Action screw torque - interesting results

[Budget_Sniper]

Breaking in a new rifle can either be a lot of fun or a pain in the... I recently started the break-in and load development process on a new open rig. I put 50 rds through it in the first session, deciding on a seating depth with some promising groups. After the session, I noticed my front action screw had loosened from the original 50 in/lbs my 'Smith put on them to maybe 30ish. I replaced the front action screw and increased to 65in/lbs (my usual torque). Went back for the powder charge test and my groups went to poop. Scratching my head, and getting kinda pist, I decided to shoot a few groups at different screw torque. I guess I've always been pretty lucky that screw torque didn't make a big difference in my other rifles, but it apparently does in this one. Just thought I'd share, as this may not be something everyone checks if their groups aren't coming together. The four groups are torqued at 50/55/60/65.

This is a Defiance Deviant Elite in a Kestros ZR chambered in s SAUM wildcat @200yds.

 

[avidflyer]

Stock bedded?

 

[Budget_Sniper]

Stock bedded?

Yes, really nice bedding job using marine tex

 

[AlNyhus]

If changing screw torque changes group sizes, there's stress somewhere. -Al

 

[Greg Y]

.....or the screw is touching the bolt.

 

[AlNyhus]

.....or the screw is touching the bolt.

Could be that, too. Should be obvious.

 

[Budget_Sniper]

I tend to agree with you that there's something in the stock effecting harmonics, but I'm not seeing anything obvious and the screw length isn't a problem. I'll add that this is the first z-rail stock I've used, I could see that making a difference. All that said, I feel pretty good about the 60 in/lbs results. I'm curious if anyone has thoughts on the POI coming down for that group compared to the others?

 

[L.Sherm]

I think there's a video out there on how you can use a dial indicator to see if there's stress in your bedding.

 

[rijndael]

Before I drew conclusions from this test, I'd suggest running it a few times.

I know plenty of people who can produce a target like that when making no changes to their gun/equipment.

 

[AlNyhus]

Stand the gun up on the floor...butt on the floor. Holding the fore end of the stock at the end, lightly lay your index finger on the barrel. Now loosen the front action screw and see if you can feel or see and barrel movement when you do this.

Then snug the screw down and repeat the process with the rear action screw.

If you have or have access to a magnetic base dial indicator, you can use it like this...tip of the indicator on the stock.

Or use this slick little bedding checker.

 

[dusterdave173]

My Savage BVSS with bedded lug will print crazy good groups with stock screws at 21 in lbs--go up --groups open up--having it pro bedded as we speak while getting a new barrel
I have a remington varmint with plastic stock it acts very similar--loaned to a pal--he cleaned it took stock off--would not group well--in that case Tighten it way up and it went back to printing smiles and ragged holes
each one is different just have to get to know what they like I guess

 

[L.Sherm]

with bedded lug

This is why you full length bed 100% stress free, Al is 100% correct

 

[Steel Mover]

It may be bedded but is it pllar bedded and 100% contact bdded, action and bottom metal? That setup should be shooting the same, with snug screws, not changing group sizs and elevation. Yes I did noice the group center changed, lower at 60.

 

[boltfluter]

You have a bedding issue somewhere. Nice bedding checker Al!
Paul

 

[AlNyhus]

You have a bedding issue somewhere. Nice bedding checker Al!
Paul

It's made by a pretty crafty guy in Iowa that does all sorts of 3D printed items for shooting. Here's the link to it on ebay:

Rifle Action Bedding Checker | eBay

This version works on most barrels including 1.25" F-Class barrels. This is a new version that I think is easier to attach by reducing the number of screws and the ability to. The indicator is not included.

www.ebay.com

 

[Skedaddle Shooter]

It's made by a pretty crafty guy in Iowa that does all sorts of 3D printed items for shooting. Here's the link to it on ebay:

Rifle Action Bedding Checker | eBay

This version works on most barrels including 1.25" F-Class barrels. This is a new version that I think is easier to attach by reducing the number of screws and the ability to. The indicator is not included.

www.ebay.com

That’s slick, just bought one.

 

[rebs]

If changing screw torque changes group sizes, there's stress somewhere. -Al

how do you find where the stress is

 

[Homerange]

.....or the screw is touching the bolt.

I had IIRC a Rem 770 in 7mm08 that did that when you properly tightened the front action screw.
I'd recently acquired it and never seen an action that needed the front screw to be so loose for the bolt to cycle and when it printed an 1" wide group with barely any vertical it was plain to see someone had mucked with it and possibly refitted the wrong action screw.
Anyways, shortening the screw for it to be tightened properly and not bind the bolt had it shooting okay with factory loads and later I went in to develop a nice 120gr load punching small clover leafs at 100 < my primary requirement for a sporter.

 

[std7mag]

You are being redirected...

You should really read the tech articles sometime.

 

[AlNyhus]

how do you find where the stress is

Sometimes it's very apparent. Sometimes not. On a complete rifle that needs bedding, I strip the receiver of everything...trigger, mag box, etc. and start from there to determine where the issue(s) are. If the issues are the trigger, mag box or other metal stuff, that will be seen later. From there, it's a matter of taking your time and just looking as you take the barrelled receiver in and out. I normally check the recoil lug mortise first. If the gun has the front action screw that goes into the bottom of the recoil lug, that's the first suspect area. On the stocks with aluminum bedding blocks, you can get a good indication by the marks on the receiver where it makes contact with the bedding block. Action screws contacting the inside of the pillars or stock, 'secondary' recoil stops are all suspects.

Really though, it's kind of hard to describe the process. Just take your time and look at everything. Each action type has it's own quirk and there's no one size fits all solution.