Full Auto for Any AR: How a Lightning Link Works

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Commonly known as the “Lightning Link” the S.W.D., Inc. Auto Connector is a rarity to see these days. With fewer than 900 manufactured and registered in the NFA registry, the Lightning Links are a novel way to convert a semi-automatic AR-15 into a fully-automatic firearm. While the conversion is two-way (meaning can be installed and removed without issue), the Lightning Link will turn the firearm into full-auto only as installed.

Its physical operation is interesting for those looking at weapons design. Rather than require modified hammers and other full-auto parts, the Lightning Link was designed for off-the-shelf commercial AR-15 rifles without the sear block. It normally consist of two parts, the main link and the sear.

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The kit requires the use of a true AR-15 semi-auto bolt carrier group. Installed, it hooks around the disconnector and the rear portion fits behind the lug of the upper receiver using the lug as a lever point. As the bolt carrier returns to battery, the rear portion of the bolt carrier group catches the vertical portion of the link, causing it to pitch forward pulling the link to the rear which in turns pulls the disconnector to the rear releasing the hammer for the follow-on ignition.

YouTube user “Magoo6541” has a great (if older) video showing a real link installed and a few videos with one working in a firearm for those wanting a video explanation:



Nathan S.

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

Nathan can be reached at Nathan.S@TheFirearmBlog.com

The above post is my opinion and does not reflect the views of any company or organization.


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  • Lightning links require a specific bolt carrier actually, not just any semi auto one. They must have the old Colt SP1 square cut on the bottom of the tail and timing them can be a pain.

    • PK

      100% agreed on the timing! Modifying the carrier isn’t a big deal, luckily. I’ve helped lots of people modify everything from 9x19mm carriers to 22lr carriers to the newer ultralight carriers. A very light carrier ended up reliably getting over 1,200RPM with a RLL, which was just too much fun.

      • Drew Coleman

        What caliber for the 1200 RPM one?

        • PK

          5.56x45mm. We ended up modifying a JP LMOS BCG, basically just milling the rear back to trip the LL. Even running with an adjustable gas block, it was showing quite a bit of wear after a thousand rounds, but that was to be expected. If I’m remembering right, it was right around 135 grams fully assembled.

          Next up is building a 7.62x25mm belt-fed upper based on the Freedom Ordnance 9x19mm design, just stretched a bit and DI instead of blowback. With DI, we can trim off a whole lot of reciprocating mass and get it running fast.

          • randomswede

            So heavy recoil spring, “lots” of gas and minimal BCG and buffer weight?

          • PK

            No, not at all. Turned the gas down until it just cycles, standard 3oz buffer, standard spring, and a light BCG. The lack of a (relatively) heavy reciprocating mass is the real magic, objects at rest tend to stay at rest, etc. The lighter the reciprocating mass in a firearm is, everything else being the same, the faster it cycles.

          • randomswede

            That makes sense, I would have thought getting it over the 1000 rpm mark would be hard with “just” a lighter BCG so thank you for sharing.

            It does make me wonder at what RPM an AR-15 won’t make it through a 30 round magazine without self destruction.

          • PK

            Multiple people have bumpstock AR15s running 1,400-1,600 RPM, reliably. I’m not sure what you’re asking about damage occurring, do you mean from overheating? If that’s the case, the answer is the usual “it depends”. If you’re running it while overgassed, the first thing to go is generally the interface between the gas key and the carrier itself, which has (more than once) blown the side off the upper. It’s dangerous to run ARs overgassed, even more so when the carrier isn’t good steel!

          • randomswede

            1600 RPM is already low end multibarrel territory and astounding, but at some point any system will start tripping over itself.

            Something along the lines of the BCG coming back so violent that the top round in the magazine is pushed down so hard it can’t make it back up to the top before the bolts has passed the rim.
            Just as an illustration the absurdity of problem I was getting at.

          • PK

            Oh, you’re talking about bolt over-run or outrunning the magazine. Yeah, I haven’t gotten there yet with the 30rd STANAG mags. We’ll see.

          • Lonnie

            I find it hard to believe 1,400 RPM with a sliding stock. Firstly, you would never be able to actually achieve that round count with a magazine fed firearm. At 1500 RPM you are dumping 25 rounds per second. If you are the fastest mag swapper to ever live and can do it in one second the most rounds you can get off would be 750 RPM. I personally would not want to be anywhere near an AR firing that fast because something will give, sooner or later.

          • PK

            Approximately seven hours ago I tried to link a YouTube video for you, but it’s still pending due to offsite linking.

            If you’d like to view the video yourself, the title is “BumpSAW Surefire 60 dump 1400RPM” uploaded by “jaqufrost” and the YouTube video ID is “A3SVErXz6dY”.

            I think a large part of your surprise is effective RPM vs cyclic RPM. I meant cyclic, surely, as even belt-fed weapons with a single barrel aren’t suitable for much sustained firing, bursts only. You’re entirely correct on that point, of course!

