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Thread: Vertical stringing in lighter rifles?

  1. #1
    Boolit Master

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    Vertical stringing in lighter rifles?

    Are lighter rifles more prone to vertical stringing? If so, is it the front end lifting up under recoil? Or the perhaps buttstock flexing? Do you get better groups holding on to the forend, or letting rest on the front bag when shooting off the bench? Both rifles in question are my lightest and have synthetic stocks, Ruger American 358 and 77/357.

  2. #2
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    Winger Ed.'s Avatar
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    A few different things can cause it.
    Barrel heating & expanding possibly putting pressure between it and the front of the stock
    is a good place to start looking.

    Check out why bench rest shooters lean towards heavy, and free floated barrels.
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  3. #3
    Boolit Master
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    Stringing in a single direction can be the barrel heating. Some barrels move a lot under heat, some not at all.

    If it is only vertical then it could be powder temperature related (depending on how much stringing).

    And then, as above, it could be stock interference.

    To see if it is temp related then mark each shot on the target. Heating will consistently move the bullets in one direction (unless you let the barrel cool between shots, so try to be consistent).

    If the stringing is random, ie, #1 to the left, #2 to the right and #3 in the middle, then I'd vote for something mechanical going on.

    This does not consider things like inconsistent powder charges, differences in bullet weights, mixed headstamp brass, etc, etc. These can all cause elongated groups in the vertical axis.

  4. #4
    Boolit Master

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    Thanks. Both are free floated. The 77 had 6”+ diagonal stringing prior to free floating, but improved significantly after, with lighter loads and shot round groups around 3”. Heavier loads still string near vertically 6”. I tried slowing my shots down, but it didn’t seem to help. Brass is same headstamp, every load is weighed, boolits sorted. The American isn’t nearly as bad, but I’d like better if possible. I still need to do some more work, but just wanted to make sure it wasn’t my bench hold causing the problem.

  5. #5
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    Something else about thin barrels-- they 'whip' more so than a thicker one.

    Hold onto a thin rifle barrel and fire it.
    You can feel it flex and jump around as the bullet runs down through it.
    As it heats up, it does it more and slightly differently in relation to where the muzzle is when it turns loose of the bullet.

    This effect gets us back to why target barrels are thicker.
    They do it too, but with much less effect as to where the muzzle is when it releases a bullet.
    Also, with more mass, they don't heat up quite as fast-- which makes the effect worse and worse.
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  6. #6
    Boolit Master
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    Does the string start at one end and each bullet a little further away in the same direction?

  7. #7
    Boolit Master gc45's Avatar
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    Barrel heat does it! Shoot the same load and # of shots in a heavy barrel and compare.

  8. #8
    Boolit Buddy 414gates's Avatar
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    It's a combination of the barrel heating up and a pressure point somewhere.

    It causes successive shots to walk up the target in some direction.

    Seperate the stock, and inspect the area where there is barrel contact. Even if the rifle is free floated, it may be bedded under the chamber area, and somewhere there is a pressure point.

    I've corrected this problem for myself in a 308 Norma that was previously free floated by the stock maker, and I've seen the problem corrected in a 375 H&H that was action bedded, but not barrel bedded, and had a single pressure point under the barrel near the front stock screw.

    Mine was bedded under the chamber, the rest of the barrel was free floated. There was a shiny patch right at the edge of the bedding where the front of the chamber was contacting. I did a full length bedding job on it. Before, my shots would string north-east, with no grouping to speak of. My test after the bedding put 8 shots into one moa of 168 grain bergers, and another six into one moa of 155 Nosler.

    The 375 H&H I mentioned was also corrected by it's owner with a full length bedding job, including the action.

    There is a tendency for people to want free floated barrels because the benchrest guys have them. The benchrest guys also have very short, very rigid, custom single shot actions made from a steel billet, that doesn't flex under the weight of a free floated barrel.

    Unless the stock is defective, in that the wood was not properly cured, or finished, and it swells or otherwise changes dimension under different weather conditions, the barrel does not need floating. A synthetic stock doesn't need floating at all.

  9. #9
    Boolit Master
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    I want free floated barrels, even in synthetic stocks or chassis. It is not only bench rest folks. Most who shoot at longer ranges and want smaller groups lean toward free floated. I want my rifles to shoot to 1/2MOA or better with jacketed bullets.

    The problem with full length bedding is that wood does not change dimension the same as steel when it heats up. So, you get a different pressure on the barrel. The other aspect is it changes the dynamic response of the barrel to the bullet, ie, it damps vibrations. If it does this consistently every time you would be ok, but, most folks cannot count on that. If your rifle shoots the way you want, then don't change.

    There was a time when gun stocks were fitted to provide a bit of pressure at the tip of the forearm. This was when folks used long, thin barrels for hunting. Again, it does work for hunting rifles for most people, if done properly.

  10. #10
    Boolit Buddy 414gates's Avatar
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    I agree, everyone must do whatever they get the best results with.

    In most cases, a free floated barrel is bedded up to and including the chamber, there is still a part of the barrel in the bedding.

    If a thin barrel is free floated and strings in any direction upwards as it heats up, there is still a pressure point under the barrel, unless the chamber is also free floated, then you need to look for the problem elsewhere.

    There are a lot of variables to consider, this is the easier one to diagnose.

    Yes, the coefficient of expansion of wood / fiberglass / aluminium and steel differ.

