Complete your AR build or refresh a worn lower with a dependable, all-in-one receiver extension solution: the ATI Outdoors Buffer Tube Kit (Mil-Spec). Designed to deliver the core components needed for a proper carbine-style recoil system, this kit includes a Mil-Spec buffer tube (receiver extension) along with the spring, buffer, locking ring, and nut, all finished in a clean black colorway to match most modern builds. Whether you’re assembling a new rifle, replacing mismatched parts, or restoring reliable function to a hard-used platform, the ATI Outdoors A.5.10.2240 / A5102240 (UPC 758152900470) provides a streamlined way to get your stock system and recoil assembly squared away with compatible Mil-Spec sizing.
If you’re searching for an ATI mil-spec buffer tube kit, a receiver extension kit with spring and buffer, or A5102240 758152900470, this is the exact product designed to match those keywords and deliver a builder-friendly package.
All-in-One Buffer Tube Kit: Everything You Need in One Package
Sourcing recoil system parts one-by-one can be annoying—and it’s easy to end up with mismatched specs. The ATI Outdoors Buffer Tube Kit simplifies the process by bundling the essential components you need for a standard carbine-style setup.
Included components (as listed):
This is ideal for builders who want a complete kit to finish a lower or replace components without piecing together multiple orders.
Mil-Spec Receiver Extension: Broad Compatibility for Stocks and Builds
A Mil-Spec buffer tube is one of the most common standards in AR builds. Choosing Mil-Spec sizing matters because it affects stock fit and overall compatibility.
Benefits of a Mil-Spec buffer tube:
Compatible with a wide range of Mil-Spec adjustable stocks
Standardized dimensions for easier parts matching
Great for new builds, rebuilds, and replacements
Helps avoid wobble or poor fit caused by mismatched tube/stock specs
If you’re building with common aftermarket stocks or want maximum compatibility, Mil-Spec is typically the right choice.
Reliable Function Starts with the Recoil System
The buffer, spring, and receiver extension work together to manage cycling, recoil impulse, and reliability. Replacing worn or unknown parts can improve consistency—especially for rifles that have seen a lot of use or builds assembled from mixed components.
This kit is a smart move when:
Your rifle has inconsistent cycling and you want a fresh baseline (after proper diagnosis)
You’re building a new lower and want matching components
Your buffer tube is damaged, out-of-spec, or heavily worn
You’re upgrading from an incomplete or mismatched setup
A solid recoil system foundation supports smoother operation and more predictable performance.
Black Finish: Clean Look That Matches Nearly Any AR Setup
Finished in black, this kit blends seamlessly with most receivers, stocks, and accessories. Black is the standard for a reason:
Matches the majority of AR furniture and receivers
Keeps a uniform look across your build
Hides normal wear and handling marks well
Looks right on both tactical and traditional builds
Whether you’re building a range rifle or a practical use carbine, black keeps your setup cohesive.
Ideal for New Builds, Replacement Projects, and Spare Parts Kits
The ATI Outdoors Buffer Tube Kit is a great fit for:
First-time builders who want a simple parts solution
Experienced builders assembling lowers in volume
Replacing unknown or worn recoil system parts
Completing a stripped lower receiver project
Keeping a ready-to-go kit in the toolbox for future builds
If you like having dependable parts on hand, this kit is an excellent bench staple.
Product Details for Search and Verification
Brand: ATI Outdoors
Product: Buffer Tube Kit (Receiver Extension Kit)
Spec: Mil-Spec
Includes: Spring, Buffer, Locking Ring & Nut
Color: Black
Part Number: A.5.10.2240 / A5102240
UPC: 758152900470
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…this is the exact product designed to match those searches.
For AR builders who want a convenient, compatibility-focused recoil system solution, the ATI Outdoors Buffer Tube Kit (Mil-Spec) delivers a complete package—including buffer tube, spring, buffer, locking ring, and nut—in a clean black finish, making it a smart choice for new builds, replacements, and dependable parts setups.
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