[Chowwow]

Not sure why you chose to call me out specifically, but hey, whatever. You basically invited the following response by singling me out, so here it is:

Don't get me wrong, I didn't intent to call you out for anything, your name was the most recognizable that jumped out of my head and the old members of the forum are sure to drop their two cents on most of the topics around here. I knew people would rag on me for an obvious mistake and I just intend to be aware of my shortcomings and limitations.

You don't own an AR lower that you can cross measure to see the pin difference?.....which makes me wonder if you've actually shot one.

I have shot an M&P-15 but I obviously don't own one, otherwise I wouldn't have gotten so excited about jury-rigging a AR binary trigger into the XCR so soon. I don't intend to own more guns than I have fingers on one hand, and I've never been all that interested in the AR-15 other than a few components and its low cost. It was worth a rental on a range but not much more. It is why I settled on the XCR for its versatility and construction. It's still worth a close look.

Do you actually have access to the CNC equipment to do so?

If you must know about my boring backstory, I am in school to be a CNC machinist and I'm looking to start my apprenticeship real soon with local machine shops. That's why a lot of my solutions revolve use of CNC machines. So for the time being, I do have access to CNC machines that I have a reasonable level of competency and freedom with (reasonable as in not crashing while I operate them and freedom as in not making NFA items out of facilities not licensed for them). Might get tricky to be around one once I'm out of the school's machine shop.

I'm looking to get into making guns that are interesting to me, hence the study into the XCR binary trigger. However, if I don't find an easy solution to it then the idea will have to go in the back burner while I execute more low-hanging projects. Getting the dimensions to get the right timing on a trigger system is not something I've worked on ever. Adding an unreliable gimmick to a rifle that works fine semi-auto also makes this idea less of a priority. Still, I am interested in playing with the AR binary trigger, both in a FGC-9 build I want to do and, after learning from that, a specialized pistol.

 

[Sean K.]

Don't get me wrong, I didn't intent to call you out for anything, you're name was the most recognizable that jumped out of my head and the old members of the forum are sure to drop their two cents on most of the topics around here. I knew people would rag on me for an obvious mistake and I just intend to be aware of my shortcomings and limitations.


I obviously don't, otherwise I wouldn't have gotten so excited about jury-rigging a AR binary trigger into the XCR so soon. I don't intend to own more guns than I have fingers on one hand, and I've never been all that interested in the AR-15 other than a few components and it's low cost. It was worth a rental on a range but not much more. It is why I settled on the XCR for its versatility and construction. It's still worth a close look.


If you must know about my boring backstory, I am in school to be a CNC machinist and I'm looking to start my apprenticeship real soon with local machine shops. That's why a lot of my solutions revolve use of CNC machines. So for the time being, I do have access to CNC machines that I have a reasonable level of competency and freedom with (reasonable as in not crashing while I operate them and freedom as in not making NFA items out of facilities not licensed for them). Might get tricky to be around one once I'm out of the school's machine shop.

I'm looking to get into making guns that are interesting to me, hence the study into the XCR binary trigger. However, if I don't find an easy solution to it then the idea will have to go in the back burner while I execute more low-hanging projects. Getting the dimensions to get the right timing on a trigger system is not something I've worked on ever. Adding an unreliable gimmick to a rifle that works fine semi-auto also makes this idea less of a priority. Still, I am interested in playing with the AR binary trigger, both in a FGC-9 build I want to do and, after learning from that, a specialized pistol.

Didn't mean to pry....but needed a frame of reference.

JFYI, I've modded a LOT of triggers over the years....the factory XCR trigger is actually really pretty darn good. It could benefit from a polish job to make it smoother (or you can just let it wear in more) and I think the disconnector could have material added to it to make the reset travel in particular much shorter. I bought a spare disco to do exactly that...just haven't had time nor have I fired up the TIG.

If I still had CNC access, I'd cad up a new disco entirely as that's the better way to go versus welding....but you work with what you have.