            Enjoy the video.

          • Machinegunnertim

            Serious? where are ya going to get the 7.62×25 barrels? I’m asking because I am working on 2 AR’s in that caliber as well.

          • PK

            Yes, I’m quite serious. I’ve already made the barrel, 7.62x25mm is the same bore diameter as US .30 cals, so blanks are all over the place. Just be mindful of the twist rate and headspace when you chamber it, that’s all.

          • Machinegunnertim

            Email me. My screen name, at gmail dot com.

          • PK

            Sent you an e-mail a short while ago, hopefully I can point you in the right direction.

          • Anonymoose

            I would put that 1200RPM one on a pintle mount with a C-Mag and use it for suppressing squirrels and possums.

      • josh

        holy hell… that must have been awesome!

      • Ondřej Turek

        Luckily? This DAMN thing quite helped in arguments to ban the AR-15, every single variant, in every member state of the EU. We’re fighting in the last line of defense against an EU-wide ban and the Swedish gun-grabbers got their hands on the Lightning Link argument.

        In a world where “ease of convertibility to fully automatic” is massive argument for politicians trying to add some rifle to a ban-list, any attempt to make rifles easily convertible to full-auto equals sabotage against fellow shooters.

        • PK

          I’m sorry you’re frustrated in your attempts to legitimately own modern firearms in your country, but please don’t blame me for that.

    • Christian Hedegaard-Schou

      From what I understand they will work with colt-pattern 9mm bolt carriers out of the box because they are cut in the rear at the same location the SP1 carriers are.

      Would love to get some confirmation on that one though.

      • HH

        Well I have a FM-9 Beltfed 9mm upper mated to an Anderson AR15 lower running FA w a RLL. Absolutely rocks.

    • Anon. E Maus

      Correct me if I’m wrong, but a Lightning-Link won’t actually fit in a regular modern AR-15 receiver, right?

      • HH

        “Modern” receiver like say an Anderson lower? No, it won’t drop in. In fact my RLLs don’t truly drop into any modern receivers I’ve come across although I’m sure they exist. Must be SP1 configuration as Alex said. That includes being a “Low Shelf” lower. Colt in their wisdom back in the day voluntarily decided to raise their “shelf” ( maybe to appease the govt to maintain contracts, etc even though ATF doesn’t -didn’t require high shelf) which then precluded drop in of RLL. While numerous low shelf lowers are sold today ( including some Andersons) even they can’t accommodate drop in RLL. I’ve found that they still don’t ” square out” the back of the shelf sufficiently. Nor do they allow adequate room for RLL “protectors”. Pretty much everyone with a RLL runs them with a KNS protector. This removes stress from the link itself preserving its working life essentially making it a non wearable part which is cool.

        Bottom line: most all lowers today require a minor bit of LEGAL milling ( no additional sear hole drilled, etc). Easy to do with simple dremel more or less. Also oftentimes the rear lug require a few thou milling to allow for positive upper-lower mating.

        RLLs are not compatible with M16 fire control parts or non-SP1 config. carriers. The latter simply need their back slot milled to SP1 config. to be compatible.

        With RDIASs running north of $30,000 today RLLs at 1/2 that price are excellent relative value in the NFA world. And remember even RDIASs require timing/shimming.

    • Denis Allen

      SP1 carriers at Youngs Manufacturing and are an exact copy.

  • PK

    Timing these is so very important… but they sure are entertaining and used to be quite cheap. These days, RLLs seem on par with RDIASs and even some converted RRs.

  • gunsandrockets

    Huh. Thanks for that.

  • BryanS

    Only metal more expensive than that (and isn’t made in a lab) is an H&K pre 86 sear, at least by weight.

  • Ken

    While they are full auto only using a standard semi auto AR, you can make them select fire using the trigger and double disconnector from a burst trigger group. You cut the hook further back on the left disconnector with the tail, so the lightning link doesn’t engage it.

    • PK

      I seem to recall reading about doing just that on Quarterbore’s website, years ago. Seems like a very clever way to achieve both semi- and full-auto functioning with just the RLL, although owners in some states (CT springs to mind) can’t have select fire weaponry, only semi- OR full-auto! Go figure.

  • Widgt

    16K…staggering.

  • gone or rea

    In NY we’re not allowed the semi auto version with a 10 rd mag. Black Guns Do Not Matter

    • jerry young

      move to a state that allows you to own real guns

    • The Brigadier

      Sonny Cuomo strikes again. Why don’t all of you in NY file a group suit against your Governor? It will take a few years, but by that time O will be out of office and with any luck the Beest will be defeated. You really shouldn’t let your left wing fanatics run over you all like that. Taking back America does require some backbone.

      • gone or rea

        Because at every level here it is the corrupt Dem machine, from local reps to the judges, even the NY republicans are as much anti gun as the Dems. We have maybe one or two reps for us, the rest are bolsheviks, even the NRA has given up on NY.

