I am curious if anybody has any feedback, opinions, or experience with the method of achieving select fire capability while using a lightning link (RLL) by engraving a notch into a semi-auto disconnector and modifying the selector to allow the RLL to engage/disengage the notch. I am specifically referring to the method described here:  Quarterbore's RLL Select Fire Page



I have started to modify the parts, but from what I see there is no way for the RLL to rotate up out of the notch with the BCG in battery. Whenever the RLL is in the lower and the BCG is in battery, the RLL is pulling on the disconnector and is in tension. This means that the RLL is pulled into the notched out area. If one were to try to rotate the selector switch, the link would just hit the top of the notched out area and not allow the selector to rotate. Has anybody ever gotten this to work, I never heard of any reports online.  Or, is there a fundamental limitation with this method that one would need to pull the charging handle back or have the BHO engaged in order to rotate the selector from semi to auto?

Note that this method has completely different from the modified burst kit method of achieving select fire for an RLL.  That method works great...no issues there.

Thanks in advance,
Esox

I don't  think it's ever even been tried, since the modified burst is known and works so well.

The idea is that normally with the selector in semi the link body lies flat on a machined area on the selector and leaves the disconnector untouched because of the slot. Then when the selector is rotated to full it cams the link body up so that it will act on the disconnector.

In practice I doubt the link can tilt enough, between the takedown pin post, the disconnector and the body of the hammer,  to make it work.

I will preface by stating I have never performed this modification.

However, I think the part you may be overlooking is that when the bolt carrier is in battery and the link body is pulled to its most rearward position, the link does not pull back on the disconnector (at least in my experience).  With the trigger in its normal resting state the disconnector is back away from the hammer. (i.e. it isn't engaging the spur on the hammer).

When you pull the trigger obviously the front of the trigger drops releasing the nose of the trigger from the notch on the hammer and the hammer falls.  However, the trigger pull also rotates the disconnector forward to engage the spur on the hammer.  The lighting link only can really engage and pull back on the disconnector when the trigger is pulled forward and the disconnector is in the position to catch the hammer spur.   Under normal operation, the RLL can then pull back on the disconnector  to basically its normal non-trigger pull  position, which releases the hammer.

So when the trigger is not pulled the link is essentially free to be moved up and down against the front face of the disconnector, even if the carrier is in battery.

One of the somewhat unanticipated benefits of having a Shrike set up with a RLL is that when you open the top cover you can see everything interface together, almost like a cutaway firearm.

Anyway.....my suspicion is that for most folks the reason this setup wont work isn't that the link isn't free to move up and down the face of the disco (engaging or disengaging the slot) its that if you run a RLL protector the clearance between the bottom of the rear lug and the shelf is almost non-existent, so you wont be able to cam the link up or down with the selector since it is basically just short of being pinched between the rear lug and the receiver shelf.

If I had to choose between no protector and this setup vs. a protector and a modded burst setup, I will go protector + modded burst.

I guess if you wanted to try and thin the rear lug down a bunch,  lower the shelf even further, and grind down the selector to make clearance, you might get it to work.   However, as others have mentioned why bother since the modded burst works so well.

I guess I'll be the guinea pig here then.  The reason I am interested in trying this, aside from testing out my WECSOG skills and pure curiosity, is that if it works then it offers the ability to have a variety of RLL hosts with no M-16 parts in them whatsoever and each would have drop-in select fire capability rather than just safe/auto capability. Apparently some people are interested in this for fear that the BATFE frowns on any M-16 parts in Title 1 guns (even though most carriers are M-16 nowadays anyhow and the modified burst parts would never allow auto function alone).

I've already cut a notch in a semi-auto disconnector. My next step will be to donate an M-16 selector (so I don't need to cut a detent groove/hole for the auto position in a semi-selector) and grind off the bottom area to allow it to rotate into the auto position with a semi-trigger and grind the top off flush with the shelf of the lower receiver. Of course if it does work, this would need to actually be done to a semi-selector to eliminate any M-16 parts.

I have not and never will shoot my RLL without the protector installed. So this would need to work with it or it is a showstopper. I already have the rear lug on one of my uppers ground down so much that there is only about a 1/16 of an inch of material left on the bottom. I think I will also grind down the bottom of one of my paddles to allow more clearance for the RLL to pivot as well.

