Investigation: talley screws too soft or receiver 's problem?

[ssimo]

Hello everyone. I have just encountered an issue while mounting some Talley bases on my bergara b14 (rem 700 clone). Basically i installed the bases (talley 2 piece, aluminum) a couple months ago and the rifle was shooting very well. I didn't loctite the base screws down because i knew i could have had to swap the base screws in case i had some issues, so i just tightened them at 26 inch lbs (3 Nm), as Talley recommended me (they told me 25 inch lbs). Today i removed the bases to loctite them down and, while screwing off one of the 4 screws (the most forward one of the rear base), i noticed it was not clamping the threads (first time i screwed it on i didn't notice anything weird). When i removed the screw, there was some white grainy powder, like something coming from a chemical reaction, inside the threads and on the screw and the last part of the screw threads was stripped off, totally flattened. That's when i started doing dumb moves
I cleaned the threads, inspected them with my phone camera and a flashlight and they looked perfect. So i just tried to screw the base back in with another talley screw of the same kind (the rear one) just to see if it would have been stripped. After not much force, with my 200 euros torque wrench (recently rechecked for being accurate), I started screwing on the screw. After a few turns and not even too much force, it lost all its clamping force, I took it out, the last part of threads was stripped/flattened, again. The other screws in the other holes worked just fine and, after torqueing them at 26 inch lbs and then removing them, they look perfect. So the problem is happening only with that specific receiver hole and it happened with two different talley screws.
1) what the hell is going on with that single receiver hole? Visually its female threads look perfect
2) what was that white gritty stuff?
3) why the first time i installed the base i didn't have any issue? Everything must be related to that white stuff.

I attach a pic of rhe screw i removed from the base the first time I unisitalled it, with flattened threads and the white stuff on it. And pics of the receiver hole giving me issues from all 4 angles. Threads look fine to me.

 

[Wapiti1]

The receiver hole needs to be chased with a tap. I'd suspect they tapped that hole with a worn out tap and it's galling the screw into submission. The white stuff is the lower screw threads being packed into the threads above them.

You want a 6-48 tap. Not a typical size, so you will probably have to order one. Can be found on Amazon, Brownells, Midway USA.

Jeremy

 

[ssimo]

The receiver hole needs to be chased with a tap. I'd suspect they tapped that hole with a worn out tap and it's galling the screw into submission. The white stuff is the lower screw threads being packed into the threads above them.

You want a 6-48 tap. Not a typical size, so you will probably have to order one. Can be found on Amazon, Brownells, Midway USA.

Jeremy

So basically a manufacturing issue in your opinion?

 

[hereinaz]

Looks to me like a manufacturing defect. I agree about the cause. I am somewhat surprised that it is the screw threads giving up the ghost, with my luck it is always the hole that gets ruined. I'd say it needs to be chased with a tap because it is undersized. The tap should clean up any little damage to the threads and open it up to accept the screws. If you haven't used a tap before, its like twisting in a screw. But, as you turn it in deeper it will slowly cut the threads to the right size. As long as you don't "cross thread" the tap, you really can't mess it up. Just make sure you get the right sized tap, for all the dimensions including thread size.

If the screws aren't going in properly and they come out like that, then the screw or hole is messed up. You say the screws work in every other hole, so it must be that one hole. A worn tap is going to create a smaller hole with threads that are too tall and grooves that are too short. And, if they short stroked it, the hole could be tapered which is why it starts fine but the deeper the screw goes, the more it gets messed up. Because it is smaller, you are forcing a bigger peg into a smaller hole and the metal doesn't slide past, it grips and galls.

 

[ssimo]

Looks to me like a manufacturing defect. I agree about the cause. I am somewhat surprised that it is the screw threads giving up the ghost, with my luck it is always the hole that gets ruined. I'd say it needs to be chased with a tap because it is undersized. The tap should clean up any little damage to the threads and open it up to accept the screws. If you haven't used a tap before, its like twisting in a screw. But, as you turn it in deeper it will slowly cut the threads to the right size. As long as you don't "cross thread" the tap, you really can't mess it up. Just make sure you get the right sized tap, for all the dimensions including thread size.

If the screws aren't going in properly and they come out like that, then the screw or hole is messed up. You say the screws work in every other hole, so it must be that one hole. A worn tap is going to create a smaller hole with threads that are too tall and grooves that are too short. And, if they short stroked it, the hole could be tapered which is why it starts fine but the deeper the screw goes, the more it gets messed up. Because it is smaller, you are forcing a bigger peg into a smaller hole and the metal doesn't slide past, it grips and galls.

Thanks for the reply, now i understood better
Btw, why that got worse? In the first screw, threads flattened just a bit and i was still able to torque to specs, with the second and third one i tried, screws just became 100% flat in the last section

 

[hereinaz]

Can't say for sure, but probably some galling where you can't see it in the receiver threads after the first screw went in.

I presume that this is the first time you ran screws into the receiver?

 

[Wapiti1]

So basically a manufacturing issue in your opinion?

Yep. It would be super weird for you to have two bad screws.

Jeremy

 

[ssimo]

Can't say for sure, but probably some galling where you can't see it in the receiver threads after the first screw went in.

I presume that this is the first time you ran screws into the receiver?

Second time. The first time i was able to get to the desired torque but the screw got F up anyway, the threads are just a little bit less flattened on it.

Will this be fixed by a taper tap?

 

[FacePlant]

Will this be fixed by a taper tap?

If its a thru hole, not a blind one, it should work. Just remove your bolt first.