I wish you much success and hope you can figure out how to make the semi auto part of a binary an excellent trigger. Just adding binary capability and leaving a shit trigger, to me is pointless other than for grins.....but I'm an admitted trigger snob. Once you have a really good trigger in a gun, you'll never compromise and want to go backwards, even for binary.

 

[Chowwow]

If I still had CNC access, I'd cad up a new disco entirely as that's the better way to go versus welding....but you work with what you have.

Still? You don't work in a place with CNCs anymore?

Also, what steel are triggers typically made from? There are desktop CNC machines that I can get for relatively cheap that mainly cut aluminum, but I don't know if I can rig one to machine 4140 alloy or anything tougher than high speed steel.

I figure making a binary trigger in the XCR is a decent enough idea in a time when machine guns are banned (I don't think even Robinson has an auto sear for it). Even so, I feel like the Binary Trigger is best suited for a cheaper platform in addition to your other arsenal and not your main rifle. I'd like to install one in the FGC-9 as a burst-fire PCC, then later into a compact burst-fire pistol; I'd get my money's worth in such applications.

 

[Sean K.]

Still? You don't work in a place with CNCs anymore?

Also, what steel are triggers typically made from? There are desktop CNC machines that I can get for relatively cheap that mainly cut aluminum, but I don't know if I can rig one to machine 4140 alloy or anything tougher than high speed steel.

I figure making a binary trigger in the XCR is a decent enough idea in a time when machine guns are banned (I don't think even Robinson has an auto sear for it). Even so, I feel like the Binary Trigger is best suited for a cheaper platform in addition to your other arsenal and not your main rifle. I'd like to install one in the FGC-9 as a burst-fire PCC, then later into a compact burst-fire pistol; I'd get my money's worth in such applications.

Nope. We farm out most of our CNC work here. We have manual mills and lathes for prototyping but I'm not a skilled machinist....just a hobbyist at best.

RA has auto sears....they used to be (dont' know a current status) a SOT.

 

[Hartman23Foscari]

Interesting idea, actually. You think the dimensions on the upper would change much if they serialized it? Are we on the 3rd revision of the XCR right now? Maybe the next revision they could serialize both the upper and lower, so that if you don't get a complete rifle from RA, you could build around it with their parts. A shorter lower ought to be an advantage for some AR-15 builders, and having unified uppers are a premium AR product - it's sure to be competitive when LMT has got it hands busy.


Fascinating. With luck, it's possible that all you would need to do is CNC machine a hammer that's compatible with the XCR and drop it into the binary trigger. I really need to examine a binary trigger though, because I don't know if there is something about the hammer in it that helps with the binary fire function. I think I'll get one just to examine when my budget is able to breathe.

something that would be truly interesting to see, if they wanted to go with a shorter lower. They should make the step striker fired, ala vz58. the vz58 is lighter then a stamped ak yet is milled because its lighter weight. It would allow them to make a truly short system since the striker does all the work and the trigger just releases it.

hell ive had the idea for somehow taking a vz58 style lower with an ar style upper with a piston driven system. Would be the ultimate gun advancement imho.

 

[Sean K.]

something that would be truly interesting to see, if they wanted to go with a shorter lower. They should make the step striker fired, ala vz58. the vz58 is lighter then a stamped ak yet is milled because its lighter weight. It would allow them to make a truly short system since the striker does all the work and the trigger just releases it.

hell ive had the idea for somehow taking a vz58 style lower with an ar style upper with a piston driven system. Would be the ultimate gun advancement imho.

Yeah, but the trigger is sub par in the VZ comparatively.

 

[Hartman23Foscari]

Yeah, but the trigger is sub par in the VZ comparatively.

I found the trigger to be quite usable and it is a trigger from 1958.... im pretty sure with modern tech we could make it better.

 

[Sean K.]

I found the trigger to be quite usable and it is a trigger from 1958.... im pretty sure with modern tech we could make it better.