I just don't see how when the BCG is in battery and the trigger is not engaged that there still isn't a little bit of pressure that the RLL has against the disconnector. It doesn't seem like the disconnector would rock that much forward with the trigger pulled. I seems like whenever I put my RLL in and I close the upper, I feel a little pressure like the link is pulling against the disconnector. If this works, it should allow for easier installation of the RLL, right?  I don't know about everybody else, but I keep a toothpick handy to push the paddle up against the lug as I close it shut.

Well, I got it to kinda work. The selector will actually rotate about 30 degrees towards the third position, but that's it. I didn't torque the selector too hard for fear of damaging the link. It will rotate all the way with the bolt held open. I may explore adding a slight radius to the top corner of the disconnector cutout to allow it to slide up into position better. While in the auto position, the RLL seems to be functioning fine with dry fire cycling.

Other than the M16  selector...

I'm just using one for now out of convenience since I don't want to fuss with making a detent channel/stop. If it works then a person could make one out of a semi-auto selector. I don't think the BATFE has any issues with a selector moving to the third position if it is not functional in an M-16 (e.g., the TAC-CON trigger system).

I've tinkered with modifying two disconnectors now using different types of cuts and radii and still cannot get full rotation to the auto position without releasing pressure on the paddle by pulling back on the CH slightly. I am starting to think this method was just an idea and nobody ever actually performed it (successfully at least).

I will continue to tinker and see if I can get it to switch between semi and auto without any other assistance. I have a feeling that if I do find the sweet spot cut geometry it will still be a finicky setup.

Has anybody ever heard of someone getting this to work????

If your link is putting pressure on the face of the disconnector with the bolt closed and which is precluding the link from being actuated up and down due to getting caught in the slot you have milled,  have you considered milling the entire face of the disconnector back so that the link doesnt touch the disconnector with the trigger/disconnector in the resting position with the bolt closed?

You would need to set it up with the tolerance being such that when the link is at it most rearward spot in the lower receiver pocket (i.e. it cant be pulled back any further because the rear of the link "ears" hit the rear of the receiver) at that point the link is say a hundredth off the face of the disconnector with the trigger in the resting position.  It would then be free to move up and down as the link doesn't physically touch the disconnector in its most rearward position.

With the trigger pulled the disco rotates forward to be able to catch the spur on the hammer and the link is now free to impact the face of the disco when rotated up to the auto mode to clear the slot.

Worst case at least you link is free to move up and down at that point but you wont get enough impact to release the disco from the hammer.

This is exactly what I started to do on the second disco that I am playing with. I can't just move the link back to the ears touching the receiver pocket for a reference because I have milled out probably more pocket clearance space than is needed. So far I have not milled enough disco face off for the link to rotate up freely. I am going to keep slowly removing more material until it will raise up, but like you mentioned...I fear that there won't be enough disco travel in the end to release the hammer.

I did donate a cheapo stripped upper receiver to help with the modifications. I cut viewing ports in the left side to visually watch the FCG and the top of the link interacting with the BCG. It is a pretty cool cutaway and does a great job of showing how the RLL works. I may even cut out a potion of the side of a cheap donor lower to offer a better view of the FCG action. If people are interested I may post a video.

That would absolutely be an interesting video!  Please post it, or at least several still photos.

There should be enough dimensional tolerance available.

Think about it this way, with the trigger at "rest" there is enough clearance for the hammer spur to clear the disconnector. The hammer shouldn't hit the diconnector on its rearward travel if the trigger is at rest.   i.e. cock the hammer back with your thumb, the hammer shouldn't hit and rock the disconnector out of the way on the way back to being caught by the front of the trigger. If the hammer hit and moved the disconnector on the way back than the gun would never fire as you would pull the trigger, the hammer would release from the front of the trigger only to be immediately caught by the disconnector.

So with the trigger at rest and the disco at rest the hammer is free to fall with the exception of the front of the trigger holding it back.  Your current setup the RLL is already putting rearward pressure on the disconnector pulling it backward and away from the hammer spur even farther than it would be normally.  By removing material from the front face of the disconnector you are just allowing the diconnector to move forward to where it would be without the link in place and the bolt carrier closed.

With the trigger pulled and the disco now cammed forward, your link would now pull the disconnector back to its previous non-trigger pulled resting position, which we know doesnt allow the disconnector to catch the hammer spur, so the hammer will drop.

