Magpul Pro 700 Chassis problem, Need Help

[radonkun]

I got a Magpul Pro 700 chassis for my bighorn TL3
Everything is good at the start.
But when I shoot around 100 round, I figure out the Action Screw is loosening.
I make sure I tight to 60 in lbs. And continue to shoot another 100 round.
Yes... It is loosening again.
(I use the torque wrench set as 40in lbs can remove the screw, so I am sure the screw is loosened)
I bought two new screws and fit in.
It is loosening again after 100+ shot.
So I use some blue thread lock. (Red is too much power)
This time is better but not takes long.
It is loosening again.
I cannot find a lock washer to fit in, btw.

So, is there any good solution? Please do not use red thread lock, if I want to remove it someday.

 

[Snuby642]

Did you clean the threads good before using the thread lock?

 

[radonkun]

Did you clean the threads good before using the thread lock?

New screw, actually.
The action screw is easy to get in a hardware store, but get a longer screw and cut a bit will perfectly fit for TL3

 

[XLR308]

A high collar lock washer is designed to fit on socket head cap screws that are recessed but I wouldn't recommend that.
You need to find what is causing the issue instead of a way to hide it.
Remove the barreled action and look for contact marks in the inlet that something is making contact were it shouldn't such as a high spot.

 

[Snuby642]

New screws have preservatives on them normally.
Dissasemble clean both, with brake cleaner, rubbing alcohol at the least.
Dry thoroughly and try again.

 

[radonkun]

A high collar lock washer is designed to fit on socket head cap screws that are recessed but I wouldn't recommend that.
You need to find what is causing the issue instead of a way to hide it.
Remove the barreled action and look for contact marks in the inlet that something is making contact were it shouldn't such as a high spot.

I tried lots of time, remove it and put it on again. and try to find the problem. But it still loosen

 

[radonkun]

The video is here, and I shake the barrel, the screw is loosening.

 

[XLR308]

I tried lots of time, remove it and put it on again. and try to find the problem. But it still loosen

I think you misunderstood, I'm not saying just put it back in and expect a different outcome.
If you remove the barreled action and look over the action bedding area of the chassis if there is a high spot there will be evidence of it as a shinny spot or plastic wear from the aluminum being displaced since a small area is taking most of the load instead of it being evenly distributed.

 

[Snuby642]

May need longer screws?
The tl3 is not standard ?

This from bighorn's site:
Available tang options are trim, medium and thick. Trim is the closest to standard Remington 700 actions while medium is the same footprint just slightly thicker at the rear. Thick tangs typically require some custom inletting in stocks but can be more aesthetically pleasing in some chassis. If you have any concerns with which tang will work, follow the general rule that trim is the most versatile option.

 

[ZEROGUY]

I'm thinking something is tweaked between the action and chassis and there is uneven distribution of mechanical stress between the action and chassis bedding. I think XLR 308 may be onto something.

Study the contact area on the chassis and receiver and see if there any uneven patterning. Maybe even take a known good straight edge to the surface of the action and bedding area to make sure everything is true.

If nothing looks wrong I would try some different or longer action screws and trim to size, making sure you have at least 3 full rotations of thread engagement.

Make sure to torque them sequentially and incrementally, also when you reach your final torque value, make sure to torque both screws 2x. Blue loctite and thorough cleaning of receiver and screws are a must IMO.

Another option to look at if your problem persists is the nordlock washers, I think MPA is now including these with their chassis systems now FWIW. I thought about using some on my magpul chassis but my screws are holding just fine. I also haven't checked to see if they make one small enough in diameter that will fit in the action screw holes in the bottom of the magpul chassis, but either way they will require longer action screws to work.

 

[ZEROGUY]

Should note I am running a bighorn Origin with my chassis. No loosening issues to speak of.

 

[radonkun]

May need longer screws?
The tl3 is not standard ?

