Finishing 80% Lower Receivers

We have two separate discussions here, and the beginnings of a third.

My understanding (as a layman, and this is not legal advice is):

  • making an 80% receiver has no legal ramifications at all — it’s simply a chunk of metal in a special shape — one could sell them as ash trays and they would be completely legal anywhere in the U.S.
  • finishing an 80% receiver is legal for anyone who is legally able to own a firearm both where they do the work, and where their legal home of record is
  • the specific law on sale is that the firearm cannot have been made with the intention of selling it, but that if it was made without such intent, it would be legal to sell later — however the BATF has closed this “loophole” by aggressively pursuing this “thoughtcrime” and at this time, it looks like the only way to legally transfer a self-made firearm receiver is to make it part of one’s estate, which is the only legal transfer of firearms which is not considered a sale (trading/gifting falls under the same regulations/guidance from the BATF)
  • the sear mentioned above is a different thing, it is the key to making a weapon full auto (or with a suitable control group, selective fire) which is a Class III item, and requires paperwork and a tax stamp, which is illegal for anyone to own without having filed said paperwork and gotten approval (requires a background check) and for new manufacture, requires that one meet certain requirements for destination and intent and so forth including having an FFL w/ Class III certification. It is not legal for individuals to own Class III items made after a certain date. Interestingly, felons are exempt from this, since their filing the tax paperwork has been ruled to qualify as “self-incrimination”, which I believe is the ultimate statement on how Byzantine firearms laws have become.

I hope that this frames our understanding of the legality of this thread adequately — to expand on this, we will of course expect that receivers are marked with only two positions — the need for such checks is a further example of why we do not wish to host files (but will accept images and instructions which are clear enough for folks to make their own files from scratch).

Lastly, I will note that some folks have flagged this thread — anyone who doesn’t like firearms should simply skip past it — hopefully we can go back to actual content on the mechanics of finishing receivers and so forth.


I am more interested in the work-holding fixture than the actual project.
Both items look like the work of someone who knows what they are doing and how to craft pretty decent product.


Haha, thanks. That was my intent for posting this. I’ll pass your complements on to CM-Tactical in case they haven’t been following the thread closely.


@WillAdams Exactly. A lot of folks think our constitution enables them to make whatever they want whenever they want to, and that is simply not the case. I would urge aspiring gunsmiths to do their due diligence and find out what’s legal in their particular locales. Hopefully by then they’ve already done whatever soul-searching they need to do, since firearms are still dangerous once they leave our hands and/or our shops.

On a totally separate point, folks who are interested in marksmanship or sport aren’t much interested in the AR. It pretty much has exactly one purpose, which is fun for a mag or two until you have to scrape carbon off the bolt carrier with dental tools. Lower receivers have a kind of low bar for entry, but actual gunsmiths are lathe guys.


Wise words indeed. Also, a gentle reminder that less than 5 out of 100 people have these particular 2nd amendment rights, and the laws about firearms are often drastically different for the majority. So, yes, check locally and know where you stand.

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:crazy_face: That has to be nuts. It is likely that it would bring the additional charge of tax evasion in the UK. :grin:

I like seeing the many and varied uses to which people are putting their machines. I could not begin to imagine or predict the aspects of paperwork, thought crime, actual criminality and government oversight of this type of project in the UK.

I own and use compound bows along with 10 metre air pistols and rifles. There is an order of magnitude difference from firearms ownership and use in the UK, when compared with the USA. We appear to have several laws and regulations that include acts preparatory to the commission of a crime. This is one possible/probable conclusion to an official line which would deem making an 80% lower unlikely to fly, unless one has a licence to manufacture a gun.

Again, we’re veering off into politics, but for cartridge semi-automatic and repeating and single shot long-arms, one simply needs to be 18 years of age, not a felon, not convicted of a domestic violence charge, and live in a locale where the particular weapon is legal (magazine capacity, &c.), and cartridge semi-automatic pistols, revolvers, and single shot pistols simply raise the age to 21.

