B5 Srk-1660 Srk Extention Kit Blk
$128.25
$135.00
(You save
$6.75
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The B5 Systems SRK Extension Kit is the complete receiver extension system designed specifically for the SRK (Sierra K) buttstock platform. If you're building or upgrading an AR with a quality stock that actually feels right in your hands, you'll need this kit—it's the foundation that makes the whole setup work. B5 built this as a proprietary mounting system, which means the parts are engineered to work together as a unit, not thrown together from generic AR parts.
Everything here is mil-spec materials and finishes, and B5 makes them in the USA. The extension itself is a 5-position design in 7075 aluminum, giving you length-of-pull adjustability to dial in your fit whether you're wearing body armor, a heavy coat, or just a t-shirt. What sets this kit apart is that B5 includes the right buffer for their system: a short heavy buffer (3.5 oz) that's matched to work with the included extra power spring. Both are in the box. You also get the castle nut and quick-detach end plate, so assembly is straightforward if you know your way around an upper and lower.
This is the gear you grab when you want a stock setup that works instead of one that fights you. The SRK buttstock itself has earned a real reputation for ergonomics and durability, and this extension kit is built to the same standard. Whether you're running a precision rifle, a duty gun, or a do-it-all carbine, having the right receiver extension matters more than most shooters realize—it affects how the whole rifle balances and cycles.
Key Features
- 5-position adjustable length for customized fit across different body armor and clothing
- 7075 aluminum construction for durability and weight management
- Mil-spec materials and finishes throughout
- Short heavy buffer (3.5 oz) tuned for SRK system performance
- Extra power spring included for proper cycling
- Castle nut and QD end plate for quick-detach capability
- Made in the USA
Specifications
| Brand | B5 Systems |
| Model | SRK-1660 |
| Color | Black |
| Material | 7075 Aluminum |
| Positions | 5 |
| Buffer Weight | 3.5 oz (short heavy) |
| Included Components | Receiver extension, short heavy buffer, extra power spring, castle nut, QD end plate |
| Finish | Mil-spec |
| Country of Origin | USA |
Frequently Asked Questions
Is this kit compatible with standard AR-15 uppers and lowers?
The SRK Extension Kit is a proprietary mounting system designed for the B5 Systems SRK buttstock platform. Verify compatibility with your specific stock and upper/lower combination before purchase.
What's included in this kit?
You get the 5-position receiver extension, a short heavy buffer (3.5 oz), an extra power spring, a castle nut, and a quick-detach end plate. Everything needed for assembly is in the box.
What does the 3.5 oz buffer do?
The short heavy buffer is part of the SRK system's tuning and affects how the rifle cycles and feels during recoil. It's matched to work with the included extra power spring for proper function.
Can I adjust the length of pull?
Yes. The extension offers 5 positions for adjustable length of pull, letting you customize fit for different loads, body armor, or clothing.
