M*CARBO Brotherhood

90 Second Install Of the New S2K Integrated Spring Pin

Well I finished the second prototype yesterday and built the working install tool today. I changed my mind on going at it from a production standpoint to a common individual user tool that doesn’t require special tools to build cheaply or use easily. It can be easily used by individuals with hand back or neck problems. Its not tiny parts and big fingers torure. Without hurrying one can remove the stock Kel Tec spring retainer end and install the new MCARBO integrated spring charging handle pin that many seem to have trouble with … in 90 seconds or less of little effort. Wana take a break or answer the phone when you are doing it?, no problem you are not holding spring tension down with one hand manipulating the alignment pins and trying to twist on the new pin with the other, wishing you had help or another hand. Its a click click click self locking install device that you can set down and walk away from at any step. It sets up, compresses the spring tension exposes the last inch of the install side of the spring guide alignment hook as easy as pulling change from your pocket.
Cheap, materials cost less than 10 bucks. I built mine from stuff lying about my shop. If I was producing them I would likely make them out of extruded aluminum tubing but settled on Schedule 80 PVC for my uses and plan. I have no interest in marketing these installers, zero. I don’t care who makes one or a thousand (s). Feel free to take this idea and use it as is, modify it and improve upon it, its an idea gift to MCARBO members from me. I will still install the pins for Members that send their spring and pin to me, MCARBO seemed to be encouraging that on their video, but I really cant see much need as easy as this installer is to build.
One last thing, there always is one. Using this device compresses a spring creating stored energy, that stored energy if released, suddenly or inappropriately, can propel the spring assembly or the pin out. Used as is with a safety wire on the compression locking pin it cant. Treat it like what it is, the end of a barrel and keep it pointing away from you and away from others.
In the next few days I will clean up my sketches and compose a pdf of photos, the drawing sketch, and a materials list with tool required. PM me your email address and I will send it out to members as a group. Not depicted are two 1/16 X 2" pins.



Five Steps - 90 seconds to install.

  1. Install the center spring guide lock up pin in to the tool tube (center one with a witness hole and slot). Make sure that the pin goes through the spring guide not around it, it needs to be very close to the center where the two spring guides loop through each other.

  2. Install the tubes open end compression pin in the slot through the spring guide and into the tube compression slot all the way to the slot end. Make certain that the pin goes through not around the spring guide. Make sure you are good here, no sense in compressing it isn’t correct.

  3. Using the compression tool over the tube, align the two 180 slots on the compression tool open end on the crossing pin push it down to the second locking tab and elevate the compression tool to lock the pin in the lock tab. Secure pin down into the lock tab and bend it so it cant come out, a on time use safety.

Note… I still have hand strength to just hold the tube in my left and push the compression with my right. Its not hard at all because the compression tube is big enough hold with grip strength no pinch strength. As long as one can make a palm strike shape with one hand and push against a solid object with both hands they can use this tool idea successfully.

  1. Remove the stock Kel Tek spring guide pin holder, should be pretty easy and just might fall off

4.5 Install the new MCARBO Integrated Spring Guide and Charging Handle Pin. You will have about an inch of spring guide protrusion, its is no twisting magic trick, you wont even break a nail putting it on

  1. Use the compression tool to put some pressure on the locking pin, bend it out straight, use the compression tool tabs to unlock the pin and ease the pressure off.

5.5. Check your pin fit into the spring and spring guide, if good pull the center locking pin out, remove the spring assembly from the tube and you are finished.

Tip, before starting take a moment to study the spring and spring guide system. Understanding how it works and why one locks it up in the middle it to install this part is important.

Then, take another moment to read the steps noted above and understand each before using this tool idea.

Tip, taking the Kel Tek Pin out and installing the MCARBO pin is easier then putting the Kel Tek Pin back in, The Kel Tek pin doesn’t have the shoulder length to align itself into the spring body like the MCARBO pin does. It, the Kel Tek pin, tends to snap out of the spring guide when the pressure is applied unless its perfect. Then its a much more difficult job to get back to step one, maybe 5 minutes of product disparaging pejorative.

I use 16 gage 2.5" long finishing brads for pins. Reason, one use they do the job and are flexible enough to bend around the tube on the compression lock to make it a one time safety. I have a 5 # box and probably enough to lase until the end of time. There are many ways to safety this tool out when you have the compression applied and locked. Building this tool I lost count of the times I put it together and took it apart. I never had a pressure loaded pin jump out of the lock slot, but I built it and know what to look for. Now you do, safety that pin in the lock slot, a piece of soft copper wire looped around the back side pulling the pin in the slot would do the same thing as a safety, then one could use something harder for pins and put a handle on it, like a TIG torch element or even a hardened tempered wire pin, I wouldn’t use something more than .060" diameter.



