proprietary formula that retains spring efficiency for as long as you have your rifle. The Sprinco Green rifle buffer spring is a great option to improve the long-term reliability of your AR-15.


  • For rifle length buffer tubes
  • Color-coded green
  • Standard power
  • Made from chrome silicon wire stock
  • Heat treated and shot-peened

Sprinco has extensively tested this setup and have concluded that it works great with the VLTOR A5 stock setup. It also helps you to easily identify which power spring you have in your AR-15 if you have a habit of changing your setup constantly.


Forward Controls CNF: 

Call us old fashioned, we like our castle nut staked to prevent it from rotating loose on the receiver extension and causing malfunctions. Army manual calls for the castle nut to be staked in two places. While we’re not in the “more is better, bigger is better” camp, there are times less isn’t more.

The TDP spec castle nut is a simple and robust fastener that is almost perfect for the job it’s tasked to perform. Over the years, we’ve consistently come up with two minor gripes, first is its staking notches seem rather shallow and short, second is we don’t enjoy using the castle nut’s wrench notches as serrations (our fingers invariably find their way to these sharp cutouts) to rotate it towards to the end plate while installing it.

CNF (Castle Nut, Forward Controls) is based on the TDP spec castle nut, with couple of changes:

1. Staking notches angle changed from 45 to 30 degrees, this results in longer (25% longer than TDP spec) and deeper notches than found on TDP castle nuts.
2. Number of staking notches increased from 3 to 4, spaced equally on the CNF. The castle nut is to be staked in two places, we’re not advocating staking in more than two places, CNF’s 4 staking notches mean that, at all times, 3 will be visible and available for staking, it simply gives the user more staking location options.
3. Coarse serrations on the wrench side of the nut, a single use feature to make it easier while rotating the CNF towards the end plate.

It is our opinion that a castle nut should be staked per TM, CNF’s longer and deeper notch reinforces the belief, that once installed and staked, it will not loosen without the user’s deliberate action. We love the idea of quick detach, but some things on an AR are meant to stay put, and considerable effort was made to ensure that by the original designers. CNF is a continuation and evolution in that direction.

CNF is billet machined in 4140 PH steel, and black nitrided. As with everything Forward Controls Design produces, it is proudly made in the USA.

We’d like to thank Ash Hess for letting us use parts of the Army/Air Force / Navy TM for CNF’s installation instructions, on the back of the card.


BCM QD End Plate

BCM® Receiver End Plate with socket for Quick Disconnect (QD) swivel.

Machined from steel, and easily accommodates staking.

Like all BCM products, Made with pride in the U.S.A.



Additional information

Weight 6 oz
Dimensions 3 × 3 × 1 in
Receiver Extension Color

Black Anodized, OD Green Anodized, FDE (Type 1) Anodized, FDE (Type 2) Anodized

4 reviews for A5 Buffer System Kit | Kratos, Sprinco, FCD, SOLGW, BCM

  1. Sergie Bodunov (verified owner)

    Great kit. One stop shop for all your quality components for a A5 system

  2. Frank Kaczmarczyk (verified owner)

    Everything works so well together! Another fine Big Tex kit!

  3. kcf197 (verified owner)

    Best value and high-quality kit to get into the A5 system.

  4. zuke0099 (verified owner)

    Solid kit if you’re looking to swap to an A5 system. My only nitpicks would be that 1. The FCD castle but included is not the A5 length version (still works though) and 2. I prefer the Geissele braided rifle spring for it’s lack of sound, but the sprinco is still a great spring. I love the Kratos tube, it fits a B5 SOPMOD stock more snugly than I’ve ever seen, made me fall in love with the stock all over again. This was definitely easier than piecing it all together on your own.

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