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Discussion Starter · #1 ·
I'm offering this up as a step-by-step guide to a solution I cooked up for M4 stocks. What each person chooses to do, from simply throwing a screw in it, or epoxy glue, is up to them- however, I am posting this because I believe it has several advantages:

1) Removal of the screw will NOT allow the stock to be collapsed or extended. This is because the plunger is still locked in place by spring pressure.

2) Not relying on super glue or epoxy means it can't be shocked loose (slamming trhe rifle butt on a table will not make it into a "collapsible stock".

3) We have seen a wave of prosecutions over "evil features" including a video released by Nassau DA's office that was edited to appear to incriminate the defendants. This gives me (and should give all of us) very little faith that our "pinned" stocks that can get the pins pushed or tapped out offer us protection under the current administration's interpretation of the law.

4) This can be disassembled and replaced without destroying the buffer tube. Removing the buffer and drillling a small (1/16") hole in the top of the buffer tube allows a wire to be inserted to depress the plunger from the top and allow disassembly of the stock.

OK so without further ado, this is the method I came up with, step-by-step:


Pictured above are the original components of the factory stock, disassembled. In addition to the activation lever there is a plunger, a spring, a bushing, and a pin.


The bushing and pin will go in the spare parts box, we will be substituting a 1/4x20 hex head stainless steel machine screw.


Assemble the stock and measure how far the threaded part of the plunger protrudes from the stock.


This one extends 6.64mm.


Measure the length of the shank of the machine screw.


I got 16.18mm :)


Time for some rudimentary mathematics:
(length of stock plunger) - ( length of plunger 'stickout' + length of machine screw shank) = length to cut plunger.


Mark and cut off plunger, dress end square with a file.


Here are the modified plunger, the spring, and the machine screw. The section that got cut off the plunger gets thrown away.


Use a soda straw to hold the spring and plunger assembly together so you can insert it into the stock from the top.


You need to "block off" all of the holes REARWARD of the position you want the stock to be "fixed" in. This keeps the plunger from snapping into the wrong hole. I used aluminum duct tape wadded up in the hole with another couple pieces over the top.


use a screwdriver from the top of the stock to depress the plunger and slide the stock onto the buffer tube. when it gets to the first available hole that you have not plugged, the plunger will snap into place. The stock is now a fixed, non-telescoping stock.


Here is the spring from the bottom, there is no longer any way to retract the spring since we cut the bushing end off of the plunger.


BUT for the sake of cosmetics, we want to attach the lever back. This is where the 1/4" machine screw comes in.


You can thread the stock hole for 1/4"x20 thread, or you may be able to simply screw the machine screw into place with a little muscle if you don't have a tap- it's only going into plastic.

That's it! Hope this was helpful!

Also, because I don't know where to put it:

This is an "evil feature" A2 flash hider...


you can use this YHM comp and drill at the location shown, then insert the back of the drill bit, cut it off with a Dremel, and weld into place. Drill rod is hardened steel, trying to muscle it off with a wrench will surely remove the "evil" threads from the soft barrel. This is really about all most of us can do on a stainless barrel. I used two pins.
 

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You Are the Resistance.
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I like the stock fixing method-

Myself, I might pre drill the receiver extension ('buffer tube') and stock at each detent position, so I could later change LOP or disassemble without a drill press. this would also remove the need to block off the detents behind the one selected.

As to the second, does that Compensator install over the A2 unit, or does it have to be removed first?
 

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Discussion Starter · #4 ·
Sorry Ramoone, you have to remove the A2- my Palmetto upper arrived with the A2.

You could predrill the upper- but that also means the cops with a paper clip can "collapse" your stock- so I guess it depends how paranoid you are. i'm pretty paranoid.. :)
 

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Very nice writeup, and I love the pictures.

I recently just pinned my MOE stock for my AR build.

Just put her into position in a vice, used a drill press to drill a hole just under the diameter of a wire coat hanger, and drilled through with a small clearence so I didn't poke through into the tube.

(If I wanted to have her any farther out, I would have had to fill the holes, which meant hitting up the laser cutter and making some aluminum or polycarb inserts, and a lot more dimensioning and fitting, which I wasn't really feeling at midnight.)

Anywho - Superglue + epoxy to the areas touching metal and plastic respectively after I cut her, and then forced it in there.

Now she's fixed in place at a decent length (for me at least), and I didn't have to dick with the actual locking mechanism at all.

To double check that this was savvy, I ran a shear stress/strain analysis on a mockup I did on my computer and it is going to take a lot more than shooting a .223 round, or even dropping the rifle directly on the stock from 10ft high to break the pin.
 

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Bangkok rules. Now who has a can?
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Great post Captain!  Thanks!
 

