Lets clarify one thing first… When we use the term M4, there are two possible interpretations:

  1. Reference to the specific M4 model / configuration of an AR-15 produced by Colt. This is a Colt model number and is NOT available to civilians. (Sad Trombone)
  2. The type of feed ramps cut into the upper receiver and barrel.  This post is dedicated to that concept.

Both upper receivers and barrels are available in an ‘M4’ design. What exactly is that?  Here’s what I can gather:  [click this post to expand the article]

Your barrel extension (the part that fits in your Upper Receiver)  already has feed ramps built into it.  When the bolt pushes a new round towards the chamber, the bullet tip hits the feed ramp and gets guided into the chamber. Pretty simple.

M4 Feed Ramps take the standard feed ramps to the next level . M4 style ramps extend beyond the end of your barrel extension, and continue this deeper cut through your upper receiver.  By extended the feed ramps even further, you can help eliminate possible feeding problems.

How so?  Lets say the spring in your magazine is going bad, and after you fire a chambered round, the new round in the magazine hasn’t quite made it all the way to the absolute top of the magazine before being slammed forward by the bolt.  Or, maybe the round is faulty and the bullet projectile is not centered.  It is possible a non-M4 design might jam, where the M4 feed ramp would catch the tip of your bullet, and help guide it into the chamber.  Yes, another example in your life where ‘just the tip’ helps you survive.

So do I need M4 feed ramps???  Honestly, nope.

A lot of AR15 components come with M4 feed ramps as a standard.  BUT, you do need to pay attention to the parts that you’re ordering.  Your Upper and your Barrel Extension SHOULD match.  They don’t HAVE to, I’ll explain.  Below is a diagram courtesy of ar15barrels.com.

Lets talk about the lower left corner of the diagram.  If you pay ZERO attention to what you’re buying / assembling, there’s a 25% chance you’ll configure a pretty dumb idea.  What’s happened in this scenario is that a NON-M4 barrel is installed into an M4 Upper Receiver.  If a round starts to feed and hits the M4 ramp on the Upper, it will MOST CERTAINLY jam when it its the lip of the barrel extension.  Don’t set yourself up for disaster, avoid this configuration.