I don't understand why it would be a no-no to put select fire components in an AR15 lower, as it is physically impossible to put a M-16 auto sear (require for full auto) in an AR-15. The sear pocket on the ARs is more narrow specifically to prevent installation of the sear. One could always use a DIAS, but that is a different story. Generally, logic would tell you that w/ a AR lower (as opposed to an M-16 lower), the select fire components would be fine as an essential component for their full-auto operation would be physically impossible to install, but who knows what the BATF thinks . . .

 

I think the general view of ATF is an AR-15 plus a single F/A component is a no-go. There was much drama for a time over whether a F/A capable carrier was allowed, and that seems to be resolved in favor of permitting "original" style carriers. Having F/A fire control parts...I wouldn't do it. My understanding is putting the full-auto pieces in an AR can result in the hammer following the carrier up and slam-firing, thus giving you a very unreliable but clearly illegal weapon. Since a hammer with a notch has to catch the full auto sear maybe that is different, but a full auto selector, connecter, and trigger seem to have great potential for getting you into serious levels of felony trouble.

 

You could have the same argument with a full auto Hk trigger pack, if the pack is cut to fit a semi shelf...also a no no, but the gun club I am part of has a SOT and made some post samples by simply fitting the pack to fit the shelf. Either way...both are allowed as long as you are in the law.

 

I believe the original question should be asked another way, namely why wouldn't it be allowed? Can anyone provide any documented proof that a FA hammer is not allowed in an AR type lower? Not "I heard", but a real ATF opinion. As noted, FA carriers are apparently allowed in ARs and some AR manufacturers sell their guns with a FA carrier. With either, or even both, the guns are still incapable of full auto fire.

Also, since the MR comes that way, no one can claim "constructive possession" like they might if you bought a gun with semi only parts and have a separate stash of FA parts. I don't see any issues with the MR hammer. I'm sure it's legal and HK knows enough to not sell a gun with illegal parts in the US.

 

Here is the thread I was looking for. The long and the short of it is that you can have F/A parts installed in an AR-15 -- as long as it doesn't fire in F/A. Beyond that, ATF "advises" against M-16 parts, and then things get pretty complicated. The legality of an M16 part in your AR- the short version. - AR15.COM

 

Wow. Very helpful. Thanks a bunch.

On a related note, I am working with a lawyer to get BATF to opine to whether I can have FA FCG in my lowers since I was under the same Internet lore that removing a RDIAS means having to remove the FA FCG. This makes moving the RDIAS from one lower to a different lower a PITA and not feasible for practical purposes.

I will forward this letter to my NFA attorney so that he can reference it as a starting point.

The first NFA lawyer I spoke to wanted to charge me $2K IIRC for just a federal opinion. And charge me extra for State opinion since I am allergic to jail (don't want to comply with Federal law but somehow be in violation of state law).

If I do get a formal BATF opinion, will check with my lawyer if I can share with folks here. Assume possible, but I have learned that my assumptions are not always correct...

 

I seem to remember, years ago, ATF issued a "bulletin" that listed and illustrated six specific auto fire control parts, any one of which was a no-no in a semi AR-15. It's an old memory, and I didn't have an AR-15 at that time, so I didn't pay a lot of attention. Auto fire control parts is one thing that can get you in trouble with a DIAS. As I understand it, you can't move the DIAS from gun to gun, while leaving in prohibited auto control parts in multiple rifles. Another thing that can get you in trouble is, making analogies between rules for AR-15s and HKs. Two different animals.

Who knows what ATF would say today, or tomorrow, or...

 

Hammer, disconnector, trigger and selector are all different between select-fire and semi-auto only. Now that I think about it, the MR556 disconnector is shaped to work with a select-fire selector. Here's a pic of the disconnector:


At one time, folks were rather hesitant to use a full-auto carrier in their guns, but that has obviously changed. But I still contest that FA fire control groups are something I would be very wary of putting in an AR lower whether it has a sear block or out of spec dimensions.

NOTE: Check out anywhere the Geissele SSF is sold and see the "NFA rules apply" warning.

 

Might this have something to do with the fact that they consider the upper to be the firearm with HKs but the lower to be the firearm with ARs?

 

The lower is the "firearm" on the MR series, like other ARs, but unlike other HKs. Otherwise, you wouldn't be able to buy complete uppers direct from HK.

