Stock Repair - KMW Sentinel Crack

[FeMan]

I went out to confirm zero before a match and found my rifle was not grouping like normal. On the drive home, I wondered if something was loose. When I checked the front action screw, it was loose and took about a turn and a half to snug up nicely. Unfortunately, the front action screw then interfered with the bolt lug. I pulled the action out and found the crack pictured below. The stock has pillars installed.

I emailed Terry to see if this can be warrantied and am waiting for his response. If it isnt under warranty, I am wondering how repairable it is. To try and fix this, I was thinking about dremeling out the crack (which I am guessing goes around the pillar and all the way to the lug recess) and filling with Marine Tex. Do you think that will be adequate to hold? Are there better options? I milled and installed M-lock rails for weights and an Arca rail so I am hoping this is salvageable. Any thoughts would be appreciated. Thanks!

ks!

 

[Preacher]

Shouldn't be a problem doing that....

 

[pdhntr]

I went out to confirm zero before a match and found my rifle was not grouping like normal. On the drive home, I wondered if something was loose. When I checked the front action screw, it was loose and took about a turn and a half to snug up nicely. Unfortunately, the front action screw then interfered with the bolt lug. I pulled the action out and found the crack pictured below. The stock has pillars installed.

I emailed Terry to see if this can be warrantied and am waiting for his response. If it isnt under warranty, I am wondering how repairable it is. To try and fix this, I was thinking about dremeling out the crack (which I am guessing goes around the pillar and all the way to the lug recess) and filling with Marine Tex. Do you think that will be adequate to hold? Are there better options? I milled and installed M-lock rails for weights and an Arca rail so I am hoping this is salvageable. Any thoughts would be appreciated. Thanks!

View attachment 1278074ks!

If that particular pillar was the correct length, you shouldn't have been able to tighten it after the crack appeared.

By the looks of the crack, the pillar was not long enough and the stock let go. I would check this before doing any repair.

Jim

 

[Alex Wheeler]

Every time I have seen a crack in that spot on a stock it was due to there not being proper clearance inside the pillar for the screw. The pillar ends up acting as a recoil lug and the thin stock material behind the pillar cracks. Looking at the action screw hole on your stock I can see threads in the epoxy, which means the screw does not have clearance in that pillar hole. They may warranty that, but its gunsmith error not manufacturer error. Good news is its a simple fix. Remove the pillar and stock material behind it. Build up that area with epoxy. I would make up a mixture of 2 part epoxy (I use west systems) mixed with a filler like milled fiberglass for strength. But you could just use something like JB or devcon. Then drill your pillar hole and re bed the rifle.

 

[FeMan]

Thanks for the great information! I love this site!! I will remove it all, build it up, and re-install as suggested.

 

[joshb]

I agree with Alex and pdhntr. When I do pillars, they touch the action AND the bottom metal sits on the bottom of the pillar. Torquing the action screws puts a very little pressure on the stock. Add a thin layer of bedding gives about 1/32” or so between the top of the pillar and the action. The pillars are centered around the action screws with 1/16” clearance around the screw.

 

[muleystalker]

I agree with Alex also but I would add that there is something else going on also. I would say your pillar is not long enough also. If it was long enough no mater how bad the stock cracked as long as the pillar is in place you shouldn't be able to tighten the action screw enough to interfere with the bolt lug, unless from the being your screw was borderline too long and over the years of torquing the action screw the aluminum pillar compressed/deformed just enough to hit the bolt lug. But I would bet the pillar wasn't long enough and and when the stock failed the short pillar reared its ugly head.

 

[FeMan]

I drilled out the old pillar and used a Dremel to hog out the crack and surrounding area. There was a large area of air-entrained material in the area where the crack was about the size of my thumb nail. This, combined with a pillar that was too short were the issues.

 

[joshb]

Assuming a lot, your front pillar should be about 7/8” long from my memory.

 

[muleystalker]

Just for future reference when bedding a stock with pillars, after the bedding is done you should be able to she a portion of the metal from the top of the pillar showing through the bedding material.This is where the action was seated against the pillars while bedding. If you do not see the portion of the pillar top wear it was bearing against the action then it wasn't seated enough while bedding and the action isn't bedded on the pillars properly. Eventually you can have problems such as you did. Here is an example of the portion of the pillar showing where it was bearing on the action while being bedded. In your photo it looks like there was bedding material in between the action and the pillar, the pillar was never mated to the action.
It looks like your on the right track now. Post some photos of the finished fix.

 

[Alex Wheeler]

That would be a matter of opinion. I never let the pillar touch the action. I purposely cover the top of the pillar with the same thickness of epoxy as the rest of the bedding to get an even thickness and even shrinkage. I guarantee you will never have a problem like this because the pillar was not touching the action.

 

[FeMan]

I have heard both and have always pre-bedded pillars and then floated everything with a skim coat. I cant afford that kind of testing to prove either way to myself though! lol. This rifle shot under 0.2 before the mishap so I am hoping it is that good after my "fix". That will have to wait until after my meat shopping excursion though......

 

[AlNyhus]

In the pic, you can clearly see thread marks from the action screw in the pillar I.D. That's the kind of stuff that breaks stocks and causes accuracy issues. For standard 1/4-28 action screws, I make the pillar I.D. 5/16" and center the screws exactly in the middle.

As far as the action setting on the pillar tops...it's commonly done but it's not the best way to do it. Why would we want the action sitting on dissimilar materials (bedding and alum pillars)?

Good shootin'. -Al