I believe I understand now why your link is pulling on your disconnector at rest because you have the rear of the pocket milled back farther than SP1 spec. With a thick paddle and a deeper pocket it allows the link to be cammed back even farther than it normally would.  On my guns the link when pushed back all the way in the receiver pocket it just barely doesn't touch the disconnector, so there is no tension on my link when the gun is just sitting still.

Let us know how it works out.

^^^This is a very important fact that I have not been aware of to date...and it gives me hope that it will eventually work.

My first lower was clearance milled out by a very reputable machinegun smith. My other was milled out by me and my dremel for considerably less money (free). Both have plenty of room to play and have worked flawlessly . This is probably a great thing for general RLL setups, but NOT for this particular project/setup. I will start with a fresh lower and clearance mill back to the point of just barely not touching.

Due to work and family commitments I may not get to this for a few weeks, so please be patient.

Thank you JBNTEX for the key pointer!!

Tried this years ago.

Used a modified Semi safety with part of it beveled to allow the link to drop in the slot for semi.

Worked fine but was not reliable.  Lost interest in the project.  Moved to Lage fun w Max 11's, 22's & 31.

Went back to the modified 16 parts for the link.

Talked extensively w Quarterbore on the project and he decided the same thing - could not make it reliable.  Would be nice if it did wok because only AR15 parts in rifle.

YMMV, FH

FH, if you have the time and inclination, can you please elaborate on any of the details of why the setup was found to be unreliable by both you and Quarterbore?  I'd like to be aware of these issues for when I get around to tinkering on this project again to see if I can help mitigate them.

TIA,
Esox

Not to derail but did anyone ever get a LL to work with a 22 conversion?

never reliably.

Unlike the sear or DIAS which exerts no pressure on the 22 kit's sear trip after activation, the LL trip is still resisting the force of the disconnector spring exerted by the paddle when in battery.

A full size action spring  can easily overcome the force of the disconnector spring to keep a bolt carrier forward, But the weaker action spring  of the conversion kits can't  do the same to keep the conversion bolt in battery.

A resetting 22  trip for the LL is needed, to prevent the disconnector from pulling it out of battery after tripping, if it's ever going to be made to work.

I did this a few years ago. Nothing I can put my name on to offer. Only did bursts, no mag dumps. Next would be eliminating the spring on the kit and making the unit stroke into the buffer tube.  Waiting to slow down to re visit the project.

Awesome let me know if you ever get it to run.

I finally got some time to put together a "virgin" lower to check out the effect of leaving the rear of the shelf in its original condition (i.e., not cutting deeper towards the buffer detent). I used a cutaway lower that I had to help visualize all the moving pieces. So far with a standard MILSPEC FCG, the RLL still works great and had just barely enough clearance for the link to ride up the disco. I will try the modified disco tomorrow hopefully. I am hopeful this will work now, but reliability will be the key.

One thing that I noticed with using the cutaway lower without the rear pocket cut deeper is that the hammer comes dangerously close to the RLL when cocking. It is even closer with the protector installed because it takes away another 0.050" of available space.  I believe this is probably the main reason for the rear pocket...allowing the link to travel farther back to help protect it from the hammer, rather than required for function. It runs just fine without the pocket clearance.

With a blowback upper that has the possibility of trigger slap (e.g., not properly ramped bolt), this would be something in particular to try to avoid. I found a workaround by notching two parts of the hammer. For this particular select fire modification, the link will further rotate up creating a steeper angle, which causes even more chance for the shank of the hammer to strike the front face of the RLL. My improved RLL protector design that prevents selector wear also raises the link on the disco face slightly, which would also increase the chances of this happening without the hammer notch fix.

Bottom line = if you don't have a rear pocket cutout, you might want to check your hammer cocking clearance to prevent possible striking of the RLL.

Sure would like to see some pics or a video

One of the things you can to get additional clearance is to thin the hammer down a bit.  In my experience it doesn't effect function at all and get a bit more clearance, especially around that "hump" area.  Its a pretty simple mod on bench grinder/belt sander.



The custom protectors I make for my links also protect from  inadvertent hammer strikes directly to the link as well.  I also thin down my selectors so that the link sits flush in the bottom of the pocket vs. teeder-toddering over the selector.  Granted for your experiment you need the link to teeder over the selector and even be pushed up higher to allow select fire operation based on a notch in the semi disconnector.

