More Homemade AR-15 Lowers

Jason sent this link along to me yesterday, which shows another AR-15 lower design that someone came up with. Looks pretty simple, and definitely wouldn’t take all that much machining. The only thing that concerns me about deviating seriously from the standard AR design is whether an argument could be made it’s readily convertible to an M16 receiver. I believe AR-15 lowers have some extra metal in them to prevent insertion of a drop-in auto sear (DIAS). They also have the advantage of having been reviewed by ATF. I’ve heard ATF frowns on designs where conversion is just a matter of drilling a new hole. But I also believe (correct me if I’m wrong) that once you drill the holes for the AR-15 trigger group, being that they’re differently sized pins, it essentially won’t hold an M16 trigger group anymore, so that really no modern AR design can really be construed to be readily convertible. I’m wondering whether there should be any concern about a design that hasn’t been submitted to ATF in order to make a determination. Any comments?

I should also note that this is only a concern for people, like you and me, who don’t want to break the law. Criminals wouldn’t have any such compunction.

6 thoughts on “More Homemade AR-15 Lowers”

  1. If these DIY receivers are not marketed for resale, I don’t think it should matter.

    There’s a couple local AR receiver manufacturers in my area. I had one ask me if there was a serial number preference (within a range of course), in case I wanted a lucky sequence of digits, etc.

    You get very different perspectives on these subjects based on where you ask :)

  2. There are plenty of commercial lowers that can take a drop-in auto sear, they are called “low shelf” lowers, and there’s nothing illegal about owning one.

    With respect to the pins, AR-15 pins are the same diameter as M16 pins. What you may be thinking of is Colt selling guns with pins that were larger than standard. They also for a time sold guns with a sear block in the lower, a bridge between the left and right lower walls that physically occupied the place the auto sear would be.

  3. The standard diameter for M16 FCG pins and AR15 FCG pins is the same. Only Colt has used slightly larger pins, and IIRC even they’ve gone back to the standard in the past couple years.

    As for autosears, you’ve got three different common possibilities:

    1. AR15 receiver with a high shelf (the flat part under the selector). This won’t allow a DIAS to fit.

    2. AR15 receiver with a low shelf. This allows enough room for the body of the DIAS to fit between the rear lug on the upper and the shelf on the lower. This is just as legal as a high-shelf lower; different manufacturers just choose to use high or low shelf lowers. I think upper to lower fit will probably be better, on average with a high shelf lower.

    3. M16 lower with no shelf and a third pin hole for the auto sear. An M16 has even less metal under the selector. AFAIK it has no legal significance. The presence of the third pin hole is the sole determining factor as to whether an AR-family lower is a machine gun or not.

  4. hmmm, that’s a pretty nifty design. It looks as though the magwell is held on via screws. That means that the magwell could be changed, much like the MGI Hydra. AR-15 with grease gun mags anyone?

  5. I’d like to design a 1911 in a similar way. I have the blueprints for the 1911, but I haven’t yet figured out how I would do such a thing. I’d basically like to be able to manufacture lots of reliable guns, reliably and cheaply, in the event of a major war or a revolution.

    I’ve also had two legal questions I’d like to explore at some point. First, what would be the legal status of a fully-automatic upper that can be operated soley on a strictly-semiautomatic lower? An upper isn’t a gun, so it can’t be a machine gun, right?

    And second, what about black-powder machine guns? Would they be legal, so long as you had to load the magazine by hand? Would the magazine have to remain a part of the gun to be legal, or could you make it detachable? (The design I have in mind would be similar to black-powder revolvers–no shells, so you have to pack the magazine every time you shoot it.)

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