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Discussion Starter · #7 ·
deathsythe said:
, I ran a shear stress/strain analysis on a mockup I did on my computer and it is going to take a lot more than shooting a .223 round, or even dropping the rifle directly on the stock from 10ft high to break the pin.
OK, now slam the butt into a concrete slab. The problem with computer mockups is that they are only as good as the data you feed them.... do you know how to calculate how much force that pin is subject to the "old school" way to figure the KE?

3m drop at 10m/s/s nets 7.7m/s * 4KG rifle = 117nm, if it stops in 1mm (concrete) then 117Kilojoules! That's like, 86 THOUSAND lbf!- do you think a 3/16" pece of coat hanger wire embedded in some plastic is not going to yield?

Even the stock plunger I'm using is probably going to damage the 7075 tube. You could pour the stock full of urethane rubber, which would help with stability and probably not "let go" the way epoxies or super glue can, because urethane is very resilient and the bond is tenacious- but it's also very expensive. I have a gallon of the Forsch stuff, which is about 90 durometer,cost me about $150 and has a six month shelf life.

Anyway, my point in computer simulations is that you need all of your materials properties and other parameters to be correct, and even then sometimes they don't work. I made several flywheels for a project and had them each fly apart (scary!) even though the finite element analysis said they were well within design parameters at 70%. Turned out there was a harmonic transmitted through the assembly's dynamic balance in the "real world" that was not taken into account by the computer- at least that's what I THINK happened- coulda been the computer was trying to kill me, I guess I'll never know!

If "rough handling" at the crime lab consists of taking a 10" wrench to your brake or having Sgt. Noneck slam the rifle on the floor to "test" it a dozen times, I want PHYSICAL DAMAGE to the FACTORY parts to be evident! But like I said, it's up to the individual. If the pin can be removed or defeated without tools and without destroying the stock though, IMO that could be a liability. I'm not saying yours is. I'm just saying don't trust a computer mockup. (Unleess you are an engineer or knowledgeable and just using the computer to double-check what you already determined).
 

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BE and ME in Mechanical Engineering.

But I get ya, thanks for looking out. :)
 

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Good Post!  Can never be too careful!
 

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Your'e asking for trouble with the "fixed" collapsing stock. Buy a manufactured permanently fixed "look alike" collapsible stock or a full size fixed stock.
 

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Zombtac Operator
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fredw said:
Your'e asking for trouble with the "fixed" collapsing stock. Buy a manufactured permanently fixed "look alike" collapsible stock or a full size fixed stock.
Bushmaster factory NY Compliant (Post/Perm Brake) M4 stocks are just blind pinned and epoxied (nicely done but they are pinned nonetheless).
 

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The Artist formally known as AR_Guy
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Destro said:
Bushmaster factory NY Compliant (Post/Perm Brake) M4 stocks are just blind pinned and epoxied (nicely done but they are pinned nonetheless).
Not unless they changed the process. The Bushmasters are built on Rifle length receiver extensions. No detents for a moving stock, it just looks like it. But yes it's pinned, but on a different set up entirely.
 

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Team Kalashnikov
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Thank you for this post, Not going to do it your way but plan on pinning it this weekend.
& I'll be dammed if someone thinks they will come and slam my s**t on the floor to see if it's fixed enough.
But let's say that was the Case, even if it's a really weak pin the stock shouldn't collapse in hittingthe ground unless
The Spring is released. They would have to hold spring open and slam on floor simultaneously In order to prove strength of pin.

Destro said:
Bushmaster factory NY Compliant (Post/Perm Brake) M4 stocks are just blind pinned and epoxied (nicely done but they are pinned nonetheless).
That's what I dont get, my NY complaint rifle stock came from smith and wesson w a Pinned stock.
Right through the side. Looks fairly breakable/removable. I don't see why I could not Pin my own in a stronger fashion and it not be legit?
 

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tagged thanks capt'
 

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Did one stock today based on this method. Worked great/
I used .30 cal gas checks on the buffer tube notches to fill them and prevent the stock from "snapping" into the wrong hole.
It was fairly simple. there is an ever so slight wiggle in the stock. However by no means is this thing moving.

Thanks again Captain WILL

My next step is assembling the lower. time permitting
 

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Discussion Starter · #16 ·
The wiggle in the stock is inherent in the stock design, it does not fit tightly on the buffer tube. Now that the stock is fixed in place, you can use a little silicone or practically anything else smudged between the buffer tube and stock on the front and back ends to stabilize and prevent the "wiggle"

I used 90 durometer urethane on one and it's solid as any fixed stock.

I found that wiggle annoying too and it's hard to imagine that does NOT affect accuracy to some degree, but every USGI with an M4 has to deal with it, and ssem to take it in stride.
 

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Hey Capt.
You think, under the current law, this is even necessary anymore?
If someone where to buy a new stock that isn't pinned....would they have to pin it under the current law?



Had to add teh smiley
 
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