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Thread: Vertical Stringing Question

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    Member wykee5's Avatar
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    Default Vertical Stringing Question

    I recently picked up a 7mm 08 barrel for my CVA Apex. The barrel is made by Bergara, and is supposed to be a quality barrel. I loaded up some rounds, and like a kid on the way out of the candy store about to take his first bite, set up to do some shooting. I took a shot at 50 to get on, adjusted the scope, and went out to 100. I was dead on left and right, but shot a vertical group of about 5". This continued as I worked my way up in powder charges. Even with varied charges, the gun is within an inch left and right, but I get about 5" vertical groups. The bullet is a 120 grain Barnes TTSX, new Norma Brass, and 42-44 grains of Varget.

    I was shooting off a bipod mounted to the sling stud on the stock, with the back end on a bag--essentially the same way I shoot in the field. There was some contact between the fore end and the barrel just in front of the front stock screw, which I removed. This did not seem to change results. I took one group off a lead sled for comparison, and that group was about 1.5" vertical, and within 1/2" left to right. I had another shooter take a group off the lead sled with the same load, which again resulted in a group that was about 5" vertical, and less than an inch left to right. I have taken about 25 rounds through the gun, and if I superimpose the targets from all the loads, I get an ellipse that is probably 8" high and only 1" wide at most.

    The gun is a single shot break action, and there is contact between the back of the barrel and the frame, which is OK. I assumed there should be, but some people say there should be a gap, and that you can take a few thousands off the back of the barrel, the lock-up will stay the same, and it will be OK as the round headspaces off the shoulder. I spoke with a tech at Bergara, and he said there should be contact between the barrel and the frame, so that should be OK. He said to check the contact with the stock, which I removed, and to make sure I was not resting on a hard surface, which I was not. I also tried a led sled which I mentioned earlier.


    What seems to be the issue here? The fact that the groups are very tight left to right leads me to believe I have a solvable problem with a barrel that may eventually shoot very well, but in the meantime, I am out of ideas. Any thoughts would be appreciated.

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    I suggest you try it without the Bipod.

    I doubt you will be using in in the field with the bipod.

    Smitty of the North
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    Quote Originally Posted by Smitty of the North View Post
    I suggest you try it without the Bipod.

    I doubt you will be using in in the field with the bipod.

    Smitty of the North
    I agree. I have a rifle that strings when I use a bipod. I now pillow it under the action when shooting from the bench, and it shoots fine. And this is with the barrel supposedly free floated. Lots of stuff happens when you fire a gun that you never see.

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    I make no claims to be any kind of expert,, but here is a target that demonstrates the effect of different bullet seating. All other variables were the same expect for seating.

    Just my experience, might be worth a try.

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    Member sayak's Avatar
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    I find this bullet seating dynamic to be fascinating and complex. I'm timid to mess with recommended COALs.

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    Quote Originally Posted by sayak View Post
    I find this bullet seating dynamic to be fascinating and complex. I'm timid to mess with recommended COALs.
    This is a good read and was the basis for me trying to find a "secondary accuracy node" because with my current rifle magazine limit did not allow me to get close to the lands. I have now used this method on 2 rifle and loads and both worked. I'm loading Accubonds, but the theory still applies.

    As already mentioned barrel stock pressure is the usual cause,,, but I have found seating to have an effect and it is cheap and easy to eliminate.

    Beware seating changes have an effect on pressures, so adjust powder charges accordingly.

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    Quote Originally Posted by sayak View Post
    I find this bullet seating dynamic to be fascinating and complex. I'm timid to mess with recommended COALs.
    I'm also timid to mess with COALs in load developement,

    BUT I never use recommended OALs except by accident. I just make sure the bullets are all seated to the same length, and not touching the lands. The reccommends are usually short, and will work, but they MAY create a a danger. I ran into that situation once. Rifle throats vary.

    I use .030 off the lands, mostly. I keep meaning to try deeper seating, but I usually do OK with .030 eventually. Maybe, I could do better, and I have one rifle, a Ruger, that is customized for my wife, that doesn't group worth a hoot.

    It's acceptable right now, with it's load, but I'm not comfortable with it.

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    Member wykee5's Avatar
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    Quote Originally Posted by Smitty of the North View Post
    I suggest you try it without the Bipod.

    I doubt you will be using in in the field with the bipod.

    Smitty of the North
    I actually take the majority of my big game animals (and varmints) shooting with a bipod. Even when I was in Alaska I took most of my animals off the bipod. I find the bipod much more available and stable than trying to find a branch, or shooting off of a pack. And I know I am not very good freehand, so I use the bipod when I can. The terrain and grass height of South Dakota lends itself well to the use of a bipod.

    But thinking that may have been the problem, I shot a group using a lead sled. My group shrunk to 1.5", but was still a vertical group. My Dad then shot a group off the sled, and his was about a 5" vertical group, the same as I was shooting off the bipod.


