M*CARBO Brotherhood

Tool-less Locking Pin Install Can Be Easy

MCARBO sent me a new tool-less locking pin for the new recoilless charging handle I bought a month age, we are cool now, thanks. I watched the install video and could easily see why so many have problems getting the new pin into the spring assembly. Its like a spring loaded worm, difficult. I thought about it from a perspective of manufacturing, what would I design if I had a production line of multiples or single installs, obviously there would be no hands-finger’s on compression steps. From there I asked myself if I could simulate the mechanical spring compression for my one time install with simple materials lying about my shop. Yep. I built a spring compressor out of 3/8" ID copper pipe with a solid push piston of 3/8 PTFE Round Stock. All horizontally done on a piece of 2x6. The position of the first compression is easy to measure, and you want to lock that up as tight as possible to make the last step of clipping the pin into the springs 2-piece internal hairpins. Drilled a 1/4" hole in the copper pipe where one needs to put the temp compression holder, the 1/16" hex key with the kit, sharpen it to a point. Lay the tube assembly down on the 2x6 with a stop block screwed onto the board and push PTFE rod down the tube until the hoop end of the hair pin aligns with the drill hole in the tube, insert the 1/16 hex key, I had to tap mine in thus sharpening it first, then release the tension. Since this step is simple piston pushing a spring in a tube I drilled 1/8" holes in the board on axis, pushed the PTFE rod in with w piece of wood and stuck a finishing nail in the wood to hold the compression in steps, no strain on the fingers at all, zero. After the hex key is installed the compression is secured, remove the piston, pick up the copper tube take it apart at the threaded coupling and expose the split end of the hairpin, I had mine completely accessible, zero no finger strain, put the new pin on, remove the hex key, careful will have a bit of snap pack into place, remove it from the tube, inspect it closely on both ends and make certain the new pin and the stock pin are correctly in the pin holes and the spring hairpins are not twisted, they have to merge on recoil cycles and cant if they are twisted.
Took me an hour to build the simple assembly jig and 5 minutes to put the new pin in the recoil spring.

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I found the video of installing the locking pin was very difficult to install. I took a 3/4x4x6 board, drilled a 3/8 hole width wise 2 1/4 in deep. I clamped this in a vise, inserted the recoil spring, then used the same sized allen wrench to compress the recoil spring to where I needed it to be by inserting it through the spring, then inserted the small allen wrench that came with the kit to keep the recoil spring compressed. The only difficulty was holding the spring compressed while inserting the allen wrench to keep the spring captive.


Dennis, that sounds like a good method to install it. I doubt that I will ever have to remove the new pin, if I had to do them all day I wouldn’t want to do it that way I would want something with zero wear and tear on the fingers. I would speculate that if MCARBO makes at some point a complete package if charging handle and new loaded recoil spring that no sensible manufacturer is going to do it the one-timer way in their video. With the right compression jig, even a manual table top one, a tech could assemble a couple hundred in a day. Ideas like that have limited commercial value lifetimes, and impossible to patent. If it’s real good the OEM typically incorporates it into their standard model and then there is no aftermarket. Good job on thinking your way to a solution with what you had in hand, I admire ingenuity.


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Since you’ve already built the jig, how much for me to send you mine to install? My hands have way too much arthritis from dislocations and breakages to handle this…I tried.

Robert, at 68 I can relate to lifetime cumulative wear and tear, injuries, surgeries, the sum of a few scraps and can’t hear much after a lifetime around firearms and working in the industrial power generation world.
It would be my pleasure to fit a new pin into your existing S2K recoil spring, no charge at all then return it to you. Glad to be able to help. Below is my address and contact information. Don’t worry about return postage, I go to the Post office most days shipping someone something I am building or testing somewhere.

James Shinn
6203 Towhee Drive
Pinson, AL 35126

(205) 515-0383

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@Oneof6 I would delete that personal info from your post and private message Robert.


Hey i heard a guy over on MCarbo is doin them for free !!! @Oneof6

Dave, I give that information out in the form of business cards a hundred a week, I get so much junk email that more won’t matter and am able to easily say yes or no to just about anything. One could find out that much about me in 30 seconds on Google.
If someone needs a little help and I can I usually do. I don’t intend to make a dime on it and if MCARBO starts up the pin install for profit, or just doesn’t want members to help each other with it I will discontinue doing it at all, I have no intention of competing just helping.
I have my own small business training Engineers in Vibration Analysis, Large rotor balancing and gas handling systems trouble shooting. I do some traveling Service when things are going really wrong somewhere. And they need a disposable designated bad guy I am always building some gadget, simulator, instrument or mod for someone, both my hobby and occupation.