Just seeing how Lage uppers have completely transformed the MAC series of machineguns with 5.56 and potentially even belt feds in the future, could we see new hosts for other machineguns like HK sears? Would it be possible one day to get a HK sear into a Tommybuilt Tactical T36K for example?

ATF says no.

There's already the MGA SAW that'll accept the HK sear pack, but currently ATF only allows post-sample sears/packs to be used in them (because it's a different "family" of firearm than the HK9x series).

ATF has explicitly stated that the HK sear can only be used in the same family of weapons.  Same reason DIAS can be used in an AR-10

Yeah no, have to stick with roller lock HK's. The G36 is a completely different weapon system. Even though it's an HK, it's like comparing apples to oranges. However there's plenty of 5.56 roller guns. I love my HK-53 a lot!! And for 9mm it doesn't get any better than an Mp5.

It could be possible if the new mechanism is made to fit inside a roller locked receiver. The AR system has blowback, rotary delayed blowback, direct impingement, long and short stroke piston mechanisms in use. But a LL or DIAS would still be installed in an AR receiver. So as long as the new mechanism was installed in a roller locked style receiver, any firearm mechanism could be used.

Scott

What about FNC sears?  And are they still relatively inexpensive?

My personal take is that legally, a machinegun conversion device should be able to be used in any firearm that will accept that conversion device as long as the host receiver requires no modification and there are no other machinegun specific conversion parts required to enable the conversion device to function.

So essentially if the conversion device will drop into a semi-auto host and convert it to a machinegun you should be good to go.

That said the regulatory agency (BATFE) in charge of these matters has taken a historically wishy-washy stance on what guns they will write an opinion letter on regarding what sears can be used in what platforms.

There are a couple of guns out there that can physically accept an HK trigger pack but are not strictly speaking a legacy HK9X platform gun.

Off the top of my head:

1.LUSA – MP5 looking PCC that takes an HK triggerpack but is not rollerlocked.  (Just blowback)
2.SW/Coharie Arms SP10 – Plastic UMP looking gun that takes an HK trigger pack but is roller delayed.
3.HMG Sturmgewehr – STG44 clone that takes a HK triggerpack.

There are also all of the rollerlocked guns that are technically not a direct legacy 91,93,or 94 clone and/or didn’t exist pre-86.   Guns like the semi 23Es, PTR 7.62 guns, MP5/10/40, Dakota 300BLK guns.   However these guns are generally considered on the internet to be mechanically close enough to the original 9X series that sear use is generally accepted.

The other big one most folks like to debate about is the MGA 249.

The original MGA platform required a special “long” hammer so the HK trigger pack was technically unique to that platform. Running one on full auto  meant using a proprietary long hammer with a sear notch on it.   The current gun uses a 100% factory HK pack with a standard hammer and a HK trigger pack  pack will drop right on and run.   Is there a public letter confirming this, not that I am aware of so it’s up to the purchaser to decide if they want to risk it.    Their latest bolt carrier group is also now more clearly advertised for use with legal sears vs. the old verbiage that was a bit more ambiguous and if you talk to MGA, they claim they have confirmation from the ATF it is fine but are also unable to produce anything in writing either.

The only platform that FNC sears are currently legally accepted to work in are the legacy FNC guns even though the SCAR FCG is basically identical to the FNC and SCARs even have a native autosear pivot pin.  There are also a acouple other FN guns that the FNC sear will drop into and convert but there are no approval letters stating its legal to do so.

Which guns?

Unfortunately public discussion on those platforms is somewhat taboo/against the COC here.

My advice would be to take a look at the historical FN semi-auto product line where they have made mechanical changes to the original design and in response the older versions command a significant pricing premium on the open market.

If you get why those specific FN guns command a significant premium and mechanically how they work... it should be pretty obvious which ones I am referencing.

Sorry to be wishy washy here but don't want to get this thread locked or a warning.   (Feel free to PM me if you have specific questions.)

I met  a local guy at my shooting range who got some letter from the ATF or he claims to have one, he's an SOT whatever but he an FNC sear to work on his Scar16.

Wasn't a postie...

super skeptical but he claims to have a letter.

SCAR is very clearly the product improved FNC. The early SCARs used a modified FNC lower with FNC fcg and (iirc) were internally referenced within FN as the “super fnc”. It’s total BS for atf to say the SCAR is not of the fnc family.

The NFA and Hughes amendment is BS in general.

But most specifically yes I don't know how they can say which firearms a sear can and cant be used in. The sear is the registered MG, who gives a damn what I put it in.

Its fine to put it in a semi-auto host that is built from the ground up to work with a sear, but If you take a SCAR and make a few mods to fit a FNC sear that's a no no.

You can use a Shrike on a RR lower or semi auto lower with RDIAS, but put a modified MG34 upper on it and the gates of ATF hell and fury open up.

There was an attempt to put a modified M249 and RPD on a Mac 10 that didn't fly, but if Lage or other manufacturer makes a belt fed upper it will get the thumbs up.

ugh

I saw what the guy did  on his Scar 16, he did exactly the same thing that is needed to be done to an FNC to make a Curtis Higgins Sear work on it.  We sat down at the range in the back room and I saw it with my own eyes, side to side, it looked exactly nearly the same.

What a trip.....

The crazy thing about the SCAR is that the sear pivot pin is already in the SCAR as part of the bolt hold open device.  Technically its called the Bolt Catch Release Support.

