Action "Stress" - Please Explain

Discussion in 'Main Message Board' started by Phil3, Dec 8, 2018.

  1. Phil3

    Phil3

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    I am wearing my flame suit for this post, but I am asking this question simply because I want to understand the "how" and "why" of things. Who better then people here to answer that on rifle accuracy.

    I have heard it is important not to "stress" the action when securing it in the stock. Proper torque and tightening sequence are often the order of the day. I am going to assume (correct me if I am wrong), that stress is meant to define any force applied to the action that causes it deviate from its relaxed dimensional state (i.e., sitting on the bench).

    Assuming my definition is correct, if the action is torqued down onto a surface that is not a perfect mating surface, or tightened in a way that places a strain on the action, then the action may be considered "stressed". I want to know HOW this affects anything. I am NOT saying it doesn't, just looking for an explanation on HOW it does. Bolt binding? Perhaps in a custom action with tight clearances. What else?

    Can an action be stressed with 65 inch lbs. of torque (5-1/2 lb. ft. lbs.) applied to the action screws and if so, what are the negative consequences?

    I wonder about the Howa shown below.

    [​IMG]

    The bedding surface is behind the integral recoil lug. The front action screw threads into the recoil lug. If there is even a slight gap between the bottom of the lug and the stock, then a bending moment is created when the screw is tightened, pulling the front of the action/barrel down, and/or the stock, up. Imagine tightening the front bolt first, a bit too much, levering up the rear, and then clamping down on the rear screw. Is anything really going to move, bend, to a meaningful degree, with 65 in. lbs. of torque? And if it does, what is the negative consequence, and why?

    I also wondered about action stress when a 5 - 8 lb barrel up to 30" long is hung off the front of the action.

    I wish to emphasize, I AM NOT STAKING OUT A POSITION. I am asking questions only, to better understand this aspect of rifles and to learn.

    Phil
     
    Last edited: Dec 8, 2018
  2. Shawnba67

    Shawnba67 Silver $$ Contributor

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    Heres an answer to part of your question. I bought the Greg Tannel action truing dvd and he states 40in lb is enough to bend an action in the truing fixture at least. I used a torque wrench to get a good feel for 40inlb. For me that was a thumb and 2 fingers on a wrench NO WRIST!!! I tried it on an action after i had reamed the raceway to .710 with the Manson tool. If i tightened much past that, the reamer shaft would bind in the bore. So yes I think in a perfect situation yes 50inlbs can bend an action.
    Does it matter? Thats well above my paygrade.
     
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  3. Bart B.

    Bart B.

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    Every action is stressed by the barrel weight putting more force at 6 o'clock on its tenon shoulder than at high noon.

    Firing a round makes the barrel tenon shoulder put forces at both 12 and 6 because barrels mostly whip vertically but a little side to side. Stiffer actions resist bending from this. Interesting to note that the Winchester 70 receivers are stiffer than Remington 700 ones in the vertical plane. Especially the Win 70 ones made for the US Army teams without magazine cutouts.

    Some additional stress comes from stock screw tightness.

    Yes, some more stress from tightening the barrel to the receiver. Extensive tests in the 1960's with Win 70 based match rifles showed 60 in-lb on all stock screws was best for accuracy.

    The US Navy built match Garands had about 30 to 35 pounds pull down force about mid point on the barrel at its lower band. The best ones tested a bit over 1/2 MOA at 600 with handloads.
     
    Last edited: Dec 8, 2018
  4. BoydAllen

    BoydAllen

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    In terms of accuracy, it is best if a barreled action does the same thing for each shot. If there is stress in the action, because of bad bedding it not repeat as well as it would if there was none, given that the stress is the product of an imperfect fit. You may notice that glue in bedding has taken over short range, group benchrest some time ago, and if you are paying attention you might notice that it is making inroads in long range as well. Of course an action has to be properly bedded before it is glued, but the glue, ties stock and action together better than action screws alone can, and makes a consistent job easier to produce. Another issue is the unit loading of contact surfaces. In the case of bad recoil lug bedding, it may be that by concentrating the force of recoil on one side or corner that the action moves more fore and aft, and the probability of it resetting to the same position is reduced, being dependent on whether the compressed material that is in contact with the lug, rebounds exactly the same each time. People tend to view steel as being rigid and while it is in a relative sense, it does move under load.
     
    Last edited: Dec 8, 2018
  5. Shoebox

    Shoebox

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    Great question
    Thanks for the explanation's
    This is why this is a great forum !!
     
  6. dgeesaman

    dgeesaman Gold $$ Contributor

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    I agree with your definition. In engineering design circles I might instead use the more specific word prestressed or a state of having internal stresses.

    Even small screws with light torque have significant clamping capacity. I'm sure it helps to keep the action in the original dimensional form as much as possible, but I believe the more significant benefit of a well-bedded action comes from more consistent vibration during the firing cycle. (Good luck measuring that to prove/disprove it). There is always vibration, and aside from the surfaces under the bolt heads, the stock and action will vibrate and deflect a bit independently. Bedding should help unify their vibratory response through the firing cycle.

    David
     
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  7. Bart B.