Meh, I have serious doubts it would ever equal a modded AK trigger...or a decent AR one for that matter.

 

[Parchaser]

Ok, so thanks to this Youtube video we have a more in-depth look at the Frankin Armory Binary Trigger. I fully suspect that the hammer of the XCR trigger is shorter than that of an AR, and the gentleman in the video states that the secret in the binary trigger sauce is mainly in the trigger itself, the hammer is pretty much like an AR hammer. Two issues. First is a major issue, I'm concerned that the XCR trigger is also low profile and the binary trigger would sit higher than it. I don't think RA would reinvent the wheel and I suspect the seat where the trigger sits and the safety location are similar to an AR trigger group. A second more minor issue is the fact that the XCR, of course, does not have a buffer tube, while the binary trigger package includes a buffer tube spring. I believe this spring is specific to help the binary trigger reach its timing as the BCG moves over it to achieve binary fire. The stock recoil spring in the XCR may or may not cause issues with binary trigger action; it's the disconnector hook on the trigger that's the primary actor in the binary function and that can be adjusted according to the specific system.

I'm going to get some measurements on the trigger in the XCR vs a typical AR and see if there are any differences in height. If I get a good feeling about this, I'll try getting a binary trigger from my local gun store and see if I can get it to work. I suspect that I can use the stock XCR hammer and just use the trigger, disconnector hook, and safety switch in the Binary Trigger package, leaving out the buffer tube springs. I always wanted to use the binary trigger for something but, long term, I want my XCR to stay semi-auto as Robinson made it. I just hope this kind of discovery would help alleviate the chronic, terminal boredom I see on this fan base.

Franklin made a binary trigger pack for the Bushmaster ACR and Ruger 10/22 neither which has a buffer tube. How many ACRs were made vs how many XCR's?

 

[Chowwow]

How many ACRs were made vs how many XCR's?

At least thousands more, considering the rate the Robinson makes their rifles and that the other has been out of production for about a year at least. But if you are thinking what I think you are thinking, I would advise against it. The ACR trigger comes in a pack while the XCR's is housed in the lower like an AR-15 is, which indicates to me that the parts inside the ACR trigger pack aren't meant to function outside of it; so even if we took the parts out there's no telling if they would still line up with the XCR's trigger system. Furthermore, I've examined enough AR-15s to know that the pins don't line up with the XCR's, and even if we could install the trigger parts in the correct order, they probably won't contact or line up with each other enough to function. As of now, the only way to install a binary trigger into the XCR (as it is) is to design one specific for it. Just because the binary triggers share the same concept doesn't mean they share the same design, as the different models Franklin sells for different firearms indicates.

Instead, a more worthwhile project is to design a lower receiver that retains the XCR's magwell and bolt catch parts (and stock adapter, maybe) and blends in an AR-15 trigger group and pistol grip (and maybe trigger guard) that mounts with the regular XCR upper. All one has to do is super impose the dimensions of the AR-15's trigger system onto the dimensions of the XCR's receiver, then print it out on a 3D printer. Something like this solves/provides many issues/needs that people have with the XCR: it allows for compatibility with aftermarket triggers (not just the binary trigger but those Geissele triggers people are crazy about), offers a polymer (ABS or glass-reinforced nylon) lower option that might save weight, and provides an unserialized lower that you can have on a rainy day (Biden willing).

The dimensions for the AR-15's lower are widely available, the trouble comes with getting the dimensions of the XCR's lower (I can measure mine but having official measurements from company prints would help a lot). I'm also having trouble deciding on what to do with the stock adapter; the XCR's stock adapter is pretty simple and actually pretty solid, but I don't enjoy the FAST stocks that RA makes. I'd like for an XCR lower to be compatible with the ACR stock out of the box, but the adapter that comes with the ACR stock is very obtrusive to the inside of the XCR. I'm thinking of doing a mini picatinny rail on that spot similar that Sig Sauer uses for the MCX line. It's actually pretty versatile; you can then have a mini or pistol length XCR without having a cap for it, then mount Sig's line of stocks if you want or get that ACR stock adapter that attaches to picatinny rail.