Forgot to check on this thread - sorry.

Worked on this in 2006 I think...

Worked in a fashion but would only do bursts...never really ran true.

I beveled edges as well and did minor milling in the lower for clearance.

Still would lock up after 3-4-5 rounds.

May pull out old parts and give it another whirl.

Quarterbore and I both thought we were right on the edge of making it work but had same issues.

I run a KNS protector as well and it might work better without it but I am not going to try!

Would love to see your videos - especially if you do a super slo-mo w iphone!

Keep tinkering!  The concept is good.

FH

FH, if you were only getting bursts, then I suspect that you just needed a slightly thicker paddle for it to work more reliably. That's because the actual modification you are doing to the disconnector is to allow semi-auto fire, not full auto.  The only other possible ways for it to only allow bursts is if the link ended up tipping back down during fire and was allowed to slide into the disconnector slot that you cut or if your slot was cut just a bit too high up on the disconnector.

I did finally take some phone video of my RLL in the cutaway lower receiver last night with standard FCG (full auto only), modified burst FCG select fire, and this modified semi-disco FCG select fire modification.  I'll try to find time tonight to edit it and get it posted here.

Esox

Thanks for the info and update.

The full video describing the RLL and the various install options and tips/tricks ended up being 40 minutes long. If there is enough interest, I'll upload it. For now, here is a 4 minute video related to my original post. If I can get a kitchen pass in the next week or two, I'll try to get to the range and post live fire video as well.



Hope this helps and special thanks to JBNTEX and others with the guidance. Please note that a key requirement in this modification is that you cannot have a rear pocket clearance cut (not needed anyhow, not sure why people do it). The full video goes into detail on why this is the case.
v/r,
Esox

That is a nice little video with a simple explanation.  I would like to see the full video.

Thanks for taking the time to make and post it!

I think you are right.

I just lost interest in the project but I meant to try cutting the slot at different heights and thicknesses in a couple of disconnectors to see if I could get the right clearance...felt like it was doing just what you said: would fire semi then every once in a while would run away 3-4-5 rounds in a burst...then settle back down in semi.  Was frustrating.

If I had better range access where I could sit and fiddle for several sessions I believe I could work it out.

Maybe this winter when things slow down...until then hope you find a fix!

Currently playing with about six different 300BLK uppers trying to find the best suppressor host for a SDN6...and reloading a metric $hit ton of 220gr 300s because they just are the funnest things to shoot suppressed!  Crazy quiet.  Trying to find a reliable 6" barrel now!

FH

ETA:  Didn't read full thread before I posted:  MAN THAT IS A COOL LOWER!  I need to do that so I can show the internals working!  I love it and can't wait to see full video!

Have you tried your mods in live fire yet?  Also - when you do - lie on your side both ways and see if the link will fall back into the slot or not.

I think your bevels may be the trick - I did not bevel that much.

Thx!

That lower is the "Reaper" model from Daytona Tactical...a good deal at just $75.00.  I bought it to do a fully skeletonized build (with piston upper) as primarily a conversation piece. However it has also become a very useful tool in tinkering and observing the mechanics of the RLL and fire control groups.


I have not shot the mod yet, but I plan to do so...and use the skeletonized lower even though it will be a bit gassy/dirty. If the gun is in "Auto" mode, I don't think there will be any issues with it shooting at a 90 degree roll to either side since it is functioning just like a normal RLL setup. In "Semi" mode, I can see where the link may be able to slide up and catch the disco, resulting in unintended automatic fire. This could easily be fixed by wrapping a weak spring or band over the link and attaching it to the lower. I personally wouldn't do it since its a non-issue for me.


The slight beveling is helpful, but the key is to not use a lower with a rear pocket clearance cut. Also, please notice that I removed a fair amount of material from the base of the disconnector as well. This allows the link to sit as low as possible on the disco. After I verify performance with live fire. I'll post some pictures of the modded disco next to a virgin disco.

v/r,
Esox

The video with cutaway lower is absolutely amazing!
This is the first time I truly understand the function of LL with actual movement in both semi & full.
If possible could you please post the full video?
I'm dying to watch the video.... please~

Sorry, I've been traveling for work lately so have not had time to post the long video. I'll try to get to it this weekend. The file size is huge, so uploading will take several hours for me. If it gets too cumbersome, I'll just break it into smaller pieces and post them incrementally.
Esox

Was going to ask about the M16 selector I saw in your initial post then saw this - this is exactly what I did with an AR15 selector.  Essentially you have two modded AR15 parts - the disconnector & the selector.  Everything else is stock.

