Action Bedding and Stress

[Phil3]

I see considerable attention paid to having a "stress free" action and how important that is to accuracy. "Stress-free" meaning that the action is not forced into a new dimensional state due to the action screws being tightened. If the action bedding surface is not a perfect reverse mirror image of the action and recoil lug, then the tightening may bend, twist, or otherwise distort the action. Thinking about it, I am asking, "so what"? The answer I most often here is that it negatively affects accuracy or at worst, binds the bolt. Never had the latter happen, so am asking "how", (negatively affects accuracy) because when the round is fired, the cartridge is in the barrel, not the action. Sure, the back of the cartridge sits against the bolt face, but could a stressed action actually change that relationship enough to affect accuracy?

I am not saying bedding will not improve accuracy. Perhaps it does, but if so, I would like an explanation as to how a stress-free action contributes to that. Perhaps by limiting movement in the stock upon firing, despite the action being hard against the recoil lug and action screws tight? Or...?

I use Howa actions and if there is any action that would be stressed when not bedded, it would be this one. Why? Because the front recoil lug (integral w/action), has a threaded hole in the bottom for the front action screw. Typically, there is some open space under that lug, meaning that when that front action screw is tightened, it is trying to pull the front of the action down while simultaneously levering the rear tang UP. There is a definite bending moment on the action, but they seem to shoot just fine, bedded or not. See link below to see a pic of the action.

https://i0.wp.com/rifleshooter.com/wp-content/uploads/2017/05/Howa-1500-barreled-action-review-bottoms.jpg?ssl=1

Howa action at top, Remington below.

Just my curiosity asking questions.

[LynnJr]

Phil
Take your best shooting rifle to the range and shoot 2-3 groups with it as your baseline.
Take the action screws out and put two business cards under the tang and tighten everything back down.
Shoot 2-3 more groups so you can compare them to your baseline groups.
A proper stress free bedding job eliminates fliers and big groups.
I don't know if it's harmonics or voodoo but bedding is your friend.

[fish45]

The necessity of bedding is dependent upon the purpose of the gun and the goal you're trying to achieve. If your gun is already shooting as straight as you want then you don't have to bed it. Most people that get their rifles bedded do so because thats what everyone says is needed to achieve the highest accuracy potential possible from their rifle. Not every gun is going to "need" it.

While there are different methods that are used to bed rifles the two most common (in my opinion) are bedding to "free float" the barrel and pressure bedding (less common). Most people want the action bedded to achieve the best possible fit between their action and stock with space left between the barrel and stock so there is no touching between the barrel and stock. Touching of the barrel and stock is one of the common points of stress and the stock pushes on the barrel and is a cause of flyers, shifted points of impact, open groups, etc.

Some guys like to pressure bed their rifles. Typically by bedding the receiver and intentionally causing stress on the barrel by pushing on the barrel somewhere in the fore end of the stock. Using this type of bedding you control the pressure you put on the barrel. In theory this type of bedding is more accurate than free floating, but usually causes vertical stringing when firing multiple shots (barrel heats up and metal expands) so its more common on hunting guns.

If you're achieving the accuracy or goal you want you don't have to bed the rifle.

[Pardini]

The basic idea is to maximize the surface contact between the action and stock. This essentially makes the two parts one, in that the action cannot move within the stock due to the precise fit. This gives better to to shot consistency because the fit is always the same between the two parts. Some gunsmiths glue the action into the stock.

[ar15barrels]

I see considerable attention paid to having a "stress free" action and how important that is to accuracy. "Stress-free" meaning that the action is not forced into a new dimensional state due to the action screws being tightened. If the action bedding surface is not a perfect reverse mirror image of the action and recoil lug, then the tightening may bend, twist, or otherwise distort the action. Thinking about it, I am asking, "so what"? The answer I most often here is that it negatively affects accuracy or at worst, binds the bolt. Never had the latter happen, so am asking "how", (negatively affects accuracy) because when the round is fired, the cartridge is in the barrel, not the action. Sure, the back of the cartridge sits against the bolt face, but could a stressed action actually change that relationship enough to affect accuracy?

I am not saying bedding will not improve accuracy. Perhaps it does, but if so, I would like an explanation as to how a stress-free action contributes to that. Perhaps by limiting movement in the stock upon firing, despite the action being hard against the recoil lug and action screws tight? Or...?