This from bighorn's site:
Available tang options are trim, medium and thick. Trim is the closest to standard Remington 700 actions while medium is the same footprint just slightly thicker at the rear. Thick tangs typically require some custom inletting in stocks but can be more aesthetically pleasing in some chassis. If you have any concerns with which tang will work, follow the general rule that trim is the most versatile option.

I already cut a perfect screw for TL3

 

[radonkun]

My action screw is perfect cut to fit. And the hole is too small to put a lock washer in.
I double checked, everything is okay but the screw is loosening. With blue thread lock, it will better than without.

 

[XLR308]

Glad you got it sorted out ?

 

[radonkun]

Glad you got it sorted out ?

This problem makes me headache every day, lol

 

[Tx_Aggie]

Have you contacted Magpul about the issue? That would probably be my first step.

 

[radonkun]

Have you contacted Magpul about the issue? That would probably be my first step.

Not really, cuz the super long waiting time on the phone

 

[radonkun]

I check Magpul video again and again.
I figure out, before tight the action screw, we should push the chassis recoil lug to touch the back of chassis hole. (It is hard to describe, so check the picture below)
I am not sure this is the problem or not.
So I removed the barrel action, cleaned the thread lock, and half tight the action screw. And I figure out there are around 1mm to 1.5mm space in the red arrow area. So I push the chassis all the way touch with recoil lug and mount as 70in lbs.
I reinstall the barrel action like the way.
Hope it goes well, I will go to the range recently to check the result.


More disscussion：Because English is not my mother language, I am trying my best to describe it clearly. I am not sure if I make a mistake that the recoil lug did not touch with the chassis. After I fired a few round the action recoil lug should go back to touch the chassis and stop. I am not sure now........


Magpul video:

From 4:40 in the video


Overall, Thanks to all people helped me, you guys amazing.

 

[Snuby642]

My recoil lug does not touch the action in 2 of the magpulls.
Both are 300blk so not any recoil with subs.
Have been lazy and not bedded behind the lug.
It is trying to center itself in the action, dont shove it back to touch.

I dont think all recoil lugs are the same and you will have to bed behind it.
Get some clay down in there and assemble it, when you pull it out you can see whats up.

I think the magpull vidio is wierd on that?
That void behind the lug needs filled.

 

[radonkun]

My recoil lug does not touch the action in 2 of the magpulls.
Both are 300blk so not any recoil with subs.
Have been lazy and not bedded behind the lug.
It is trying to center itself in the action, dont shove it back to touch.

I am using bighorn TL3 action, so the recoil lug and action is one piece.
Generally, I just drop and tight.
But the video told me a different way, I think I should try. Because I tried lots of ways to improve it. I owned this chassis for 3 months now.
I do not want to change another chassis for now, but if I cannot solve this problem. I think I will jump to Foundation or MPA ( I already have a Manner stock and wait for barrel action done)

 

[Snuby642]

All the stocks will have a void there to be filled I think you will find.
I have gotten away with it due to no recoil to speek of in the round used.
I put mine togeather to test it and have not bothered since.
I may change actions and will bed then.

 

[radonkun]

All the stocks will have a void there to be filled I think you will find.
I have gotten away with it due to no recoil to speek of in the round used.
I put mine togeather to test it and have not bothered since.
I may change actions and will bed then.

I think so, bed the action in the stock is the best way to do.
But people use DBM, because it is convenient. Just drop in and ready to go.

 

[XLR308]

I think so, bed the action in the stock is the best way to do.
But people use DBM, because it is convenient. Just drop in and ready to go.[/QUOTE

You can measure your action from the backside of the lug to the center of your front action screw hole and then do the same on your chassis from the lug pocket to center line of front action screw hole with a set of calipers. That will give you a good idea of the amount of gap present between the lug mating surfaces.]

 

[radonkun]

When I put the barrel action on the chassis and I put the rifle vertically. I tight half way of the action screw. The action can go front and rear maybe 1mm or bit more. Rear side will be stopped by recoil lug touch the chassis hole. So maybe try some recoil lug bedding???