Upgrade your rifle with a complete, ready-to-install stock solution built for modern AR owners: the Leapers, Inc. UTG Model 4 Combat Ops S1 Stock Kit (RBUS1BM | UPC: 4717385550896). Designed as a 6-position Mil-Spec stock assembly, this kit provides the core components you need to outfit a compatible AR-style lower with a functional, adjustable stock system—ideal for new builds, replacement projects, or upgrading a basic setup. Finished in classic black, the UTG Combat Ops S1 kit delivers practical adjustability, a clean tactical look, and convenient “all-in-one” value.
If you’re searching for a UTG stock kit, a Mil-Spec 6-position stock assembly, or a complete AR buffer tube kit with stock, the RBUS1BM is a smart choice for builders who want the essentials bundled together.
Complete 6-Position Mil-Spec Stock Assembly Kit
One of the biggest advantages of this product is that it’s a stock kit, not just a stock body. That means it’s designed to deliver a more complete solution for AR builders and owners who want to install or replace a full rear stock system without piecing together individual parts.
This kit includes:
For many builds, these are the critical components that determine how the rifle fits the shooter, how it cycles, and how durable the rear assembly feels. Having them together in one kit helps reduce guesswork and simplifies planning.
6-Position Adjustability for Fit, Comfort, and Control
An adjustable stock is one of the most useful features on an AR-style rifle. The 6-position design lets you quickly change length of pull to suit:
Different shooter sizes
Body armor or heavy outerwear
Preferred shooting stance (upright, bladed, squared)
Confined spaces or transport needs
Whether you’re setting up a general-purpose carbine, a training rifle, or a home-defense-oriented build, the ability to adjust stock length improves comfort and helps create a more consistent cheek weld and shooting position.
Mil-Spec Fitment for Broad Compatibility
This kit is described as Mil-Spec, which is important because Mil-Spec receiver extensions (buffer tubes) are a common standard used across many AR parts and accessories. Choosing Mil-Spec fitment helps ensure compatibility with a wide range of Mil-Spec-pattern stocks and components, making it a solid foundation for future upgrades or changes.
Includes Extension Tube, Buffer, and Buffer Spring: Core Components for Function
The stock assembly isn’t just about comfort—it’s tied directly to the rifle’s cycling system. By including the extension tube, buffer, and buffer spring, this kit supports a complete functional rear-end setup for compatible AR platforms. That’s especially helpful if you’re:
Building a new lower from scratch
Replacing worn or mismatched components
Standardizing parts on a rifle with unknown history
Refreshing a budget build with a cohesive kit
Castle Nut and Tear-Drop Ring Included for Proper Assembly
Builders know the small parts matter. This kit includes the castle nut and tear-drop ring, both essential for correctly securing the receiver extension assembly. Having these included means fewer extra parts to source and a smoother build process—especially for first-time builders or anyone wanting a clean, complete installation path.
Black Finish: Clean, Tactical, and Easy to Match
The black finish gives this UTG stock kit a classic look that matches most AR receivers, handguards, and accessories. Black is the go-to choice for many builders because it’s:
Low-profile and professional
Easy to pair with nearly any rifle theme
Durable and practical for hard-use rifles
Whether your build is minimalist, duty-styled, or purely range-focused, the black Combat Ops S1 kit blends in cleanly.
Why Choose the UTG Model 4 Combat Ops S1 Stock Kit?
This kit is designed for shooters who want a practical stock solution that includes more than just the stock body. It’s a strong option for value-focused builds where you still want dependable parts and modern adjustability.
Ideal for:
AR builders who want a complete Mil-Spec stock kit
Replacing a worn buffer tube system and stock in one go
Setting up a training or general-purpose carbine
New AR owners who want adjustability and a straightforward install
Key reasons to choose it:
All-in-one kit reduces sourcing hassle
6-position adjustability improves fit and comfort
Mil-Spec spec helps with compatibility
Includes critical parts: tube, buffer, spring, castle nut, and ring
Product Details for Easy Identification and Reordering
Use the identifiers below to confirm you have the exact kit:
Brand: Leapers, Inc. / UTG
Model: Model 4 Combat Ops S1 Stock Kit
Type: 6-position Mil-Spec stock assembly kit
Finish/Color: Black
Includes: Extension tube, buffer, buffer spring, tear-drop ring, castle nut
Part Number: RBUS1BM
UPC: 4717385550896
These details help with accurate listing verification, inventory management, and reordering.
A Complete, Builder-Friendly AR Stock Kit with Mil-Spec Adjustability
The Leapers, Inc. UTG Model 4 Combat Ops S1 Stock Kit (RBUS1BM) is a practical, ready-to-install solution for AR owners who want a 6-position adjustable Mil-Spec stock assembly with the components that matter most included in the box. With its black finish, complete buffer tube system parts, and builder-friendly package, it’s an excellent choice for new builds, replacements, and upgrades where simplicity, compatibility, and value are top priorities.
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