SWD Lightning Link

03/26/04

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SWD Auto Conector

The SWD Lightning Link (SWD Auto Disconnector or Auto Connector) is one of those unique solutions where someone happened to look at the operation of the AR-15 and how the various parts of the operating systems work together to find an easy way to convert a semi-automatic firearm into a fully automatic weapon. Please understand that it is illegal for a US Citizen to build one of these units without special licenses and the purpose of this page is to discuss how the Lightning Link works and not to provide guidance on how to build one. 

In normal semi-auto operation the hammer is cocked by a rearward movement of the bolt carrier, as the carrier moves forward, the hammer is caught and held in the cocked position by the sear located on the forward part of the trigger catching in the sear notch, on the hammer. If you hold the trigger after a shot's fired the sear will not catch in the hammer's sear notch when the hammer cocks because the sear is depressed below the arc of the hammer notch.

This happens because the trigger is being held back by the hook on the disconnector which is tipped forward and in position to catch the hammer, stopping it from following the bolt carrier forward. When the trigger is released, it allows the hammer to slip from under the disconnector hook and to be caught by the trigger sear in the hammer sear notch. Making it necessary to pull the trigger for each shot. As long as the trigger is held back, the sear is held below the arc of the hammer notch. The only thing holding the hammer in the cocked position is the disconnector. The Lightning Link accomplishes full-auto fire by pulling the disconnector to the rear forcing it to release the hammer.

Operation of Lightning Link


The lightning link is installed by removing the rear take down pin and pivoting the upper by the front pivot pin. The lightning link is then dropped inside the lower with the paddle pointing up, making sure the LL loop goes in front of the disconnector hook as shown in the image above. I have read that the gun might be tricky to close as the paddle has to fit inside the gap between the upper and the bolt carrier. One trick that might help is to point the muzzle of the rifle down as you close the upper receiver. I also understand that sometimes it may be necessary to shave some steel from the carrier to make room for the link. Care must be taken not to remove too much material as obviously this would affect the operation of the link.

Instructions for the Installation, Operation, and Removal of the
S.W.D. AR-15 AUTOMATIC-CONNECTOR


Click for a larger image!

In operation the take-down pin post acts as a fulcrum point. When the bolt carrier strikes the top of the links paddle and the lower end is rocked to the rear, moving the body of the link backward about 1/16 inch, releasing the hammer from under the disconnector hook.

Side View of Lightning Link

As long as the trigger is held back the rearward movement of the bolt carrier will cock the hammer under the disconnector hook. The forward movement of the carrier will strike the upright paddle of the link just as the bolt locks in battery, releasing the hammer, and firing the weapon. When the trigger is released, the sear will stop the hammer in the cocked position negating the operation of the disconnector and the Lightning Link.

223 Bolt Carrier Groups and the SWD Auto Connector


AR-15, SP-1, and M-16 Carrier
Click for larger image!

bulletTop: Normal AR-15 Carrier
bulletMiddle: Colt "SP1" style Carrier
bulletBottom: M-16 Carrier

The rounded AR-15 Carrier (top) has more material at the rear of the carrier as can be seen in the photo above when you compare it to the Colt SP-1 style carrier in the middle.. When you try to use one of the top carriers with a Lightning Link, the link will hit the rounded edge at the rear of the carrier before the carrier closes into battery allowing the rifle to fire.  NOTE:  This is a very dangerous situation and anybody with a link needs to read the timing section that follows to prevent a KABOOM!

The SP-1 carrier, the one in the middle, with it's square back is the carrier that the lightning link was designed for.  This style carrier allows the bolt to nearly close before the link is hit tripping the disconnect.  A person would still want to check their timing before using live ammo but this is the carrier that will work with the link.  

The bottom carrier in the photo above,  the M-16 carrier will not work with the link but I have included it on this scan so you can see how the SP-1 carrier was made by cutting down an M-16 carrier. It would be possible to make a SP-1 type carrier from a M-16 carrier or simply mill an AR-15 carrier to the proper profile.  Also, following is a photo of the newest style Colt "Open" Carrier that was designed specifically to prevent the use of the Lightning Link.  As you can see, the Colt "Open" carrier has no trip surface that will work with the link.

Open style Colt AR-15 Carrier
 

9mm Bolt Groups and the SWD Auto Connector

Full Auto 9mm Bolt and Bolt modified to work with Lightning Link.
Click for larger image!

bulletTop: Normal RRA M-16 Compatible 9mm Bolt
bulletBottom: RRA 9mm Bolt modified to work with Lightning Link

From the discussion of the 223 bolts above, it should be fairly clear what is needed to make other bolts work with the SWD Auto Connector.  In the photos above I am showing my RRA 9mm bolts.  The top bolt is a new RRA 9mm bolt that will work with an AR-15 or M-16.  The rounded area in the slot in the bottom of the bolt is designed for a GI Auto Sear to function and the trip surface is in the proper location for the M-16 or DIAS. 

