Planning to build a rifle utilizing Brownell's A1 retro lower and a 70's era colt upper (w/ Colt bolt group) plus trap door stock group. I can pick up a complete colt lower parts kit as well - but should I?  Obviously I wouldn't have the full auto sear or the proper machining in the Brownell lower but in reading (including the AR15.com article about tell full auto parts from semi-auto as well as the ATF's PDF) it seems that even having the M16 hammer, trigger and fire control could make it illegal.  Am I interpreting that correctly?  Can I use the trigger group and fire control for cosmetic reasons but use semi-auto parts for the rest and be legal?  Any help appreciated.

M16 parts in a semi auto receiver are meaningless, just like an M2 slide, and sear in an M1 carbine are meaningless.  Years ago, when I was an FFL dealing in LOTS of ARs and M16 stuff, I talked to a BATF agent that I knew.  As far as Federal law goes, if the parts can be used in semi-auto also, and not cause it to be full automatic, it is legal.

The reason possessing an M16 hammer, selector, disconnector and trigger is not illegal is that they need a full auto receiver to make a machine gun. That is why BATFE allowed the M16A1 kits  to be sold and built into semi auto kits.

The reason a complete set of M2 Carbine parts is considered a machine gun, is they can go in any M1 carbine, regardless of receiver and make it a machine gun.  As I said before, however, just an M2 disconnector and M2 hammer in an M1 Carbine are OK.

Use the original parts but have them "converted" do the specs of semi auto fire control parts.

calguns.net

You will get better info there for remaining not just
Federally compliant. But also California compliant.


As for an FA parts... Hammer.... just don't.
Unless you cut off the sear trip.

Just get a found anywhere " quality " lower parts kit and  you will not need to cut a FA Hammer.

FA carriers seem fine to use even in Commiefornia.


Remember. Besides ATF
You have CADOJ to screw you too.

FlowJoe:

You are correct--BATFE views any M16 parts in a semi-automatic receiver as "constructive intent" even tho' it's utter nonsense. They explain on their web site.

If you grind the spur off the top of the M16 hammer, you can use it.

If you cut or grind the rat-tail off the disconnector, you can use it.

If you weld the open rear area of the trigger so a select fire disconnector cannot fit, you can use it.

The selector switch cannot be used unless unless you weld/fill the portion that would engage the tail on the disconnector.

As a result, it's easier to just use a semi-auto trigger, hammer, disconnector & safety/selector.

Now--unless you do something stupid, the likelihood of a cop or ATFE agent seeing the parts is unlikely....but lawyers are about $400-500/ hour. The LPK is waaaay cheaper. But, you make your choices & take your chances.

Not really meaningless, with selector in auto the gun will slam fire with m16 fcg, or the use of a dias it will run in auto.and that agency can change there mind any time on whats legal and whats not.OP i say convert to semi or sell and buy a sp1/sp2 fcg.

Thank you for the responses all.  I do belong to calguns as well and have been reading there too.  Had to start somewhere and figured I'd work on federal compliance first.  This article was really helpful https://www.ar15.com/content/legal/AR15-M16Parts/ but also led to me making this post for clarification of the finer points.

I had also read that having FA parts inside could lead to "accidental" auto bursts (even without the FA sear) which would certainly tell everyone what's inside..

ATF has been known to screw with confiscated ARs containing some M16 parts until they got them to slam-fire, then bust their owners for possessing a machine gun. There was a guy in WA state who found that out the hard way many years ago: http://keepandbeararms.com/information/XcIBViewItem.asp?id=1123

An AR with all M16 parts, but no sear, can still slam fire, particularly if you use commercial ammunition which has a more sensitive primer than military surplus ammunition.  Happened to my brother-in-law.  It fired about 10 rounds before jamming.  We then converted all the parts to the semi configuration.

Reading stuff like this just makes me mad. Situations like this are the reason we have the 2nd amendment!