AIM7 AR-15/M16 Buffer Tube Kit with Flat springs, 3 hole buffer, IronKeep Castle nut

Categories: , , , , SKU: A2188-2689-2739-2740-1



Combo Includes:


  • Spring. Aim7 Flat Spring
  • 3 oz buffer, black
  • Castle nut (IronKeep)
  • Standard end plate

Since the introduction of the AR-15 in the 1950s, round wire springs have served as the standard. However, our Enhanced Flat Wire Spring surpasses traditional options like music wire, stainless steel, and chrome silicon in several aspects. Unlike round wire springs, our Flat Wire Spring applies greater pressure on the bolt when in battery, slightly increasing bolt lock time and subsequently lowering chamber pressures prior to extraction. Moreover, it aids in smoothly returning the bolt to the battery under adverse conditions and fouling, facilitates the extraction of stubborn rounds from magazines, and may even contribute to reducing the bolt.

The benefits of a flat buffer spring are numerous. Firstly, its design allows for more consistent and even pressure distribution compared to traditional round buffer springs. This can result in smoother cycling of the firearm, reducing felt recoil and muzzle rise. Additionally, flat buffer springs tend to be more durable and resistant to deformation over time, ensuring reliable performance even after prolonged use. Furthermore, their construction often allows for easier installation and maintenance. Overall, the flat buffer spring offers enhanced reliability, durability, and shooting comfort compared to its round counterparts.


  •  AR-15/M6 Enhanced Flat Wire Buffer Spring
  • Optimized for Carbine Length Buffer Tubes
  • SU304 Stainless Steel Construction
  • Improved Spring Load Characteristics
  • Reduces Bolt Bounce
  • Reduces Spring Rattle
  • Lifetime Warranty
  • Weighs 2 oz

Bolt Forward in Battery:

Mil-Spec     ~ 10 – 10.34lbs F1=46.17+-7.32N

Bolt Locked to Rear:

Mil-Spec     ~ 14 lbs -F2=63.76 -+7.77N


Recommended Uses:

Use our AR-15 Enhanced Flat Wire Buffer Spring on any gas-operated small frame AR calibers such as:

  • .223 Rem/5.56 NATO
  • 6mm ARC
  • 22 Nosler
  • .224 Valkyrie
  • Supersonic 300 Blackout
  • 6.5 Grendel
  • 6.8 SPC
  • 7.62×39
  • 9mm PCC straight blowbacks
  • etc.

DO NOT use the following:

  • Receiver Extensions Shorter than Carbine Length
  • Subsonic 300 Blackout
  • AR-10/SR25 or any Large-frame AR’s
  • .308 Win/7.62×51 NATO
  • 6.5 Creedmoor
  • .260 Remington
  • .243 Winchester
  • etc.

AR15/.223 6 PT Mil-Spec Fluted Buffer Tube

Designed from the ground up to be feature-packed, our 6 Position Mil-Spec Anti-Friction Fluted Buffer Tube is a must-have for any hardcore AR enthusiast. Machined with ten recessed channels that provide both weight and friction reduction, this buffer tube will allow even the tightest Mil-Spec stocks to slide with ease.

  • Recessed pockets for weight reduction
  • 3 drain holes for marine environments
  • Type III hard-coat anodized 6061-T6 aluminum
  • 6 position Mil-Spec diameter buffer tube
  • Accepts all Mil-Spec stocks
  • AR-15 & AR-10 compatible
  • Weight: 3.2 oz

HK 416, MR556 A5 Style Extended Length Castle Nut for mil-spec tube only.

(will not fit Pistol buffer tubes)

Our HK A5 extended buffer tube castle nut will fit both mil-spec. This is the best option for those doing a 416A5 build so it can be a correct build. All Steel 17-4 manufacture. Each castle nut is made to the same specs and materials as the HK 416A5—a rare offering in the USA.

Made from ordnance 17-4 grade steel.

Compatible with:

  • AR15/AR308/AR10/AR9 ETC.
  • HK MR556, CR556
  • HK 416
  • HK M27
  • HK 416-A5
  • Other AR, M4 & other M16 projects
  1. Securing the Receiver Extension: The castle nut is used to secure the receiver extension (buffer tube) to the receiver of the rifle. It is threaded onto the end of the buffer tube and tightened against the receiver to ensure a secure connection.
  2. Preventing Rotation: Once properly tightened, the castle nut prevents the receiver extension from rotating or coming loose during the firing or handling of the rifle. This is crucial for maintaining the alignment of the buffer tube and the stock, ensuring proper function and stability.
  3. Retention of Other Components: In some designs, the castle nut may also serve to retain other components of the buffer tube assembly, such as the end plate or receiver end plate sling adapter.
  4. Compatibility: The castle nut is designed to work specifically with the receiver extension and other components of the rifle’s buffer tube assembly. It is manufactured to precise specifications to ensure proper fit and function.
  5. Durability: Like other components of the rifle, the castle nut is made from durable steel, ensuring strength and reliability under the stresses of firing and regular use.


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