      • Old Vet

        You hope the Beest will be defeated. If Comey doesn’t step in we will be the victims of a (Clinton) stolen election, no matter who you voted for, in my humble opinion.

  • PK

    And that’s my main problem with the RLL market these days. This year, 2016, I saw RRs for sale (yes, converted and not factory) for a similar amount, although through classified ads instead of auction… which, now that I think about it, may account for the price discrepancy.

  • Jas

    Interesting but worrysome detail: Presently in Europe they are talking about banning semiautomatic firearms because these are extremely dangerous and should not be in private hands. One of the reasons they give is that semiautos can easily (in a few seconds) be converted to fullauto. The two examples they (we are talking about the European Commission) keep repeating over and over again: The Glock with the switch on the back of the slide and the AR 15 with exactly this lightning link. Complete with the youtube film shown in this item. Give’m something they do not understand and they will use it against you.

    • Pod

      They say “easily” but realize the people who can do this are competent with firearms and machinist skills. I could give some thug an AR and a Lightning Link and he’d be clueless since there isn’t an app for that, or it’s not featured on Worldstar.

      As for the terrorists over in the EU, they aren’t converting semi-auto weapons, they’re getting the real deal from Africa and Eastern Europe.

    • I’m sure any such EU legislation will be faithfully followed to the letter by anyone planning a mass murder, and that the next right wing Norwegian extremist bent on massacre absolutely will not just motor on over to one of the Former Soviets and buy a crate full of cosmolined AKMs from the back of a van on the side of the highway.

      The obliviousness of politicians is one the universal truths around which all the many and varied peoples of the world can unite in common frustration.

  • Pitt

    With 3 shot burst trigger group does that lower have to also be registered wifi LL?
    Thought LLs were serial numbered themselves.

  • Mike Lashewitz

    I might sound stupid here but why are they talking about full auto but show a semi auto BCG in the image?

    • DChrls

      Read the article

      • Craig

        Exactly. The Daniels (Sylvia and Wayne Daniel = SWD) abhorred the NFA and tried every single thing they could to get around it for Cobray customers.

        The “readily convertible to full auto” clause was repeatedly tested by them, when they once even offered a mac 10 as a ‘single shot pistol’ by merely welding up the mag insert on the gun.

        The lightning link was another method of theirs that was frankly ingenious. They looked at the majority of AR15s and found a way to make them autos. They really were sort of a Bonnie and Clyde firearms pioneer couple, known primarily for their Macs (which they actually only designed the m11) but the lightning links, street sweepers and conversion receivers are all really interesting pieces. My polytech is an SWD conversion.

        All in all, theirs is a really neat story. Great for a Sunday morning read. I’m not certain, but I was told once that their son is the guy who created Tapco as well.

  • Larry

    All the talk about full autos. I dare say that maybe 1:1000 have any idea how to shot one. Expend all of your ammo, and all you do is put holes in the sky. Unless you live in the boonies without having anyone within five miles, there is no place to even shot it. If you do fire a full auto group, plan on the Feds to be at your door step. The best thing to do is get yourself a good single stage trigger (not a mil-spec type), learn to shot it properly and all 30 rounds will be on target at a high rate of speed and accuracy

  • gone or rea

    In NY state we are held hostage to unconstitutional gun laws, everything at every level is part of the corrupt democratic 4th Reich, and the irony is that they are mostly Jewish instituting Nazi-like laws that disarm the law abiding citizenry. The SturmAbtielung such as Charles Schumer, Eric Schneiderman and the other NYC Yentas, with Der Fuherer himself, Andrew Cuomo, a guinzaloon from Tramonti, Italy.

  • CountryBoy

    How can this be Legal ???? You are altering the operation of the firing group, the part of the gun that is actually REGISTERED with a serial number….. If you would do something like modifying the sear to go fully auto, you would be committing a Felony. How is this any different ???

    Any malfunctioning semi-auto that multi-fires is an illegal gun that can be confiscated by the authorities… and you can be charged.

  • Bob

    the article says 900 manufactured and registered in the NFA registry.
    So, I would presume they paid the $200 tax stamp and have their form 4 to carry with the firearm.
    I would NOT be messing with a FULL AUTO without the proper paperwork and taxes, etc.
    Camp FED would not be much fun!

    • Mike Lashewitz

      Shall not be infringed?

      • Bob

        I agree with you Mike, but the gov’t does NOT HONOR our constitution and has been practicing “selective law enforcement” (Lawlessness) for quite some time now.

  • I Would just stick to my crank fire setup. It’s cheaper, and it’s legal. The only downside is the amount of ammo that expended.

    • nicholsda

      As are SlideFire stocks. And they too can eat a ton of ammo.

  • Mike Lashewitz

    Yes this is really cool. But I prefer not wasting ammo.

  • gone or rea

    I dont give a rats ass, was to point out insanity, not Judaism.