MCM A5 stock w/Thumb wheel cheek problem UPDATE!

USMCj

USMCj

Gunny Sergeant
Full Member
Minuteman
May 1, 2008
4,053
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44
Nazzifornia
#1
Hey guys, Im having a bit of a problem with my A5, I contacted Ryan over at MCM and he was real nice about it, but he needs the stock to be sent to him to get fixed, and since money is tight and I really dont want to ship the stock out. I thought I would ask and see if anyone els is having the same issue, and maybe there is an easy fix without sending the stock out.

Every time I got shooting, after abotu 3-5 shots, the thumb screws on the right side work loose, no matter how tight they are. I really dont want to use loctite. Anyone els with the same issue? any easy fixes?



<span style="font-size: 14pt"><span style="color: #FF0000">UPDATE:</span></span>

I belive I found a solution, and I thought I'de share. The reason the cheek piece becomes loose under recoil is because the posts on the cheek piece are aluminum and the thumb screws are steel, but the problem is the thumb screws are pointed, much like a punch, so there is not a whole lot of contact area making them dig into the aluminum and create play.

Solution? increase the contact area of the thumb screws by grinding the pointed tip to a nice square/flat tip. Pics below show the difference.

IMG_0296.jpg


IMG_0297.jpg


IMG_0298.jpg


Having increased the contact area by like 500%, and the thumb screws no longer acting as a punch, this should stop them from digging into the aluminum posts (in theory at least
laugh.gif
)
 
#2
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

havent had the problem you describe, but could you drill 2 holes through the bar attached to the cheekpiece and some how thread a screw through the hole so its locking the piece into place persay?
 
#3
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Mine don't work loose that quickly, but they do eventually come loose. I just always check them and tighten them down again every so often. Someone else may have a better solution, though.
 
#4
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Nahh, thats way too much, lol. I could loctite the thumb screws and get the same effect. But I need to lower it to remove the bolt, so I need it to not be so permanent.
 
#5
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

I have 3 McM a5's with the hardware you have, 223, 308, 300WM. the 223 doesn't work loose at all, the 308 will work loose but after a few rounds, the 300WM will work loose after about 10 rounds though. I have even tried dimpling the aluminum studs that the screws set against to see if that would help the only thing it really helped with was repeatability of getting my cheek piece back in the same place. I have thought about just switching over to allen head screws so I could get some gusto on em and maybe they would stick then but who knows no more than I shoot I can live with it.
 
#8
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

I was thinking of using weaker than blue loctite, maybe green or purple. The way Loctite drys, it still offers some resistance after repeated usage.
 
#11
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

I think part of the problem is that the aluminum gives a bit which allows the screw that little bit to loosen up which goes downhill from there.
 
#14
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Hmmm, I wonder, what if I remove it, then drill and tap the aluminum holes and use steel thread repair coil (not sure what they are called.

found a pic of what Im talking about.
41BbNvfQa0L._SL500_AA300_.jpg


now does anyone know what the thread pitch is on the thumb screws?
 
#15
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

In case I wasnt clear, I want to use the thread repair coils which are made out of steel to repair the holes the thumb screws go into, which is aluminum.
 
#16
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

I used to have the same problem with my Mcmillan M3A stock cheek piece.
I found the solution was to cake the threads up with blue locktite.
It made the thumb screws harder to turn, but not impossible, and certainly not permanent.
 
#18
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

But from the sound of it, no matter what I do, its going to be a band-aid fix because the aluminum threads are going to give in more and more, so I think the best thing to do is to repair the threads with steel repair coils.
 
#20
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Use the 'Heli Coils', but make sure you know how to do it correctly.
Drill SQUARELY into the hole with the bit supplied in the kit. Use the supplied tap to cut the new threads into the aluminum. If it's not supplied with a bottoming tap, the supplied one will be fine. Now using a Q-Tip, put a light coat of loctite(RED) on the new thread insert and use the tool to put it into the freshly tapped hole. Let it sit for 24 hours to cure.
You should now be able to use the threads, but overtorquing them will only serve to move the new heli coils in the aluminum.

A Thought: If you want them to hold tighter, you may want to try using a bottoming insert(allen screw) to place pressure on your set screws to stop them from moving.
 
#21
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMCj</div><div class="ubbcode-body">Dont know how much it would help, but it would have to be a thich ass wacher, lol.</div></div>
Got it, I thought it was a loosening issue, not a metal issue.
Coil seems like the "best" solution. Does McMillan have a solution for you or are the just fixing to the same thing? If solution, hell, give it up for a while to get it fixed.
Good luck.
Chad
 
#22
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Thanks guys, but the heli-coil idea is not going to work. It looks like they bedded the aluminum block into the stock, and even after taking off the screws that hold the block down, it wouldnt budge.

Loctite it is I guess.


Switch, thanks, used heli-coils a whole lot on my motorcycle for thread repair (aluminum frame
laugh.gif
)
 
#23
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Watching this thread like a hawk....
wink.gif


I currently have an A3 and mine are always coming loose. I just thought it was the nature of the beast and not broke. So, I just got in the habbit of always checking them. In fact you made it sound like the McMillan guy hadn't seen the problem before and he needs to look at it to fix it (maybe that's not the case but that is how I took it). I highly doubt that only a few of us are seeing the problem. It has to be well known. Like I said, it doesn't seem broke it just seems "under-designed"....is that a word??
grin.gif
 
#24
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

I just realized something. I dont think its the threads thats the problem, but the posts that the thumb screw tightens down on. They are made of aluminum and the thumb screws being steel and pointed, dig into the posts rather easily.