Thanks for your design. Would it be possible to add a couple of close-up pictures of the tubes and explain how they are created? It would help the engineering deficient such as myself


It is my understanding that forum members can PM each other although I have not received a PM or sent one since becoming a member. I intend to share a dimensioned sketch / drawing, photos, parts materials list and tool list to build the installer. I will compile my shop notes and should have the drawing ready by mid next week. Then I will send out that pdf to anyone that PM’s or emails me requesting it. Free to any and all. I am almost always building some electrical or mechanical gadget, the fun for me is solving a puzzle, after that I get bored and look for something else to build.

1 Like

MCARBO should add an install kit as an option. I know I would have requested it. And my local gunsmith, that has worked on tons of S2K upgrades, would want one as well. I tried the install myself and cut my thumb up.

Great engineering James! I hope the powers that be are paying attention to the things the Brotherhood are doing for our addiction (I mean hobby). Lol.

1 Like

With this version #1 I thought that we could make something that works, is large enough for people with grip issues to grasp and use body weight instead of hand strength to engage the compression and a tension lock system to hold it while the operator changes the exposed spring guide area. And CHEAP as possible built from common parts with tools most have already. It isn’t sleek or pretty, it just works and has 10 bucks or less in materials. Mess up one building it, laugh about it and carve another.

I can think quickly of 5 different workable varients that would work as well, um better. Each with zero effort on the fingers. They would all require a bit of light machining to make, drilling, tapping and depending on varient milling and sleek enough/cosmetically attractive enough to appeal to customers as a permanent tool in the box worthy of a Brand or repeated daily use by professional Gunsmiths.

Where the first plastic working version has 10 bucks of materials and takes an hour or less to fashion … one of the metal devices would work a bit differently would have likely 50 bucks in materials and more than an hour, probably two, in light machining and assembly. They would have the additional feature of being safer with built in tension control.

I am three deep in ongoing industrial prototype models for my primary business and two for myself. If I get a few hours waiting on parts I will build one of the professional grade pin R n R tools.


Get BlueMail for Android

I just installed mine and although it took a little longer than 90 seconds it was no more than 5 minutes. The spring fit perfectly in the whole in my armorer’s block. The more spring I initially compressed the easier it was to install the connector pin. The Recoiless Charging Handle I took out did have a hole in it which I did not know and that was purchased before the first connecting pin came out but the recess below the hole was cut deeper than the new charging handle. The original Recoiless Charging Handle is shinier and more slippery than the new handle…I’ll keep the old handle as a spare.

1 Like


I’m curious. Do you think your tool makes install easier than @tinktrain1’s procedure? I think you either missed his post or see a procedural fault which hasn’t been identified. He describes his procedure here:

The Tinktrain Procedure

I ask because it seems you are working pretty hard. Tinktrain’s procedure works easily and does not require tool construction. I’ve honestly been expecting that @ChrisNelson will likely release an updated install video.


Dred, I am Marvin The Martian fan also.

Easier? that’s subjective depending on the person doing the RnR. For me, I had NO trouble at all using the Chris Nelson- MCARBO method, subject to my size, strength in my hands and substancial mechanical experience.

Others reported that they do have job stopping trouble, because of arthritis, hand injuries, neck and spine injuries and their general strength. Let’s don’t forget the females, few have hand strength to do the hold and pinch do the twist last step. The Ver 1 device I built out of simple schedule 40 PVC can enable those to with physical issues to do the RnR using their body weight against a table to set the lock and expose an inch of internal spring guide for easy last step of RnR instead of finger torture.

I can see the screwing the spring method working, mechanically, but not being a significant improvement for folks with the above listed physical issues. Acceptable mechanically, and the cheapest varient. I would have to do the procedure myself to opine on the safety issue inherent in situ with open spring compression of any kind.

The Ver # 2 I discussed in my last email would be a professional device more likely to be used by professionals like Gunsmiths and manufacturers making mod parts. This type of spring assembly with internal two piece guides is not uncommon, I like it for what it does. There are more out there than just the ones in the S2K bolt.

I could easily build one device that would work with any spring or spring with internal spring guides. Again, not a justifiable tool for most people. It would work differently than Ver # 1

I build a gadget model a day on average for fun, to improve something that interests me and or for profit sometimes in parallel with my business, which isn’t related to firearms, but involves precision machinery that often costs in the millions.

Some work out, some don’t, kinda like Wily Coyote and his Rocket Propelled Hammer. Most are functionally better than what is commercially available and often not viable because of my inclination to make more than just an acceptable device typical customization costd. Like my 144 Watt HEPA>UVC>Carbon HVAC whole house air sanitizer that costs me 950 to build, way oversized for most homes and un sellable. But fun to build.


Get BlueMail for Android


Nice work.

Installing that spring cap was the most difficult part of all the upgrades I did. I didn’t plan well when I started and ended up releasing the spring. Recapturing it completely was a challenge.

1 Like