Is there an ATF guideline of what to modify for semi-auto use? I looked around here but couldn't find anything that wasn't five or more years old on the topic.

I have bought an M16 LPK for all the correct retro parts and proof marks, what do I need to modify before I assemble it in an AR15 receiver?

Thanks.

Some say you can use the safety, some say you can't.

I do know that you have to grind off some metal off the trigger.

It is o.k. to use the M16 bolt carrier group, but it is wise to modify the hammer, disconnector and selector to a semi-auto function.
There are areas to grind away so the parts no longer interact as automatic parts.

I will find the FAQ that shows the parts (M16 vs AR15) side by side....
Here ya go :)
http://www.ar15.com/content/legal/AR15-M16Parts/

You shouldn't use the FA disconnector, you have to dremel off the shark fin on the auto position of the safety, grind/dremel the hook off the hammer, and some say you should fill in the rear of the trigger. As long as you use a semi auto disconnector and mod the rest of the parts, I've seen unmodified triggers in older 1980's Olympic, Sendra's and PWA's

ETA: Me personally, I won't use any FA FCG parts other than Modded Hammers and Modded Selectors, I'd do the samething if I were you, but if your hellbet on using more parts....please read up on this subject and listen to others who have much more experiance with using/modding the Triggers and Disconnectors. Also do your homework on all the legal mumbo jumbo, IMHO using FA Disco's and Triggers aren't worth the risk.

The law is that with a single trigger pull no more than 1 bullet may be fired.  

There is no law that says you can't use unmodified M16 parts with the exception of the auto sear.
If you have the auto sear(not shown in this picture) and don't have a registered MG then throw that part away.

This image shows where to modify by grinding off material, and adding to the trigger.

John Thomas at retroarmsworks.com can mod these for you to semi standard. He does a great job at a good price.

I used to have the ATF imfo on the puter
But I can't find it. Basically it stated that's it's ok to use FA
Parts as long as they are "neutered" to sp1 specs .

That said, I don't use them. The only thing I'll use is
The selector,  purely for looks. So the gun goes-
Safe/ semi/semi.

The ATF FAQ link no longer works. Is that ATF page still around?

Thanks for the info so far everyone. Keep it coming.

In the past word of mouth said that the mere possession of a m16 lpk in the same premises with an ar-15 lower receiver implied intent to convert and could invite prosecution. Not sure how the political winds blow now or if that was ever even a valid concern. I'm not a lawyer.

Perhaps it's now time for a tech branch letter?

ETA: Upon some searching and reading on the ATF website. Some thoughts.

MG:
The term ‘‘machinegun’’ means any weapon
which shoots, is designed to shoot, or can be
readily restored to shoot, automatically more
than one shot, without manual reloading, by a
single function of the trigger. The term shall
also include the frame or receiver of any such
weapon, any part designed and intended solely
and exclusively, or combination of parts designed
and intended, for use in converting a
weapon into a machinegun, and any combination
of parts from which a machinegun can be
assembled if such parts are in the possession or
under the control of a person.

So as long as my "combination of parts" (read: LPK) does not include the auto sear or auto sear pin, I would be theoretically good to go since it's not possible to make an M16 without those parts? Let alone a receiver not drilled for the pin?

Regardless, I think I am going to contact the FTB for an official letter rather than trust what I see out there on the internet. I'll update what I send.

Since I could not find a suitable answer, I decided to email the Firearms Tech Branch. Here is what I sent:

"Good Day,

I have a question regarding the usage of M16 Lower Receiver parts in an AR15 receiver. I have heard many schools of thought about what is legal/not legal to use so I thought I would write you for a final ruling.

According to 26 USC Chapter 53 § 5845 (b):

The term ‘‘machinegun’’ means any weapon
which shoots, is designed to shoot, or can be
readily restored to shoot, automatically more
than one shot, without manual reloading, by a
single function of the trigger. The term shall
also include the frame or receiver of any such
weapon, any part designed and intended solely
and exclusively, or combination of parts designed
and intended, for use in converting a
weapon into a machinegun, and any combination
of parts from which a machinegun can be
assembled if such parts are in the possession or
under the control of a person.

I am particularly looking at the bolded part.

My question is:

Assuming the Auto-Sear and Sear Pin are not in possession of the same person assembling the AR15 .If an AR15 receiver is assembled containing an M16 Hammer, Trigger, Disconnector, and Selector, but without the Auto-Sear or Sear Pin, would that firearm be in violation of the law since the above mentioned "combination of parts" is not able to cause more than one shot by a single function of the trigger? Again, this is assuming the Auto-Sear and Sear Pin are not in possession of the same person assembling the AR15, would the above firearm meet the definition of a machinegun?

If the above firearm would be in violation of the law, are there acceptable ways to build an AR15 receiver with M16 Lower Receiver parts" modified" to AR15 specification? Does the ATF have established guidelines for this? For clarification of "modified" please see the image I have attached below.



I thank you for your time and look forward to your answer on this issue.

Regards,

SGL_Shooter"

I will update when they respond. Hopefully this will set the standard instead of having to rely on internet hear-say.

someone here posted that they had called and asked the question when all the m16a1 parts kits came out and the response they got was that it was fine to use without modification as long as you didn't install the sear.

wish they would have gotten that in writing.  hope you do so it can be quoted for posterity.

ATF advises to modify full auto parts and that using them without altering may be illegal.

Using the parts unaltered is not illegal, but it increases the chance that may fire more than 1 shot with 1 trigger pull-which would be illegal.

You can not use a part that is solely for automatic operation and does not have a function in semi.


You won't get a yes or no type answer.  It's legal if only 1 shot per trigger pull, Illegal if more than 1.

ATF can't make law, only enforce it.  



http://www.ar15.com/forums/t_1_6/739614_The_legality_of_an_M16_part_in_your_AR__the_short_version_.html

M16 fire control parts in an AR15 are a no-go per ATF "ruling".  Info directly from the BATF:

"In order to avoid possible violations of the NFA, M16 hammers, triggers, disconnectors, selectors, and bolt carriers must not be used in AR15-type semi-automatic rifles, unless parts have been modified to AR15 Model SP1 configuration."

Notice they use the words: MUST not be used.  They do not say these parts SHOULD not be used.

Source (bottom center of page 1):  https://www.atf.gov/files/publications/newsletters/ffl/ffl-newsletter-1986-07.pdf

Please don't shoot the messenger... I understand the ATF's definition of a machinegun, I understand what manufacturers have done and currently do, and I understand the conflict.  But it is in writing, from the BATF, on what you must not do.  I'll do the simple thing and avoid testing them over $50 worth of parts.

John Thomas

I don't think asking one more time will hurt, getting their final ruling in writing in an FTB letter will only clear it all up for the future.

I do wish I had seen that while searching earlier, I couldn't find anything on the ATF site so that's why I wrote them.

That is advice, not law.

Okay.

 

This is not hard. Send them to JT to be modded, and done.

The M16 BCG is totally good to go...in fact its pretty much all you can buy from any vendor. The fire control group however is a no go. They are NOT going to tell you a M16 fcg is ok in a semi gun. Why? Because DIAS exist and could make it auto instantly. The whole intent of the law is that auto guns and ones that can be auto with a simple drop in part ARE NOT ALLOWED. you dont even have to think about it that hard to say, oh yeah. Right.

Mod the original M16 parts to sp1 config. Problem solved. You still have the look - the old ones do look different, and youre GTG. And it cant be auto with a drop in part thus making you free to enjoy it without fear of prosecution.