I also milled the rear takedown a little for clearance but did not think about the bottom of the paddle - would like to see how much you took off that as well.

Now I am back interested in this mod!  Thanks for getting me back on this subject!!!  Like I don't have enough projects in process right now!

FH

Can't wait to see the video!

Here you go.  My apologies in advance. Its too long for today's short attention spans, but I am not a videographer and I have a tendency to ramble on. I'm kicking around the idea of putting together a website dedicated to the RLL since there isn't a single go-to source for this niche within a niche community.  Therefore, if there are any additional things to add, errors to correct, or other tips and trick, please let me know.
v/r,
Esox

THAT IS EXCELLENT!!!

Bookmarked!

Now you need a slowmo vid of the link in action with the mod to show it working!

Wow!

Also - did you make the extended protector?  I like that as well and would be interested in one if you make them.

The mods on the hammer are interesting also - especially if you do 9mm with a ramped bolt.

Need to crank this project back up!

Thanks & I will join the forum for sure if you set it up.

FH

If I can ever get some free time to go to the range I'll try to post some live fire video and see if I can capture it in slo-mo.  My Galaxy S5 has a mode that is supposed to quasi-capture slo-mo video, but based on my tests so far it sucks compared to what I have seen from the iPhones. If there is an app out there or a tip to make it work better, I'd like to learn about it.

I doubt that I will have a forum if I put a website together. That would be too much work and this ARFCOM forum is already a great place for that. I'd just like to capture as much information to help people out with the RLL as possible. I may even try to get some RLL specific parts made that don't require an FFL and offer them for sale at very reasonable prices, like select fire kits, paddles, protectors, hammers, etc.

FH, PM me if you are interested in the new protector...I'll try to make up another one and send it to you for testing and review.

Thanks,
Esox

You're a genius, Esox.
I've never seen such in-depth & most knowledgeable video about LL in my entire Youtube watching career.
Keep up the great work and it really helped my understanding about its function and many different areas that I only guessed.
Awesome!!!!!!!!!!!!!!!

I am no genius!  All I did was follow the instructions from Quarterbore's website and ask for advice/experience from other members.

Finally got a chance to get to the range. The disco/selector modification worked great!

Unfortunately, after shooting a bit, the paddle I was using started to bend excessively, causing only burst fire. It was a brand new paddle that I made and I think it had too low of modulus (4130 steel, not spring steel). Note to self, always bring extra paddles to the range...duh.  I will also do some forensic investigation and post back whether the lack of a rear pocket clearance cut helped to contribute to this scenario.

v/r,
Esox

Woo Hoo!!!

Looks like she runs fine!

Get that slo mo close in on the link....that will be awesome!

Digging thru the ole parts pile trying to find the discos...found the 15 selector that I butchered up and see why mine didn't work as well...milled off too much on the select fire side...Link not lifted up enough to clear the slot.

FH

Yeah, I need to find a friend with one of the new iPhones to get good slo-mo video. My Galaxy S5 kind of sucks using "sequence shot" slo-mo mode. I may even try using the cutaway upper to get a shot of the BCG interacting with the paddle as well.

As an aside, I was really pretty impressed with how clean and non-gassy the skeletonized lower was while shooting. I thought that I would end up with crud all over my arms and shirt.

I am happy to report that the anomaly of my paddle bending rather quickly in the test fire range trip was indeed due to the paddle material.  At the time I did not realize that the 4130 shim stock I used was annealed, which makes for a very ductile paddle.  I heat treated and tempered the paddles to Rockwell 38-42 hardness and now they run great.  I just got back from the range shooting the same heat treated 0.032" paddle with this setup and it shows no signs of bending and the setup ran great with multiple mag dumps.  I'll try to post some pictures of the two paddles for comparison when I get some time.

For those who have been waiting for some parts to try, now that I am confident in the setup I will start making them up.

That's a great news.
Thanks for the update!!!

Put me on the list to buy stuff!   Sent you an email or a PM a day or so ago.

As requested in another thread, below is an instructional video on how to perform the modifications to a set of M16A2 burst disconnectors to enable select fire with a RLL.

Would love to buy some!