 

No, you cannot legally.

 

my guess is because 416 carrier can't be use in 556 so to save few bucks, BATF okays for HK to use it. Also Piston AR carrier are specific to each model not likely to interchange with others. But DI AR is different story.

 

It is so silly that they don't want certain FA parts in any gun especially an AR15 type gun when that part alone cannot make a gun go auto.

Funny thing is if you have a regular plain style semi fire control group in an AR you can make it full auto no matter what carrier is in it (including the silly one with the bottom completely removed in the rear of the carrier) just by throwing in one metal part and not making any mods to the gun and removes in seconds. I cannot believe no one has figured it out before or at least not talked about it. I don't get why they care if a carrier can trip a sear or a disconnector or hammer work in FA when there is a way that is so much easier to convert one than adding some type of sear or lightning link or whatever.

They should just prosecute the people that make illegal full autos and not worry whats inside of a gun that doesn't run full auto. just my opinion.

 

I assume you are referring to a lightning link? No thank you very much.

 

You absolutely can have FA parts installed in a semi auto as long as they do not readily enable the weapon to shoot, automatically, more than one shot... FA bolt carrier, no problem. FA hammer, no problem. It's when you start modifying the lower receiver in an AR to accept the complete function of those parts that you get in trouble.

I have some late 60's era, Colt hard chromed FA bolt carriers in several of my AR's. Makes it a LOT easier during clean up time! But it does not allow the ready conversion to full auto and the rifles simply cannot fire in FA with just the carrier. I have had at least 6 compliance inspections in which these exact rifles in this exact configuration have been identified and been determined to be a non issue.

 

Thanks for the clarification. In the spirit of good discussion, how does this affect those with older guns like the Colt "green label" and other pre-bans with internal dimensions not specifically designed to not accept a sear?...At what point does constructive intent come into play?

 

That's a good question. I'm not sure where the bright line is for "readily." ATF takes the approach: "Any part designed and intended solely and exclusively to convert a weapon into a machine gun." But that really doesn't give you precision. A good lawyer would say that if it doesn't shoot full auto with the parts and is not readily (easily) modified to do so, then you are okay.

 

I'm confused. The part that you link to above is a hammer for a 416 not a MR556. To me installing full auto parts in a semi auto would come down to intent to a "reasonable person". If you don't have a conversion device, why would you install full auto fire control parts in a semi auto? There is no performance enhancement. So why would you do it?

With a full auto trigger, disconnector, and selector in a semi auto, IMHO you would have an unregistered machinegun. Why, because with the selector in the auto position, there is no disconnector function. So the hammer will follow the carrier back into battery. This could cause a slam fire condition which would meet the definition of machinegun. YMMV.

Scott

 

I'm confused. The part that you link to above is a hammer for a 416 not a MR556.

Scott

Nope, it's the same that's in the MR556 as well. Check out the pic of parts pulled from an MR556 lower. Notice the added little retainer deal; this hammer IS one that was meant to work with HK's proprietary hammer/trigger pins AS WELL AS the 2-piece trigger assembly that comes standard in the MR556.


And FYI, guys, I know how this s#!t works...BTDT. My question is legal/ATF oriented so save the 10-cent armorer lecture

 

The only issue at hand is: will the presence of full auto parts render the weapon readily convertible to full auto fire? It's sort of like having a three position selector and housing on a semi-auto HK MP5... It looks cool, and they certainly are full auto parts, but they do not allow for ready conversion to a machine gun. So no problem. And like my hard chromed, full auto bolt carrier... it does not readily enable full auto fire. But it DOES make cleaning a lot easier!

 

You sure that's definitive, SG?

I remember back in the late 70's/early 80's the ATF was able to get a Colt AR-15 to double and triple a couple times when M-16 parts were used in an AR-15. Did it double or triple reliably? NO... but that was the basis for the early charts showing what the differences between AR's and M-16's internal parts and the big bugaboo about M-16 parts in AR's. The fact that they could make it double or triple without the happy switch being drilled or installed as led to 30 some odd years of cornfusion.

Personally, it would make life for me a lot easier if I could use M-16 internals in ALL my AR guns. I'd like to feel a bit more comfortable about it, though.