We have received our classification letter from the BATF, confirming that our lowers are NOT considered a firearm.

How do you make an 80% into a 100%?

It’s easier than you might think.

There is a plethora of information out there on doing this. Everyone has a different way. It’s up to you. But here are the features that need to be added.


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What tools will I need?

You will need a vertical drill press, such as this one from Harbor Freight for about $70.


You will also need a basic caliper, some WD-40, some tape, several mill and drill bits to cut the holes and slots. You can get them from MSC or McMaster-Carr: Spend a little more and get some good quality bits. 3″ long minimum, longer is better depending on whether you have an R8 type collet, a key chuck, and the size / depth of the chuck. Buy extras, just in case.

  • High-Speed Steel Jobbers’ Drill Bit 1/8″
  • High-Speed Steel Two-Flute End Mill 5/16″ Mill Dia
  • High-Speed Steel Two-Flute End Mill, 3/8″ Mill Dia
  • High-Speed-Steel Jobbers’ Drill Bit, 5/32″
  • High-Speed-Steel Jobbers’ Drill Bit, 3/8″, 5″ L Overall



Here are the DIY steps using our own drill and mill jig

We have had lots of customers asking “How hard is it to do?” Well, here are the  basic steps. Not so hard.

We will emailyou a link to the most up to date version of our manual, with your payment receipt. It is in PDF form for download and viewing. We do not print a paper version to ship with the jig. If you would like to see a copy before you buy the jig, you can request one at sales@datumgear.com.

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Step 8

Do I need BATF permission?

Well, we cannot give legal advice, of course. But you can read for yourself the BATF regulations concerning making your own firearms here.

A screen shot of this regulation taken 4/26/2013 is shown below. Please check regulations for your own situation, and your local laws. 



Our assembly instructions are a general overview, and are not meant to take the place of a certified gunsmith or proper training. They are for informational purposes only. For more details on the various ins and outs of gunsmithing, we recommend the NRA Gunsmithing Guide, available at Amazon.com and other retailers



ASSEMBLY TIP FOR UPPER RECEIVERS: when you install your barrel nut onto your upper, you will need to hold the upper receiver firmly while you torque the combo wrench. You might be able to use a some scrap materials around your workshop to help avoid marring the receiver’s finish in your vise. OR….if you happen to have our handy-dandy Drill and Mill Jig (#1600-15J), you already have the solution in your hands! Just add a 1/2″ minimum thickness piece of wood, metal or plastic, and you have a dandy upper receiver vise block. Check out the pic.




TECH TIP: having some trouble pushing your gas tube through the clover-shaped hole in the front of your receiver? First, double check your barrel nut and make sure the holes are EXACTLY lined up. Do NOT force the gas tube and for Pete’s sake, do NOT use a hammer. It should slide in easily. If your holes are all lined up and you still cannot get the bulbous end to fit smoothly, double check the diameter of the receiver hole. You may need to chase it with a file (one of those rat-tail files from Harbor Freight work fine) a little at a time until it just fits. Work your way around the hole with the file on all 4 corners evenly to ensure it stay circular.


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