I'm in the early stages of another project that I want to do for the XCR and considering my productivity, I wouldn't hold your breath about me getting this out anytime soon. However, I'm surprised that something like this hasn't been done before like it has for the CZ Scorpion et al. Still, unless there are any objections, an AR to XCR lower is something that would really be worthwhile.

 

[Sean K.]

At least thousands more, considering the rate the Robinson makes their rifles and that the other has been out of production for about a year at least. But if you are thinking what I think you are thinking, I would advise against it. The ACR trigger comes in a pack while the XCR's is housed in the lower like an AR-15 is, which indicates to me that the parts inside the ACR trigger pack aren't meant to function outside of it; so even if we took the parts out there's no telling if they would still line up with the XCR's trigger system. Furthermore, I've examined enough AR-15s to know that the pins don't line up with the XCR's, and even if we could install the trigger parts in the correct order, they probably won't contact or line up with each other enough to function. As of now, the only way to install a binary trigger into the XCR (as it is) is to design one specific for it. Just because the binary triggers share the same concept doesn't mean they share the same design, as the different models Franklin sells for different firearms indicates.

Instead, a more worthwhile project is to design a lower receiver that retains the XCR's magwell and bolt catch parts (and stock adapter, maybe) and blends in an AR-15 trigger group and pistol grip (and maybe trigger guard) that mounts with the regular XCR upper. All one has to do is super impose the dimensions of the AR-15's trigger system onto the dimensions of the XCR's receiver, then print it out on a 3D printer. Something like this solves/provides many issues/needs that people have with the XCR: it allows for compatibility with aftermarket triggers (not just the binary trigger but those Geissele triggers people are crazy about), offers a polymer (ABS or glass-reinforced nylon) lower option that might save weight, and provides an unserialized lower that you can have on a rainy day (Biden willing).

The dimensions for the AR-15's lower are widely available, the trouble comes with getting the dimensions of the XCR's lower (I can measure mine but having official measurements from company prints would help a lot). I'm also having trouble deciding on what to do with the stock adapter; the XCR's stock adapter is pretty simple and actually pretty solid, but I don't enjoy the FAST stocks that RA makes. I'd like for an XCR lower to be compatible with the ACR stock out of the box, but the adapter that comes with the ACR stock is very obtrusive to the inside of the XCR. I'm thinking of doing a mini picatinny rail on that spot similar that Sig Sauer uses for the MCX line. It's actually pretty versatile; you can then have a mini or pistol length XCR without having a cap for it, then mount Sig's line of stocks if you want or get that ACR stock adapter that attaches to picatinny rail.

I'm in the early stages of another project that I want to do for the XCR and considering my productivity, I wouldn't hold your breath about me getting this out anytime soon. However, I'm surprised that something like this hasn't been done before like it has for the CZ Scorpion et al. Still, unless there are any objections, an AR to XCR lower is something that would really be worthwhile.

A pic rail mount has been made in the past.....Nate (@navalbeaver) has at least one. Can't remember who makes it off the top of my head.

As for the rest of it, I think the AR lower is narrower than the XCR.

 

[Chowwow]

As for the rest of it, I think the AR lower is narrower than the XCR.

Right, I think I heard you also say that it was like .25" taller than the XCR lower too? The narrowness is not a big deal but the most important part about this project is positioning the hammer of the AR trigger to land just right on the firing pin of the XCR upper. The hammers are not alike either and I don't yet know what's the right point where the hammer lands that makes a good pin strike (i.e. is it the apex of the swing, just at the end of the swing, or where the face of the hammer makes a 90 degree angle with the head of the pin?). I'll also have to make sure there's enough clearance for the top of the hammer so it doesn't get caught by the XCR's bolt. The relative height of the trigger group should feel seamless if a bit taller than the original, but I want to do this without having to make a longer bolt catch or making the magwell too deep; I don't want to mess with the magwell and bolt catch's dimensions or make new parts for them.