More importantly, even if one limits firearms to the members of the militia called out in the Second Amendment as the raison d’être that is: 10 U.S. Code § 246 - Militia: composition and classes | U.S. Code | US Law | LII / Legal Information Institute

The militia of the United States consists of all able-bodied males at least 17 years of age and, except as provided in section 313 of title 32, under 45 years of age who are, or who have made a declaration of intention to become, citizens of the United States and of female citizens of the United States who are members of the National Guard.

which is better than some 45 million: • U.S. population by age and gender 2019 | Statista and a bit more than 5% and not being a chauvinist Constitutionalist would more than double it.

Calculating how many folks live in locales where firearms ownership is strictly limited is left as an exercise to the reader — but all such folks have the freedom to move (or at least buy property in some locale where ownership is not so limited), so by my count, have the freedom to keep and bear arms, should they choose to exercise it.


I don’t know if you intended to reply to me, Will. I’m not sure it follows what I was wrote, which was reminding people that the rights you are all quoting here are US-specific, and only directly apply to less than 5 out of 100 people (in the world).


That the rest of the world has to make requests such as:

is in the realm of politics and off-topic here.

Nice article… but I think you are the only one that’s mentioned politics in this thread :wink:


Interestingly, 40% of the members of U.S. Law Enforcement have been CONVICTED on Domestic Violence charges, but are provided with Government Issued firearms…
just thought I would throw that in there for thinking on


And now we’re off on to politics. That merits further research and discussion which folks are encouraged to do somewhere else.

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To jump away from politics…

That’s a great idea. We’ve been asked for years if it’s possible to finish an 80% AR15 on a Shapeoko and we’ve always said, “not really”. It never occurred to us to mount a fixture off the front for a lower. Well done.


I’m not sure if I captured all the info on the video, but what I do see is a video on how to modify a part, some pocketing, work holding, and nothing technical that I remember, so no technical drawings illustrating dimensions or tolerances that would be needed, nothing more than a general workflow with techniques showing the abilities of the machine. I’m not an advocate for weapons, but I do see value in using them for hunting, law enforcement, military and competitions. My grandfather used a pistol in marksmanship competitions, locked it up and kept his ammunition at the shooting range and only for those purposes. I have only shot a .22 rifle, pellet and bb guns. I personally don’t find the experience of shooting exhilarating or interesting as it feels to me like using a railgun, it is just a tool. To each their own. Fishing, on the other hand…

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I have a design that I just need an excuse to make that adds a vertical table with pretty decent rigidity. I designed it for my SMW fixture plate though. It wouldn’t be as easy to use or as rigid on an MDF table. I have always wanted to see if I could finish a lower on my machine, I may just have to make it. If I do, I will post pictures.


Just an update… I promised to post another video that is more instructional for using this fixture, but I have been traveling for the last month and been unable to complete the editing. I thought I had enough video with me on my computer to put together an instructional, but I have found that I am missing a couple of key shots that need to be included.
I’m not sure when I will get back to my machine to get these shots, so I have reached out to a friend to see if I can obtain them that way. I’ll post something as soon as I am able to fill in the gaps. If I can’t successfully fill the gaps in the short term, I will try to edit it in a way that I capture most of the process and get that posted (assuming I can make it flow together properly!).


Just curious if there is an update to the availability of the tooling.

Hi Jimmie,

As to the tooling availability from CM-Tactical, I recently communicated with them and learned that they are having difficulty getting the attention of a suitable machine shop for production. Everyone seems to be tied up with orders from High Tech Companies, and these are going to be small enough volume that no one seems to want to mess with them. Talks and negotiations are ongoing…

They have kicked around the idea of producing these on the Shapeoko itself, but the throughput is significantly low and the finish quality may not be up to the expectations of the potential buyers. They may end up having to pursue that path if a suitable shop can’t be located.

I’ll try to post on this site with any updates if the topic is still open. Otherwise I’ll start another topic for the updates.


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