    Bart B.

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    Barrel vibration is very repeatable if the receiver stays in place in its epoxy bedding. But that can change.

    Best example of that was when Remington 700 actions were first used in NRA match rifles for the 308 Win cartridge in the 1960's. They twisted enough from barrel torque with heavy bullets to work loose in epoxy bedding. Accuracy suffered. Every few hundred rounds, rebedding fixed it. Half as many rounds of 30 caliber magnum's heavy bullets.

    2" long recoil lugs were tried and helped a little. Flat bottom and side sleeves worked best.

    Or use a Winchester 70 action that didn't need rebedded for the lives of 2 or 3 barrels.
     
    Last edited: Dec 9, 2018
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  8. Texas10

    Texas10 Gold $$ Contributor

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    There's no doubt in my mind that dampening vibrations related to the firing cycle are a big part of reason bedding and torquing actions into the stock, and for best accuracy, dampening in a consistent manner is key.

    With that in mind I wonder if any gunsmiths or gun makers have experimented with heat treated or hardened materials in action building, or another metal besides 4130 and it close relatives. Would a 4130 barrel screwed into (lets say) a titanium action be any better? Or heat treated A-2 tool steel or 4340?

    I used to build solid propellant rocket boosters with heat treated 4340, and that was some tough stuff!

    Or would a sharp change in metal hardness or toughness at the barrel/action junction create more problems controlling stress?

    Now, back to my coffee and fruit cake....:D
     
  9. Iowa Fox

    Iowa Fox

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    Coffee and fruit cake, your killing me.
     
  10. liljoe

    liljoe Silver $$ Contributor

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    I know that using different materials in the face of the action has been tried.
    Different grades of stainless and titanium.

    Joe
     
  11. kountryboy2

    kountryboy2 Gold $$ Contributor

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    I find that hard to believe .
     
  12. Bart B.

    Bart B.

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    Measure both and you may easily believe.

    70's weigh more and have more metal resisting vertical bending than 700's.
     
  13. kountryboy2

    kountryboy2 Gold $$ Contributor

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    I have .Harold Vaughn agrees with me. I love model 70s both pre and post 64 . Ed Matunas who worked at Winchester told me the same thing. Ed shot alot of benchrest in the late60s and early to mid 70s .Winchester built him a single shot model 70 in 222 it would never shoot with a gun built off of a 700 action.
     
  14. BoydAllen

    BoydAllen

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    Another issue was what bedding compound. I am told that Microbed would soften when it was warmed up, and much of this was pre pillar....I think.
     
  15. Bart B.

    Bart B.

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    In the book I read, Vaughn said Wins were near 3 times stiffer than Rems.
     
  16. kvd

    kvd Silver $$ Contributor

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    If this is indeed the case. What is it about Remington actions that make them and their clones to predominate in custom builds. One hardly ever hears of a Winchester action being used in a competition rifle (rimfire not included). Not being argumentative, just curious because I've sometimes wondered why this is so, and also Browning actions?
     
  17. Bart B.

    Bart B.

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    I'm not responsible for others lack of this information, but here's my opinions.....
    They were used to win more matches and set more records than Remington ones in the heyday of 308's in NRA match and long range rifles. One such rifle fired the smallest series of 10 shot groups at 600 ever produced.

    Probably because Winchester never sold their more expensive actions alone and zillions of aftermarket things for Remington ones were available. Plus the use of Remington actions in early benchrest rifles and their factory barrels were more accurate than Winchester ones.

    One other reason.... in the late1960's when the military wanted a new sniper rifle to replace the old Winchester 70's, top brass chose Remington; Winchester was in dire financial straits and not thought a good idea. In spite of all the snipers knowing Winchesters were more reliable and easier to maintain afield.
     
    Last edited: Dec 9, 2018
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  18. kvd

    kvd Silver $$ Contributor

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    I suppose too that the Remington clones such as Borden and others have features and extra material in their construction that more than make up for any deficiencies that a stock Remington action may have next to a factory Winchester action.

    Thanks for responding and for the information.
     
  19. jdh47

    jdh47 Silver $$ Contributor

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    Remington's main draw is it's easier to set up in a lathe than a flat bottomed action. They have been the most trued and barreled actions of all other makes. Most of all the customs are Remington clones. After market support is good for the Remington action.
    The M70 action is a fine one and it's fire control and ejection is very good. A good pre 64 action is, or can be made, very slick. M700 not so much.

    The M70 was pretty much a custom from the start and the M700 was designed for ease of manufacture. Savage has taken that to a higher level and Remington is now the whipping boy.
     
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  20. Toby Bradshaw

    Toby Bradshaw Gold $$ Contributor

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    In the benchrest game, the M70 is too heavy to make a good SP/LV.

    Action stiffness is probably overrated as a contributor to precision shooting, anyway. Look at the dual-port configurations that dominate in short-range benchrest, vs. the "extreme stiffness" attempts like the old shellholder boltface Wichita actions. Rate of fire beats resistance to bending.

    According to Vaughn it's the symmetry, not the number, of holes/cutouts in the action that is important for precision shooting.

    [​IMG]

    [​IMG]
     
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