Wednesday, November 17, 2010

Some Final Notes On The Colfax Tactical AR-15 Project

Of course, I've written several pieces on the AR-15 project which consumed a few weekends of my time.  My point in writing this is to add a few notes and make a perma-link posting over on the right side bar, so that the articles are available and relatively easy to find for as long as this blog is here.

First off:  this is not a difficult project.  There's not much in the way of tools needed to turn an 80% lower into a ready to build lower receiver.  In no particular order:
  • Drill bits in 1/8, 5/32, 5/16 and 3/8"
  • A decent set of calipers.  Digital calipers are cheap nowadays.  
  • A bit of a trick here:  either a drill press or a milling machine.  There are many "Mill-drills" (example) on the market which can do this, but an 8" benchtop drill press (for example) will do. If you don't have a drill press, they are just so handy for any wood or metal working that, honestly, use any excuse you need to get one.  I used my CNC Sherline because it's what I had - wouldn't you? 
  • An end mill:  3/8" is a common shank size, almost universal, and will work fine.  A smaller mill takes longer to clean up the insides.  I believe the largest you can use is 7/16".  End mills are available in a center cutting styles, but won't be unless stated.  An end mill is not a drill, but a center-cutting endmill works better for small amounts of drilling than the other kind.  If you use a milling machine, you'll use an end mill holder or collet; on a drill, you'll use the drill's chuck.
  • Most of the lower is 1.249 deep, but there's a "shelf" near the butt stock end that is 0.63" deep.  
  • The Colfax lower comes with a CD Rom that has several worthwhile drawings.  You can find almost all of them online separately, but it's handy to have them in one place.  
  • A fixture: either the one Colfax Tactical sells or the one from CNC Guns. This clip, modified from the instructions will help. 

Once you have the lower hollowed out, it is pretty simple to add all the parts to make it functional.  Parts kits are widely available, and instructions are, too.  At this point, there are some tools you may want that you'd need if you did not finish the lower receiver, like any other AR project - I leave that up to you.  I had never done it before, but finished the lower in an hour or so - going back and forth between this computer (watching a DVD) and the garage, after every major step. 

Finally, there's more than one way to do this.  If you get a different lower with instructions and they recommend different tools, listen to them, not me!  They may have a different set of holes and cuts defined to make their "80%".  

It's easy, it's fun, and you end up with a rifle.  What could be better?  As always, you can email the blog account or comment here with other questions. 


  1. Thanks for sharing your experience. Its very thoughtful of you to put it all together in one place like this. I'm gonna bookmark this for later... =)

  2. Glad to help.

    I suppose the savings in dollars is not terribly large, but without a direct comparison model number from DPMS, I'm guessing I saved about $200. That's not the main reason for doing this project. The main reason was "because it's there".

  3. I know what you mean. I tend to do a lot of things the hard way that are of questionable benefit. Of course I can reason that it might save some money or be better than what you can buy or what have you. But the real reason is "because I can."