B5 Systems Sierra K Receiver Extension Kit SRK-1660 7075 Aluminum 5-Position Black
by B5 Systems
User Ratings
No ratings yet
Be the first to review this product
The B5 Systems Sierra K Receiver Extension Kit is the proprietary mounting system designed for the Sierra K Buttstock. Built from mil-spec materials and finishes, this reduced-length kit is engineered for compact builds while maintaining durability and reliable function. It includes a 5-position receiver extension made from 7075 aluminum, along with the key buffer system and mounting components needed for installation. Proudly made in the USA.
Product Highlights
- Proprietary Sierra K mounting solution featuring a reduced-length, mil-spec diameter receiver extension
- 7075 aluminum, 5-position receiver extension for strength and adjustable fit
- Includes short heavy buffer (3.5 oz) and extra power spring for dependable cycling
- Comes complete with castle nut and quick-disconnect (QD) end plate for secure mounting and sling compatibility
- Mil-spec materials and finishes; Made in the USA
Specifications
- Manufacturer:
- B5 Systems
- Category:
- buffer-tube
- Platforms:
- AR-15
- Weight:
- 3.5 oz
- UPC:
- 8227695067258
- MPN:
- SRK-1660
- Required Component:
- Yes
Parts Cabinet
Track parts you own or plan to buy.
Where to Buy
Have one to sell?
Sponsored
MantisX
The smart way to train your AR build
Built your rifle — now train it. BlackBeardX installs in minutes and turns your AR into a full dry fire system with smart feedback on every pull.
Shop BlackBeardXPrice History
Current
$128.25
Lowest
$102.60
Highest
$128.25
Price Alert
Sign in to save a target price and receive an email when this component drops.
Sign In to Set AlertWhat's Included in this Bundle
Similar Products

Aero Precision APRH101227C Enhanced Carbine Buffer Tube AR-15 AR-10
Aero Precision
$39.04

A5 Style AR15 Buffer Tube, 9-Position
Unknown
$39.95

Bravo Company 6-Position Receiver Extension, Black
Bravo Company Manufacturing (BCM)
$38.99

Aero Carbine Buffer Tube
Aero Precision
$39.99

Kratos Designs Group A5 Length Receiver Extension - Black Anodized
Kratos Design Group
$49.95

AR-15 Premium Buffer Tubes Mil-Spec
Geissele Automatics
$60.99

Geissele Automatics Geissele Premium MIL-SPEC AR-15 M4 DDC Buffer Tube 08-162S
Geissele Automatics
$61.99

PSA AR15 Premium MilSpec Diameter Buffer Tube
Palmetto State Armory
$16.99
Builds Using This Part
No builds yet — be the first to use this part.
Related Guides
Guide
AR-15 Armorer's Toolkit: What You Actually Need
A no-filler breakdown of the specific tools required for AR-15 armorer work, from trigger and grip swaps to barrel installation and headspace verification. What each tool does and why it matters.
7 min read
Guide
AR-15 Components: A Complete Reference Guide
A comprehensive overview of every major component in an AR-15 build—including what's inside bolt carrier groups and parts kits—organized by assembly for new builders.
12 min read
Guide
AR-15 Home Gunsmithing: What You Can Do Yourself
A practical breakdown of AR-15 maintenance and assembly tasks that are reasonable to tackle at home, what tools each requires, and where a licensed gunsmith belongs in the picture.
6 min read