To make a 9mm bolt compatible with the lightning link, one needs to mill the carrier as shown at the bottom of the photo above.  In essence, all that is done is to mill the carrier to emulate the rear surface of the SP1 carrier as shown in the photo above of the 223 carriers.  When performing this work, it is essential to test the timing of the Lightning Link and the directions that follow will give you an idea of how to confirm your timing is acceptable.

Following are two photos that show the 9mm bolt that was modified for the Lightning Link inserted into a upper receiver.  The top photo shows the 9mm bolt pulled to the rear while the bottom photo shows the gap between the 9mm bolt and the rear takedown lug that is normal with a carrier designed to be used with the link.




Lightning Link modified 9mm Bolt in AR-15 upper
 

Registered Lightning Link Timing made easy

Provided by Dano523 of AR15.com
 

With the link in the rifle, hold the trigger back and cock the action, then slowly ride the cocking handle all the way forward/closed. The hammer should not release. Then while still holding the trigger back, pull the cocking handle back 1/2", then release and let the carrier slam forward. The hammer should be released.

The link cams the disconnector free from the hammer, but due to the slight slop in the design, the carrier must slightly free run for the link to work correctly. If you are able to get the link to release while slowly riding the cocking handle down, then the release timing will be too advanced, and the rifle cycle rate will tend to be a bit too fast.

In regards to adjusting timing, you can always just change the paddle/thickness, but to fine tune, removing a bit of metal from the carrier ledge or disconnector contact point is a simpler way, especially if you are installing a modified burst FCG, and want the link to work with it.

The quick way to time for the modified burst kit is to use a thicker paddle and enlarge the notch in the disconnector (right side burst disconnector) to re-time the link to the FCG kit. The center disconnector should never contact the link; it is controlled/camed out of play when the selector is set to auto, and keeps the hammer retained when the selector is set to semi.

Note: Never file the link; it's the high priced item. Always adjust the parts that can be replaced at will from the box of spare parts.

The Selective Fire Lightning Link

One complaint I've ever heard about the Lightning Link is that the link converts the firearm to full auto only. This issue was solved by a clever idea that Scott Bell came up with while he was working with John Norrell in about 1990.  The solution, which was worked out in a few hours one afternoon, was to use modified parts from an M16A2 fire control kit to control the mode of operation of the Lightning Link.

Lightning Link Selective Fire Kit

Lightning Link Selective Fire Kit

The M-16A2 trigger group has a pair of disconnects that allow the the selector to use one or the other disconnector during firing.  The selective fire kit as Scott Bell and John Norrell developed it, uses one disconnector that has a notch cut into it preventing the LL from tripping it, while the second disconnect does not have this notch and is tripped by the link causing full auto operation as with the standard AR-15 disconnector.

Lightning Link with Selective Fire Kit installed in AR-15

Lightning Link with Selective Fire Kit installed in AR-15

Selective Fire Kit with link removed

Special thanks to "Chris" for the photo above!

Special thanks to "Chris" for the photos above!

A potentially NEW way to get selective fire with a Lightning Link!

I have been working with someone else that has come up with another system that provides an selective fire option for the Lightning Link, but this kit uses Modified AR-15 parts.  The advantage of this new system is that the Lightning Link could be removed from the lower, or more accurately in the eye of the law, the AR-15 can be removed from the Machine Gun (Lightning Link) and there would not be additional M-16 parts remaining in the AR-15!

Details of this new kit can be seen ON THIS PAGE!

AR-15 Lowers that will work with a Lightning Link

The following is information from Circuits, a member on AR15.com who is a Class 07 Firearms manufacturer and a Class 02 SOT NFA weapons manufacturer.

To use an SWD Auto Disconnector with an AR-15s it is essential that there is at least an 1/8" clearance under the takedown pin post for a lightning link to work. All Bushmaster, Sendra, Essential Arms, and some PWA preban lower receiver will work perfect without modification. Some early Colts such as pre-89 SP1 and Sporter II will also work perfect without modification. Later Colts (post-90 to mid 90's) will also work perfect if the pinned-in sear block is removed.

Most Olympic Arms lower receivers may need internal filing to fit a DIAS or a lightning link. This is because they are not built to the same specifications as the early Colt or bushmaster, and are too narrow by a few 100ths of an inch to fit a DIAS or link. Preban Eagle Arms lowers will fit a DIAS but not a link in Circuit's experience because it is slightly too large internally to support the link and let it work.

Other lowers such as late-90's post ban Colts have unmachined web sear block and high shelf while Postban Eagle Arms, Armalite, ASA, and some PWA prebans and all PWA postbans have a high shelf that will need to be milled out to allow a lightning link to work.

Advantages of the Lightning Link

1. Relatively inexpensive way to get a full auto M-16
2. Selective fire capability.
3. Can be removed from weapon and stored in a small secure place.

Disadvantages of the Lightning Link

1. Physically can wear out over time.

2. Getting a link to work with a Ciener 22 conversion can prove a difficult challange.

 

 

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This site was last updated 03/23/04