Project 6 - Scratchbuilt AR15 receiver

This project is the construction of an AR15 receiver completely from scratch and entirely on a tabletop mill.

Please read the disclaimer on the main page and note that I am not a lawyer. According to US Federal law, it is legal for a private individual not otherwise prohibited from owning a firearm in the US to build their own firearm. The firearm must be a Title I firearm as outlined in the National Firearms Act of 1934 (among other things, no automatic firearms, no sound suppressors, etc.). That still leaves a very broad array of firearms that can be made by citizens. A serial number is not necessary as this firearm is made by a private individual for personal use - it cannot be made with the "intent" to sell it. The BATF recommends that the private builder put a serial number, but it is not required by US Federal law. Only licensed manufacturers (i.e. holder of a Type 07 or Type 10 Federal Firearms License) are required by law to put a serial number on their manufactured firearms. Note that the under US Federal law, the "receiver" is the part that is considered the actual "firearm" - other parts like the trigger group, barrel, bolt, etc. are just pieces of metal.

State law varies in the US, but private gunmaking by citizens is legal in most US states. It is the responsibility of the reader to check for himself. Some states may require a serial number.

A company The Tannery Shop Inc is offering a BATF-legal 80% complete AR15 receiver. The BATF has ruled that 80% complete is not a firearm (its just a piece of metal) and can be bought/sold without paperwork. A private individual can then legally finish the receiver for personal use. Note that the final owner/user must be the one to finish the receiver - the work cannot be contracted out to others. Quite a few individuals have finished their own legal AR15's in this way.

I thought of trying the 80% complete receiver route, but felt that if I could build an AR15 receiver from scratch on a small mill, it would make a very interesting project. An AR15 receiver is too large to machine from a solid block on a small tabletop mill. Machining the magazine well is going to be terribly difficult if not impossible and there is not enough room to bore the hole for the buffer tube. In addition, a suitably large block of aluminum will cost around $50 and making the receiver from a block will generate a lot of machining waste.

The receiver is made of several parts bolted together. This makes it much easier to machine on a tabletop sized mill. Another advantage of machining it in pieces is that the design is can be easily changed to have magazine well sizes for other chamberings like 9x19mm. It is also possible to experiment with different materials like Delrin for lower stress areas like the magazine well sides. While a multi-piece receiver may not be as strong as a one piece unit, the AR15 receiver does not bear the brunt of the firing stresses. The barrel, barrel extension, bolt and bolt carrier are the parts that see the most stress - these parts are purchased off-the-shelf. I have no plans to machine and rifle my own barrel (well not yet, anyway ;) ;))

I started with the AR15 blueprints available for download on the website or I have simplified and "squared off" the design of the receiver and divided it into 10 parts that are bolted together with #6-32 button head and socket head cap screws. To keep things simple, I have modified the design as follows: The scratchbuilt receiver will take standard AR15 fire control parts and will have the standard magazine release button. I have done this project entirely on a tabletop mill and the most basic of milling machine accessories. I did not need a rotary table or other expensive fixtures. I did have to buy a boring head to bore the hole for the buffer tube (aka receiver extension).

Each piece is relatively easily machined on a table top mill. It just takes time. If the reader wants to use larger pieces of aluminum, the receiver can easily be built using fewer bolted pieces. Since each part in the current design is small, it is easy to find/buy aluminum stock to make the part - this keeps material costs low and minimizes machining waste. I was able to find all the aluminum (basically just aluminum plates and 4 small blocks) from a local scrapyard for around $7! The aluminum is mostly alloy 6061 which is not as strong as the alloy 7075-T6 aluminum used in a typical AR15 receiver, but it should be OK as I have beefed up certain areas.

After machining was completed, the pieces were degreased and bolted together. Loctite 242 ("blue") was used to hold the machine screws in place. "Rust-Oleum" flat black paint was used to finish the metal after a thorough sanding using a fine abrasive pad. I used a sponge brush to apply the paint. I recommend thinning the paint first since it is a bit too thick to apply smoothly (found out the hard way!) I put two thin coats of paint with a light sanding between coats. The finish will look "powdery" and almost gray after sanding. Wiping the finish with Breakfree CLP will give a decent uniform black finish. Some minor brush marks are still visible, but I can live with that. The 1/4"-24 bolts used to hold the rifle together instead of pushpins were painted as well. I thought of home anodizing it, but since the pieces are made from different aluminum stock, they may wind up with slightly different shades of black!

I bought an AR-15 carbine parts kit (everything except the lower receiver) from a gun show to complete the rifle. There are several sources of such kits. I got the plain barrel with no muzzle brake since I want the carbine to be as simple as possible.

I have made complete blueprints for the AR15 scratchbuilt receiver. They are available for free download as a single 935kbyte .pdf file. I do not have a high bandwidth server to host them, but fortunately, there are several copies on the web:
Blueprint Q&A
Some readers who are building the receiver had questions on some "missing" dimensions in the prints. Actually, all the dimensions are present but you may have to look at the dimensions of another part or sheet to figure it out. To make things clearer here are some questions and answers: Photos
I know you all want pictures so here are some of them. All these pictures are also stored in My Webshots Albums.
Please use the Webshots link to save bandwidth if you want to see all the photos (its faster too).

Parts-in-progress: Assembled Receiver: All Done:
Since posting this, quite a few readers had questions. Here are the answers....
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