    Expansion of the diameter of a tube the size of a rifle barrel is very close to zero at any ordinary operating temperature, and within the clearance of a bedding job, even taking into account the expansion of the stock material.

    The length of the barrel will change to a much greater degree than the diameter.

    Considering that the action is fixed to the stock, there is by default a stress differential at those contact points as well, which is so small it is always ignored.

    If your chamber is 1.5 inches in diameter, my limited math skills tell me that the expansion of circumference is about 0.8 x 10^-5 inches. Expansion of diameter is less. Hard to measure even.

  11. #11
    Boolit Master
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    The bench rifles we see at our indoor range are really free floated. If you could bend a silver dollar to fit, it would pass between the barrel and stock. Dollar bill floating isn't really free floated.

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    Boolit Master hoodat's Avatar
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    The older I get, my rifle philosophy tends more toward barrels that are at least a little heavier, stiffer, and usually shorter. Those long, skinny barrels are great for light weight hunting rifles that wring maximum velocity from the loudenboomer magnums, but the emphasis must be put on their accuracy as delivered in one or two shots from a cold barrel.

    My rifles that are used for high volume squirrel shooting, are capable of delivering TEN shots into 1MOA without much sweat. I wouldn't expect my skinny barreled elk rifle to do that. I am pretty happy if I can take my cold hunting gun, and deliver TWO shots into 1 MOA and on my point of aim. jd
    It seems that people who do almost nothing, often complain loudly when it's time to do it.

  13. #13
    Boolit Master

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    Quote Originally Posted by Norske View Post
    The bench rifles we see at our indoor range are really free floated. If you could bend a silver dollar to fit, it would pass between the barrel and stock. Dollar bill floating isn't really free floated.
    Good point. Slow motion footage really shows how much a barrel flexes. Both rifles could probably use a bit more clearance.

  14. #14
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    On a free floated barrel POI walking from heat is a product of barrel stress. In a stress free barrel you will get zero change of POI regardless how hot the barrel gets. Palma rifles tend to have longer barrels with 30" being common. Palma light barrel contours are common yet they have no walking issues. Heavy barrels with stress issues still walk.

    The issue is due to the high-volume manufacturing methods of factory barrels most are far from stress free.
    Last edited by M-Tecs; 02-26-2022 at 05:41 PM.
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  15. #15
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    Quote Originally Posted by M-Tecs View Post
    The issue is due to the high-volume manufacturing methods of factory barrels most are far from stress free.
    It was popular in the 90s or so, then sort of went away like moly coating everything.
    I remember cryo-treated barrels being offered at a slightly higher price than a regular one.
    It was said the super cold treatment de-stressed the barrel.
    I got a Shilean one back then in .30-06. It's great, but I don't know if it made a difference or not.

    I figure is is sort of like 'Martinizing' at the dry cleaners.
    You can pay for it, but don't really know if you got it or not.
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  16. #16
    Boolit Master
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    Yep, my barrels are free floated just under 1/8". And, no, the bedding does not touch the barrel at all. It stops at the recoil lug.

    I guess my question is, why not free float? Too easy to do. It removes all doubt that your stock might be interfering.

  17. #17
    Boolit Grand Master



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    Quote Originally Posted by Winger Ed. View Post
    It was popular in the 90s or so, then sort of went away like moly coating everything.
    I remember cryo-treated barrels being offered at a slightly higher price than a regular one.
    It was said the super cold treatment de-stressed the barrel.
    I got a Shilean one back then in .30-06. It's great, but I don't know if it made a difference or not.

    I figure is is sort of like 'Martinizing' at the dry cleaners.
    You can pay for it, but don't really know if you got it or not.
    Never said anything about cryo-treating.

    What I am stating is the high-volume production barrels are manufactured with methods that induce more stress that most of the methods used by custom makers. My point is that barrels walk due to heat affecting the stress. That is not directly related to barrel contour. Light Palma contour barrels shoot the same as heavy Palma contour barrels.

    Yes, light barrels heat up quicker so they tend to walk sooner if there is stress in them but your heavy barrel will still walk as it heats up if it has stress in it.

    Cryo-treat does improve machinability. Industry has been utilizing Cryo-treat for that for a long time. Most of my barrels are Cryo-treated simple because in I had to pay a lot price for items I machined that required Cryo-treatment. I could add the barrels to the lot so I got it done for free. It never hurt and it did see to improves some.
    Last edited by M-Tecs; 02-26-2022 at 11:13 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

    "Before you argue with someone, ask yourself, is that person even mentally mature enough to grasp the concept of different perspectives? Because if not, there’s absolutely no point."
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    - Wayne Dyer

  18. #18
    Boolit Grand Master
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    Are you shooting off a rest or bags? Vertical stringing can come from the gun jumping off the bags / rest at the discharge. Hold it like you would in the field and rest the hand, not the rifle, against the bag.

  19. #19
    Boolit Man
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    I think it mostly comes down to barrel quality. A really high quality light weight barrel will usually out shoot a cheap heavy barrel when you get it hot.
    I know savage straightens some of there barrels and that would put a ton of stress into the barrels, When a barrel starts to heat up those stresses ( from the manufacturing processes)start to show, resulting in point of impact shift.

  20. #20
    Boolit Buddy Ajohns's Avatar
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    Try a different primer. Vertical stringing can be primer batch.

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