UTG Pro AR-15 Ops Ready S4 Mil-Spec Stock Kit – Buffer Assembly Included

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Compact AR-15 Stock Kit for CQB and PDWs

The two-piece S4 stock comes with a complete set of all the parts you’ll need for finishing off your AR-15’s recoil system.  This kit includes the buffer tube, carbine buffer weight, buffer spring, castle nut, and endplate, ready to install on your lower of choice.  The S4 stock slides in with four-position adjustment with its unique, ultralight design, which is great for short AR builds where staying compact is key.

Four position adjustment with extreme low profile.

The detachable cheek piece enhances cheek weld, with a 2.23″ forward offset to aid in comfort and consistency. Simply adjust the cheek piece to where it’s the most comfortable by sliding it into the channel in the main portion of the stock.  The stock also features a reversible QD sling cup in the rear, as well as a loop for traditional mounting.

If you’re interested in the stock by itself, check out the S4 stock in Black or Flat Dark Earth.


  • Stock Material: Polymer
  • Buffer Weight: Carbine (3.0 oz)
  • Diameter: Mil-spec
  • Stock Height: 4.75″
  • Stock Length: 4.28″
  • Weight of complete kit: 17.1 oz

Have Questions About this Product?

The AT3 Tactical store has a 90 day no-hassle return policy for products in good condition. You can view the full details of our return policy here.

If you encounter an issue or defect with a product after 90 days of your purchase, you can refer to the manufacturer for a warranty claim. Their policies are below.

UTG Lifetime Warranty

Leapers, Inc. warrants that all UTG & UTG PRO products conform to published specifications and are free from defects in material and workmanship. We will repair or replace defective products for the duration of the product’s life span. Our dedicated in-house customer service professionals will provide the best-in-class UTG experience.

Please note that this warranty does not extend to products disassembled, damaged from misuse, accidental impact, negligence, natural disasters/accidents, or unauthorized repair or alteration.

Warranty Instructions

  • Go to Warranty Request under Customer Service on our website.
  • Fill out the necessary contact and product information to the best of your knowledge.
  • A purchase receipt is required for all warranty cases and needs to be attached at the end of the form.
  • Finalize the case by submitting the information to us.
  • You will hear from one of our customer service reps within 24-48 hours and we will provide you with additional information and instructions.
  • No return will be accepted without an RA#.
  • For any questions regarding the process, please feel free to call at (734)542-1500.

Disclaimer: Manufacturer’s warranty is subject to change without prior notice.

Customer Reviews

Based on 11 reviews
Honzik Frystacky
UTG Pro AR-15 S4 mil-Spec stock

Great stock, easy to put on. Great price. Matches my lower and upper parts perfectly and looks great. Super comfortable.

Giovanni Orta
S4 Mil Spec Buffer kit

In love with it. Fits perfectly and looks great!

Thank you for your kind words! We're glad you're happy with your purchase.

Zackery Martinez

It works like it should. I have noticed with some carving handles they come in contact with the charging handle.

Roberto Martez
OG rob

Very happy nice nice looks good on my 300 blackout

Thanks for sharing your feedback! We're glad you're satisfied with your purchase.

Tony moss
Ok - probably best for a side charger

Standard charging handle hits the cheek riser. Purchased for an AR build. Will end up on one of my side Charging AR9 or 223.