If you follow the thread below you can see the sear slot, pin hole, and the little bushing on the semi bolt catch release support where the auto sear would normally go.

https://fnforum.net/forums/fn-scar-16s/23351-guide-complete-lower-receiver-disassembly.html

here without the bushing/spacer:

https://www.midwestgunworks.com/page/mgwi/prod/F145760010

with the spacer installed on the right side/narrow end.

https://lh4.googleusercontent.com/-ov3NahcAl5U/Tpt_OKTkkzI/AAAAAAAABK4/xelTeFoGJ7M/s640/IMAG0452.jpg

On an FNC you have to mill a slot and punch a hole in the receiver to install the sear.  On a SCAR the slot and pin are already there and an FNC sear if not "drop in" is pretty close.

The FNC sear hammer engagement leg is shorter than a factory SCAR sear leg so you would have to weld up the catch ledge a bit different on the SCAR hammer in a more forward position.

The only other thing you need to do is cut another notch in the selector to allow it to rotate to the A position as the semi selector has the disconnector depression engagement point (it just wont rotate to that position) and the disco and trigger are one in the same between the full auto and semi auto.

You would also have to weld the trip back onto the underside of the bolt.

Overall, in my estimation there is actually less work to convert a SCAR using a FNC sear than there is to convert an FNC using an FNC sear.    The only caveat I can think of that precludes using an FNC sear in a SCAR is that you have to make a custom modification to a SCAR semi hammer to allow the FNC sear to engage and hold it back....which could be considered "a post sample machinegun conversion part".  However, the semi FNC hammer requires roughly the same modification as a factory FNC sear engagement leg is longer as well.

What would be really interesting exercise is if somebody made a SCAR lower that used all FNC fire control components.  You could buy one of those SCAR billet lowers as an "80% style" without the fire control group pin holes machined and then figure out the relationship to drill it for a set of FNC fire control parts with an FNC sear and submit that for classification to the tech branch for use with a SCAR as it now truly a "hybrid" gun using all FNC fire control parts.

This is my opinion too, and keep in mind there is no Case Law I know of that says otherwise. Also, when you made an sear, you  were not required to state what weapon it was designed to convert. As I have mentioned on this forum before, I did F1 before 86 for a sear, and only I know what it was for HK, AR, FN, Glock, guess all you want.

Very interesting thread indeed...
Regret selling my FNC sear

Scar 16 - bah.  I wanna be able to use a FNC sear on a M249s!  Now I'd buy that for a dollar!

How about a 249 "upper" on a Mac style RR?

Scott

Uh, that’s been done before by Ernie Wrenn. ATF said no dice.

As I recall they deemed the upper a post sample machine gun.

They did. Both the m249 upper and the RPD upper.

To me the real question is, why was the belt fed "upper" that Ernie made determined to be a Post Sample machinegun?  It is my understanding that the "upper" was made from a rewelded Post Sample receiver. I also think that since the SIG sued as to the determination of the pistol brace, the FATD has to base their determinations on the law. I think that moving forward, new submissions will be evaluated with more basis of the design than the whims of the leadership.

Scott

The whole story can be found by searching online. Ernie was fighting ATF, but then got hemmed up in legal trouble with ATF and the fight over the beltfed uppers withered on the vine. There are court documents that are public record.

That is true. But I also think that the circumstances for such an upper are different today.  Welding a Post Sample receiver back together then modifying it seems problematic at best. Starting with material that was not ever a firearm and being mindful of the placement of the recoil spring would be at the top of my list. If an adapter can be made that allows use of standard AR-15/M16 uppers on a Mac style RR that gives M16 RR functionality, I would think most any firearm mechanism could be adapted to the Mac style RR family. YMMV.

Scott

I completely agree.

Kind of related to this topic- what are transferable HK sears going for these days?

Low to mid 30,000 range.

Scott

Shoot...  how about DLO or LaFrance packs?

About the same with maybe a slight premium, say maybe mid 30s.    I personally think quality sears (Fleming, Qualified, S&H) are a better option over the registered packs that are out there.

All of the registered packs out there are native SEF config so if you want to run them in a modern ambi setup it requires a permanent modification to the trigger box to enlarge the selector axle hole and punch the selector spring pin hole as well.   (with the exception of those "time machine" registered ambi/burst packs that didnt exist pre-86)

The LaFrance packs are/were also native semi-auto trigger boxes with effectively an unregistered conversion style sear in them and its pretty gray area to me to weld up a semi-auto pack to full auto configuration and then "dispose" of the semi-conversion sear.   I would personally never touch a reworked LaFrance pack that had been turned into an ambi/burst that discarded the original conversion sear.  Maybe if the conversion kept the original conversion sear and set it up like a traditional sear based ambi/burst pack but at that point, its just a sear married to a registered triggerbox.

The DLO packs while factory full auto trigger box have their own challenges as well.

The ones that seem to be the best option are the Neal Smith packs as they were original semi-packs converted to full auto spec pre-86. Granted again its pretty much a one way road to ambi/burst land once you mill out the selector hole.

They will work in the Scar and the ATF has said no.

The RPD on the Mac did originally fly and had 2 approval letters. The RPD was revoked when the inventor embarrassed the ATF in federal court on a gun case. A great example of government abuse

just like Brian Poling's BRP upper in 8mm MG34