I use Howa actions and if there is any action that would be stressed when not bedded, it would be this one. Why? Because the front recoil lug (integral w/action), has a threaded hole in the bottom for the front action screw. Typically, there is some open space under that lug, meaning that when that front action screw is tightened, it is trying to pull the front of the action down while simultaneously levering the rear tang UP.

Testing for stress in the action is quite easy.
Stand the rifle straight up with the recoil pad on the bench.
Mount a dial indicator on the barrel so that it measures to the bottom of the stock.
Now loosen and tighten the rear action screw and observe the indicator.
If the barrel is moving up and down in the stock while loosening/tightening the screw, the reciever is under stress.
Repeat with the front action screw.
Testing the screws independently shows you where you need to correct.
You might see a whole bunch more movement in one screw compared to the other.

A well bedded action will only show 1 to 3 thousandths of movement.
Many V block chassis systems will slow over 60 thousandths of barrel movement from the rear screw when the tang is not supported because the tang is being bent as the screw is tightened.

The reason that stress in the action effects accuracy is that the whole action/barrel vibrate during each shot.
The stress allows the reciever to end up in a different shape after each shot.
If the reciever is contorted differently each shot, the barrel can point to a different location for each shot.

A stress free reciever will return to the same shape after each shot and this causes the barrel to point to the same place.

[Phil3]

https://www.youtube.com/watch?v=_TwczrQoLek

https://www.youtube.com/watch?v=55CeFIpuxB8

https://www.youtube.com/watch?v=67fOgN8k49Q

[joefrank64k]

Testing for stress in the action is quite easy.
Stand the rifle straight up with the recoil pad on the bench.
Mount a dial indicator on the barrel so that it measures to the bottom of the stock.
Now loosen and tighten the rear action screw and observe the indicator.
If the barrel is moving up and down in the stock while loosening/tightening the screw, the reciever is under stress.
Repeat with the front action screw.
Testing the screws independently shows you where you need to correct.
You might see a whole bunch more movement in one screw compared to the other.

A well bedded action will only show 1 to 3 thousandths of movement.
Many V block chassis systems will slow over 60 thousandths of barrel movement from the rear screw when the tang is not supported because the tang is being bent as the screw is tightened.

The reason that stress in the action effects accuracy is that the whole action/barrel vibrate during each shot.
The stress allows the reciever to end up in a different shape after each shot.
If the reciever is contorted differently each shot, the barrel can point to a different location for each shot.

A stress free reciever will return to the same shape after each shot and this causes the barrel to point to the same place.

[ar15barrels]

If the action contorts differently after each shot (if under stress), this would only make a difference in accuracy if the attached barrel is pointing in a different place than the scope aiming point. But, since the scope is attached to the action, would not the scope follow any contortion of the action?

The action contorts under the scope.
The scope mounts move around on the receiver as this happens.
It's worst in open top recievers like a Mauser98, 1903 or any receiver that does not have a top bridge between the front and rear.
This includes a standard 700, model 70 or a Howa 1500 action.



The strongest actions have a closed top and bottom and will not contort as much.
This is your Bat actions as well as Surgeon or Defiance actions with the one piece scope base and recoil lug.

[sigstroker]

Or the new Savages, like the Stealth Evolution.

[ar15barrels]

Or the new Savages, like the Stealth Evolution.

Bolted-on scope bases don't really do anything for rigidity unless they are also pinned into place.

[LynnJr]

Phil
The picture shows the d
ifference between factory Remington 700's and the BAT action you shot at Sacramento on my heavygun.

[LynnJr]

Phil
The picture shows the d
ifference between factory Remington 700's and the BAT action you shot at Sacramento on my heavygun.

[Phil3]

Hi Lynn,

Yes, the BAT is not likely to distort much! As I recall, that gun was 65 lbs. and shot a 300 Weatherby Mag? Even it could not produce much recoil at all in a gun that massive!

Phil

[Ramsh00ter]

I've always felt controlling vibrations to be as important (if not more important) as worrying about stress.

When we put on a barrel tuner, our goal is to tune the barrel vibrations.

By having an action bedded correctly does not eliminate vibration, just lessons it while making more consistant.

JMHO
Randy

[LynnJr]

Ramshooter.
The picture is looking for the correct tuner weight in half ounce increments.

Phil
Your third video with the black and white stock looks like a Shurley Bros Hammerhead?