While I'm at it I may as well as make the lower compatible with the AR's auto sear for the intrepid SOTs out there. Regular semi-auto trigger groups still fit, as I understand it, and we are still not making an automatic XCR because there is no automatic bolt group publicly available and the dimensions of one are a mystery to me. A useless feature but, eh, may as well?

 

[navalbeaver]

Right, I think I heard you also say that it was like .25" taller than the XCR lower too? The narrowness is not a big deal but the most important part about this project is positioning the hammer of the AR trigger to land just right on the firing pin of the XCR upper. The hammers are not alike either and I don't yet know what's the right point where the hammer lands that makes a good pin strike (i.e. is it the apex of the swing, just at the end of the swing, or where the face of the hammer makes a 90 degree angle with the head of the pin?). I'll also have to make sure there's enough clearance for the top of the hammer so it doesn't get caught by the XCR's bolt. The relative height of the trigger group should feel seamless if a bit taller than the original, but I want to do this without having to make a longer bolt catch or making the magwell too deep; I don't want to mess with the magwell and bolt catch's dimensions or make new parts for them.

While I'm at it I may as well as make the lower compatible with the AR's auto sear for the intrepid SOTs out there. Regular semi-auto trigger groups still fit, as I understand it, and we are still not making an automatic XCR because there is no automatic bolt group publicly available and the dimensions of one are a mystery to me. A useless feature but, eh, may as well?

Rumor the forum, Alex wanted a shorter lower. It would have to have been about .25" taller to work with an AR trigger. I think someone squeezed in a cmc(?) trigger into a xcr way back but it took some machining. I haven't looked in a long time but I thought the layout/spacing on the pins and safety were pretty close to the AR pattern. Larger barrel on the xcr safety.

You'll have to figure out how you want to deal with the extra height. Whole lower is taller/just move the trigger group etc. I'd bet a decent amount the center of the trigger, hammer and safety holes are the same as an AR FCG. Again, that's eyeballing without actual measurements but why re-invent the wheel. I'm not willing to pull a trigger pack to check lineup at the moment. Measuring from the top of the lower/bottom of the upper to the firing pin should be pretty easy to figure out where the hammer strikes. RA has 3 pin lowers for the Machine Guns. Not sure if there is a specific auto BC.

 

[Chowwow]

Coming back to this thread to go over what I found when trying to install an AR trigger group into the XCR-L lower. Since the binary trigger is basically the same dimensions of a normal AR trigger, I decided to try using a cheap mil-spec trigger instead of a $400 binary and install that into my lower. Some of you may have already known what I'm about to say but this hasn't been documented before, so here it is for future users. TLDR: Not gonna work.

First, a look at the XCR lower:

So we know RA made the lower, well, lower than a typical AR lower, probably to make it sleeker and compensate for the height of the gas piston on the upper. Pin locations appear to be the same but without specific dimensions, I can't be sure. Before installing anything I put the AR trigger on top to simulate how it would fit:

The trigger and pins seem to match. Disconnector about the same height as the original XCR. Hammer is taller by about .29" and seems to be a bit too far back to make a 90 degree strike face with the firing pin. Not too bad considering that the bolt has more height space for the hammer to hang over before hitting the recoil spring, but there is more.

I put the trigger into the trigger well to see how it could fit. Pic has the trigger closer to the camera so the relative size is exaggerated, but there is clearly a bulge over the safety selector that's normally holding it down but in the way of the trigger. Nothing an endmill can't fix right? Well, the bigger issue is that the AR trigger's disconnector is along the center of the group instead of off to the left of the group like the default XCR trigger is. This imposes a hard limit to how low the hammer can go (along with the hammer's top crest of course). Why is that important?

