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U.S. Arms M4 Builder Set


ATF regulated items have restrictions and requirements:

  • Your order will ship only to a Federal Firearms License holder.
  • We are not currently shipping to CA, CT, DC, HI, MD, MA, MN, NJ, NY, or VA.
  • Please be sure to contact your local FFL dealer prior to placing your order to ensure they are still accepting transfers. Some FFL dealers are not open due to Covid-19.
  • Customer must read, understand, and agree to customer terms and conditions.


Trigger Guard


Upper Receiver

M-4 mil-spec, stripped

Hand Guard

15 inches, with M-LOK mounting system


The U.S. Arms Company M4 Builder Set is manufactured to ISO-9001 standards to ensure the highest quality control and materials. This AR-15 receiver kit includes:

The Cam-Lock Builder Set can be configured with a black anodize or a multitude of Cerakote options for the hand guard, trigger guard and receiver set. This receiver set comes with our patented “Cam Lock” lower receiver so that you get the tightest receiver fit on the market, which gives us the confidence to claim that we are “Home of the World’s Tightest Receivers”. The Cam Lock lower receiver will also fit any mil-spec upper assembly.

Our builder sets are available in multiple colors and long lasting finishes based on your specific preferences and receiver choice:

  • Cerakote Battle-Worn Bronze
  • Cerakote Bronze Black Green Camo
  • Cerakote Alpine Dark
  • Cerakote Gun Metal Gray
  • Cerakote Bazooka Green
  • Cerakote Black Gray Camo
  • Cerakote Absolute Black
  • Cerakote Hot Chocolate
  • Cerakote Battle-Worn Titanium
  • Anodized Black

The U.S. Arms Builders set allows for better performance out of your AR-15 that’s custom to your preferences. With easy component replacement, creating one of the most accurate firearms is simple and secure. This builders set is also great for the first-time AR owner looking to get a better understanding of their firearm or for the seasoned enthusiast looking to add another custom AR-15 to the arsenal.

The U.S. Arms AR-15 upper and lower receiver set found in this builders set makes for the best custom AR-15. This weapon system was created to have a unique aesthetic, while giving the shooter the highest level of confidence and flawless performance in gun competitions, sport shooting, and defense for years to come.


Note: Cerakote items may require up to 2 weeks processing time.

(Complete rifles shown in photos are for illustrative purposes only. Only the parts listed above are included.)