cc-settings-icon BUILD AT HOME
80% Arms sells AR-15 and .308 80% Lower Receivers, 80% Lower Jigs and other accessories which allow you to legally build a firearm at home in most states.
We utilize state of the art 5-axis CNC machines to mill all our .308 and AR-15 80 percent lower receivers to incredibly precise tolerances using premium billet aluminum.
We also offer our patented AR-15 and .308 Easy Jigs® which is the first 80% lower jig that makes it ridiculously easy for a non-machinist to finish their 80% lower in under 1 hour with no drill press required.
Products manufactured by 80% Arms carry a lifetime warranty against manufacturing defects. We will promptly replace or repair any product that we determine to be defective.

M4 Upper Receivers

What is an M4 Upper Receiver?

The M4 emerged in 1984 and was officially adopted by the US military in 1991. Since then, it's earned a revered place in the heart of every gun-enthusiast as one of the most formidable combat rifles of all time. The M4 had a few distinctive features, like it's barrel-cut for an M203 grenade launcher, as well as it's vastly improved feed-ramps. Chances are that if someone is referring to an "M4 Upper Receiver" nowadays, they're probably talking specifically about it's feed-ramps. As technology has advanced in the AR-15 platform, people are no longer running the dated M4 barrels and hand guards. 

Are M4 and AR15 Upper Receivers the Same?

Yes. They are virtually the same thing as they will work with “M4” or AR15 parts interchangeably. The difference between M4’s and AR15’s lies in the lower receiver, not the upper.

M4 Upper Receiver Feed Ramps

The M4’s feed ramps were developed to rectify full-auto feeding failures once the weapon starts to get dirty. Previously, feed ramps only existed inside the barrel extension, and the M4 Upper sought to modify that for improved reliability. By widening, and deepening, the feed ramps of the barrel extension, and extending them down the upper receiver to where the lip of a magazine sits, it removed the issue of rounds hanging up when feeding into a dirty gun. Largely any AR-15 Upper Receiver on the market to day is going to have the M4 feed-ramps, as a vast improvement with no downside.