Here is how the default hammer positions itself during the middle of the firing cycle when the bolt is traveling over it. I noticed how the hammer's face and the bolt carrier's bottom had linear scrapes over them; it's because the bolt carrier forces the hammer down to where the bolt is almost in line with it, making it much lower than when it's hanging cocked. An AR trigger cannot go much lower than it already has when cocked.

In the above picture, the sears are about in line with each other. Even at it's lowest, the AR trigger is still higher than the XCR trigger when cocked - and even that is too high. The magic number to all of this is .29", that's about the difference between the height of the lower and an AR lower, how much clearance the bolt carrier has over the top of the lower, and how much taller the AR hammer is versus the XCR hammer both released and cocked.

After this I decided to abandon the install; even if I could force the FCG to fit into the XCR magwell, even if I could make the hammer fire, the hammer would just get caught under the bolt carrier and the rifle won't even be able to extract, much less cycle and fire again. At this point there are two options to get binary fire on the XCR: design a new lower for the XCR that fits AR triggers or design a binary trigger for the XCR FCG from scratch.

 

[Sean K.]

The training scars binaries impart make them wholly undesirable IMO. They are range toys and that's it. Again, JMO having owned/played with them. Lots of fun, not very useful from a self-defense or offense perspective.

 

[Chowwow]

The training scars binaries impart make them wholly undesirable IMO. They are range toys and that's it. Again, JMO having played with them. Lots of fun, not very useful from a self-defense or offense perspective.

I understand. But beyond just the binary trigger, are there AR-15 triggers that you wish could be installed into the XCR? Something from Timney or any other high-end manufacturer? Didn't you want a single-stage trigger at some point? I don't see much of a trigger aftermarket with the kind of market penetration the XCR has right now.

 

[Sean K.]

I understand. But beyond just the binary trigger, are there AR-15 triggers that you wish could be installed into the XCR? Something from Timney or any other high-end manufacturer? Didn't you want a single-stage trigger at some point? I don't see much of a trigger aftermarket with the kind of market penetration the XCR has right now.

Do I wish the XCR had the same amount of trigger options as an AR? Of course, options are a good thing. I'd love a very short travel, single stage trigger with a fairly light pull. However, the factory 2 stage isn't bad at all...very similar to the old standby SSA.

But, as you can see, it's not a drop in. Best bet (for me) is to mod the factory components (much as I do an ALG for an AK). And it would just be a 'nice to have'....not a necessity since the factory trigger (once properly broken in and smoothed out) is damn good for a factory trigger.

The bigger problem is that the XCR is a niche gun. There aren't a lot of them even in circulation...what? Less than 13K XCR-Ls. So it's unlikely any mainstream trigger manufacturer is going to make them. Hopefully the advent of 3D printing will result in a small 'hobby shop' XCR enthusiast building something. Or someone with access to traditional milling equipment for that matter....

 

[Sean K.]

Hmmm...I wonder if the XCR's modularity keeps the sales figures lower than they otherwise would be. I know most here just buy entire new guns....or at least uppers rather than just conversions, but I'd think that would at least account for some loss in sales of full up weapons.

 

[Chowwow]

Well, what does the average gun consumer thinks is modular? The XCR lets you put any optic, lights, accessories, grips, etc on the rails; for a lot of people, that's modular enough. It's kind of a hassle to get different stocks for it but there are solutions available. The final frontier is triggers, and how many people really want to mess with that? I figure the portion of people who like to tinker with the internals of a gun are like those who like to tinker in their cars or computers; a minority of a minority. If RA really wants to make the XCR popular and catch people's attention, instead of more options, it would need better marketing. Have John Wick own a building full of goons with an XCR and finish off the big bad guy by clubbing him to death with the rifle's metal body. Have the next Stargate series feature the XCR being taken off world to shoot the heads off some aliens when they hide behind their energy shields. Most important: have the XCR be represented in Girls' Frontline as a hot chick in an interesting, sci-fi military garb that players earn by playing the game. Robinson Arms will become immortal after that!

 

[Sean K.]

Except they can't fill the orders they have in a timely manner.