Premium A5 Buffer System Kit | Kratos, VLTOR, Sprinco, FCD

MSRP: $218.87
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This kit gives you everything you need for a complete A5 buffer system.

  • Kratos 8-position receiver extension
  • VLTOR A5H2 Buffer
  • Sprinco Green Spring
  • FCD CN5F Castle Nut
  • FCD ESF-H End Plate

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

  • Kratos 8-position receiver extension
  • VLTOR A5H2 Buffer
  • Sprinco Green Spring
  • FCD CN5F Castle Nut
  • FCD ESF-H End Plate



Kratos Buffer Tube

The Kratos Design Group A5 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


VLTOR Buffer:

Specifically developed on the request of the United States Marine Corps, the VLTOR A5 Buffer System is considered to be one the most beneficial upgrades to the AR platform in the last increasing the reliability, accuracy, and performance of AR pattern weapons.

NOTE: A5 buffers are only compatible with other VLTOR A5 buffer system components. The buffers themselves are longer than traditional carbine buffers, and they cannot be used in standard carbine receiver extensions.

  • A5H2: 5.33oz

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: 

CN5F (Castle Nut, A5, Forward Controls) is an extended version of CNF we’ve been making since 2018.  CN5F is designed specifically for the superb Vltor A5 system, CN5F is 0.1″ longer, and is as long as we can make a castle nut while ensuring backward compatibility, and the stock’s ability to fully collapse on Vltor’s RE-A5 and our RE5F.  Note: not all stocks will fully collapse on A5 compatible REs.   For more information on the differences between RE-A5, RE5F and RE10/A5SR, please follow this link:
CN5F aims to cover as much of the threaded area of a receiver extension (RE) as possible.  It could be made longer, but it will run into backward compatibility issues with some REs’ timing when installing the castle nut and end plate on the RE.  CN5F is made specifically for the Vltor A5 system, and it will allow even the longest carbine stocks to fully collapse on RE-A5 and our RE5F.  While CN5F will also work on standard TDP spec length RE, the additional length of the castle nut will prevent the carbine stock to fully collapse.

Other than its length, CN5F shares common features with its smaller brother, CNF.

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.CN5F (Castle Nut, Forward Controls) is based on the TDP spec castle nut, with couple of changes:

1. 0.1″ longer.
2. 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.
3. 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.
4. 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.


FCD ESF-H End Plate

ESF (End plate, Sling Adapter, Forward Controls Design) is a drop in end plate replacement for the AR platform (both 223 and 308 spec).  Featuring three quick detach sling swivel sockets (two side, and one rear facing), when used in conjunction with a castle nut, ESF will allow retractable carbine stocks to fully collapse.  SOPMOD and B5 Systems Bravo stocks will fully collapse with a rear facing QD swivel installed, other carbine stocks must be closed on the #2 position on the RE (#1 position being fully closed) if a rear facing QD swivel is present.
ESF is available in 7075 aluminum, anodized ESF-L (0.39oz), and 4140 steel, DLC coated ESF-H (1.10oz) versions.  Both ESF versions have rotation limited side facing sockets.  The rear facing socket has no limiters, as the receiver extension effectively limits the swivel’s rotation.  From late 2018, non-rotation limited side QD socket option has been deleted, all ESF-L and ESF-H have rotation limited side facing QD sockets)
We hesitate to call the 4140 ESF-H the “heavy duty” version, as it implies the 7075 ESF-L is a “light duty”, which it most assuredly isn’t.  Nothing about ESF-L’s 7075 construction makes it a light duty, it does make it lighter in weight.  H simply means Heavy, L means light.
4140 DLC coated ESF-H is no light weight at 1.1oz, almost 3 times as heavy as the 7075 ESF-L.  Our design philosophy focuses on utility, simplicity, and durability.  4140 ESF-H is heavy, because it is practically bomb proof, and will outlast the 7075 aluminum receivers.  Our concern with weight is only limited to keeping our designs as close to TDP weight as possible.  There isn’t a TDP equivalent for the ESF, and the 4140 ESF-H’s weight is centered on the AR, it will not cause the weapon to be front or rear heavy, thus we deem its heft to be acceptable, given its immense strength.
As is our practice, ESF’s shape is dictated by its functions.  In order to accommodate the rear facing socket, and fill one of the design requirements that ESF must be able to use stakable castle nuts and allow the carbine stock to fully collapse, ESF has a slight increase in width on the sides, and small openings on the top of the sockets housing.  These design cues do not affect ESF’s structural integrity, and mostly go unnoticed by users, they merely reflect a paradox, that it can be quite complicated to create a simplified design.  A seemingly simple product can often be more than meets the eye.
Aesthetics were never a part of the stated objectives for ESF.  Nonetheless, ESF, like similar products before it, effectively lengthens the carbine receiver’s rear and gives it a silhouette reminiscent of the classic AR10/SR25.  We’ve long considered the AR carbine’s rear seems to be abruptly terminated, which leaves a gap between the end plate and the carbine’s retractable stock.  ESF fills the void and, the classic AR15/M16 lines flow far better with it.  Even though we take a dim view of fashion firearms and components, we can still appreciate aesthetics, especially if they stem from the design’s functions ?



Additional information

Weight 6 oz
Dimensions 3 × 3 × 1 in

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