This has to be it, because my AICS had the same thumb screws yet it never worked loose, I think its because the posts were steel on the AICS cheek piece so the screws were not able to dig into them and create play.
 
#25
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

I thought McM changed the hardware for that reason. Maybe I misunderstood but this was the post from Dick Davis.

"Also, for those who caught my "clamp bar" reference above, at the first of this year we changed our standard intergral cheekpiece riser from the old cylinder and post with two thumbscrews to a clamp bar on the two posts with a single center screw. It is basically similar to the KMW unit but uses our standard cheekpiece riser so the lateral adjustment is accessible from the top of the cheekpiece like it always has been. It is still ambidexterous, and the clamping parts inside are just two stainless 1/4x20 square nuts, one with the threads drilled out, that are replaceable from any local hardware store if you lose one. Also, the thumbscrew can be replaced with a standard 1/4x20 socket head cap screw 3/4" to 1" long available at said local hardware store if you don't want the thumbscrew protuding from the side of the butt.
We used our old system for many years with not too many problems, but with more and more of the big magnum calibers being used we were getting more complaints. We finally figured out that with the sharper heavier recoil impulse, the aluminum post was deforming where the point of the thumbscrew was bearing on it. You could tighten it up and in a few hundred rounds the aluminum would start to deform and get loose again. The clamp bar system has been around since the horse and buggy days and seems to be bullet proof against metal deforming and getting loose."

If you mail it in, they might just change out the hardware for you.
 
#26
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

I saw that too, but I think he was talking about the standard versuion and not the thumb wheel adjustable cheek piece.

I think the one he is talking about is this one, they replaced the 2 thumb screws to 1 and a clamping system instead of the thumb screws touching the posts

Adj-lockscrews.jpg


But I have this one

Adj_thumbwheel.jpg


now unless they have designed a new thumb wheel unit that clamps the posts, the above doesnt help me.
 
#29
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Please let us know what McMillan tells you, as I have the exact model that you have.....




<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMCj</div><div class="ubbcode-body">I saw that too, but I think he was talking about the standard versuion and not the thumb wheel adjustable cheek piece.

I think the one he is talking about is this one, they replaced the 2 thumb screws to 1 and a clamping system instead of the thumb screws touching the posts

Adj-lockscrews.jpg


But I have this one

Adj_thumbwheel.jpg


now unless they have designed a new thumb wheel unit that clamps the posts, the above doesnt help me. </div></div>
 
#30
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Here is the fix: elevate cheek where you need it to be, tighten one screw, take other out, take pencil tip or pen and mark aluminum shaft in open hole, take cheek piece out , file notch for screw to seat into, put back on, lock screw into notch and do other side.

I also replaced my thumb screws with round-head alan screws from hardware store, and you can also put a couple from the opposite side.
 
#33
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Yea that is a fix, but if he doesnt have the money to ship it to McM, then he wont have the money to buy aftermarket hardware. My point was, McM might replace the hardware for free and maybe even the shipping.
 
#34
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Dave, yes that would be the best fix IMHO, but Im not going to spend $125 on something that should work in the first place.
 
#35
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMCj</div><div class="ubbcode-body">Dave, yes that would be the best fix IMHO, but Im not going to spend $125 on something that should work in the first place. </div></div>

+1
 
#36
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Those screws always come loose, not the best idea - that's why the added the thumb wheel.

Read my post above, easy cheap fix and don't have to worry about it again.
 
#37
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Pat, thats a good idea if you are not going to be adjusting the cheek piece up and down to remove the bolt, in my case, I have to lower it all the way to remove the bolt, so it would be a big hassel each time to remove all the screws with a allen wrench. The whole point is to do it without tools.

I think I found an easy solution, Ill update the 1st post with pictures in a minute.
 
#39
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

In theory, it should fix the problem, but I havent tested it out yet. If you think about it, steel pointed thumb screw on aluminum posts is not something I would have expected from McMillan. No reason at all to point the thumb screws.
 
#40
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Guys I just wanted to make a correction, Ryan at McMillan offered to send me a UPS label and have the stock shipped on their dime for repair, I missed that part of his pm and wanted to clear that up.

But with the tips ground flat, I really think the problem is fixed. Will know for sure when I send some rounds down range.
 
#44
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

My A5 has the non thumb wheel cheek piece, I simply made a spacer and installed in under the cheek piece, the thumb screws still come loose but the spacer keeps everything in place.
 
#45
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Nhassey</div><div class="ubbcode-body">I told you man, McM has great customer service! They will take care of you. They are not in the business of scamming people uno? </div></div>


I dont think I ever said they were trying to scam me. I just wanted a quick fix instead of shipping them the stock. I am more than capable with tools to fix something as minor as this. And I have experianced their customer service first hand in the past, no question about them being first rate.


Cobra, this mod to the thumb screws should help them stay in place. You know, this wouldnt be an issue if the posts on the cheek piece were steel, like on the AICS. I had the same pointed thumb screws on my AICS stock and it never came loose while shooting. Not a good part for aluminum I guess.
 
#47
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Got a reply from Dick Davis, I've removed the chaff so you get the gist:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Your title to this e-mail says the thumbwheel cheekpiece, but <span style="font-weight: bold">the new elevator system is to replace the standard post and pillar type.</span> </div></div>


Now that I see the update above, I'll hit the belt sander and do the same to mine and report back after I get a chance to hit the range (probably about a week from now).
 
#48
Re: MCM A5 stock w/Thumb wheel cheek piece problem.

Ryan told me the same thing. Hope this mod works, or els we are pretty much out of options, unless someone makes the posts out of steel.
 
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