    Recommended COAL for the round is 2.800, but I don't hit the lands until 2.870. I started out seating my bullets to 2.820, which should put me 50 thousandths off, which is where Barnes recommends starting. After my results, I shot a group at 20 thousandths off and another at 100 thousandths off, all with the same vertical results. It seemed like no matter what I did, I shot vertical strings, which is where I ran out of ideas, and in theory eliminated some of the variables that could be causing it. Given that my group did shrink substantially when I went to the led sled, it leads me to believe it is a bedding or barrel seating problem, but given that the rifle is a single shot, and has a separate fore end, I am at a loss as to what to do about it.
    Last edited by wykee5; 11-14-2013 at 14:53. Reason: clarifying

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    Moderator stid2677's Avatar
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    Some rifles just don't like certain bullets, while they will clover leaf others.
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    so, assuming you may have checked it already...... make sure your action screws are tight. i figure that the side of the stock do well to keep the side to side movement down, or so, but if even a little play exists then the action could pivot up and down in the wrist area causing your flyers. also, do you have any way of testing without the scope to rule that out? again i'm thinking maybe something is just a little loose

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    Beware seating changes have an effect on pressures, so adjust powder charges accordingly.

    http://www.bergerbullets.com/getting...in-your-rifle/[/QUOTE]


    Does seating the bullet back farther increase or decrease pressure? I have never played that much with it.

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    Quote Originally Posted by swapdonkey View Post
    Beware seating changes have an effect on pressures, so adjust powder charges accordingly.

    http://www.bergerbullets.com/getting...in-your-rifle/

    Does seating the bullet back farther increase or decrease pressure? I have never played that much with it.[/QUOTE]

    I have read that seating deeper, increases pressures.

    Reference here

    http://bulletin.accurateshooter.com/...g-vld-bullets/
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    Some charts from the web.
    Attached Images Attached Images
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    Quote Originally Posted by swapdonkey View Post
    Does seating the bullet back farther increase or decrease pressure? I have never played that much with it.
    Answer is ether can increase true peak pressure but for different reasons. When you seat back you are reducing the volume of the case thereby increasing pressure. If you seat out near or on the lands yes you increased case volume so you’d normally think less pressure but now the short jump to the lands will likely increase your pressure.
     
    The larger the case and smaller the bullet caliber the less seating deeper matters because your talking a smaller percentage of the total case volume lost. And seating near the lands it matters little what the case or bullet are, it doesn’t get a running start at the lands so pressure goes up.
     
    Weatherby went max case volume, seated bullets long with very long jumps to the lands to keep pressure down and gain his extra velocity he was famous for. And they shoot well despite the common belief that best accuracy is attained with the bullet near the lands.
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    You didn't say how fast you are shooting your groups. Is the barrel warming up significantly during your firing of a group? Remove the forearm and rest the rifle on the action only and see if the verticle stringing doesn't stop. H&R break opens are good at stringing as they warm up. The cure for them is supposed to be to open the hole slightly around the fore arm screw and then installing an O ring under the head of the screw. I'm not familiar with your rifle so that may not work. What I think is happening is as the barrel heats it gets longer and relieves some pressure from the forearm to the action thus stringing vertically but not horizontally.

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    Quote Originally Posted by wykee5 View Post
    I actually take the majority of my big game animals (and varmints) shooting with a bipod. Even when I was in Alaska I took most of my animals off the bipod. I find the bipod much more available and stable than trying to find a branch, or shooting off of a pack. And I know I am not very good freehand, so I use the bipod when I can. The terrain and grass height of South Dakota lends itself well to the use of a bipod.

    But thinking that may have been the problem, I shot a group using a lead sled. My group shrunk to 1.5", but was still a vertical group. My Dad then shot a group off the sled, and his was about a 5" vertical group, the same as I was shooting off the bipod.
    I said that about the bipod, because in my limited hunting experience, The Buck Brush has always been too high for a bipod to work for me. At least, that's my perception.

    Even shooting sticks were more trouble than they were worth to pack around. I was unable to use them.

    I'm all for a steadier hold. A sitting position, is what has worked well for me.

    Back to the stringing, my guess is that there is something that interferes with the barrel when the bullet comes through. The bipod is suspect in my mind. Maybe it's something else. ???

    Thanks
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    I’m with rbuck, vertical string is usually from a trapped barrel heating and not able to move freely as it expands. Bullet, crown or load issues usually chuck them all over the place.
     
    Another possibility is sighting issues. I string vertical when using a peep, they just don’t work for me. If your running a scope the elevation adjustment could be bad and moving up and down or you could have a mounting issue that is effecting elevation only.
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    Quote Originally Posted by ADfields View Post
    Answer is ether can increase true peak pressure but for different reasons. When you seat back you are reducing the volume of the case thereby increasing pressure. If you seat out near or on the lands yes you increased case volume so you’d normally think less pressure but now the short jump to the lands will likely increase your pressure.
     
    The larger the case and smaller the bullet caliber the less seating deeper matters because your talking a smaller percentage of the total case volume lost. And seating near the lands it matters little what the case or bullet are, it doesn’t get a running start at the lands so pressure goes up.
     
    Weatherby went max case volume, seated bullets long with very long jumps to the lands to keep pressure down and gain his extra velocity he was famous for. And they shoot well despite the common belief that best accuracy is attained with the bullet near the lands.
    Dat's Goot, AD:

    Thanks.

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    Had the same problem with a T/C in 7mm. 5 shots in 5mins and it would string. Wait 5 mins between shots and it stay under 1 1/4"

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    Quote Originally Posted by rbuck351 View Post
    You didn't say how fast you are shooting your groups. Is the barrel warming up significantly during your firing of a group?
    The barrel is a medium contour, not quite full bull, but heavy and fluted. I had an ambient temperature of about 35 degrees, and was usually waiting a couple of minutes between shots. The barrel was not at all warm to the touch. My next step is going to be taking the stock off, and resting on some soft foam and see what that does. The fact that it is not throwing groups all over the place gives me hope, but I want to find a cure that is still conducive to shooting accurately and quickly in the field.

    The scope is a Leupold VX-III, and came off of a different gun, which did not have vertical stringing issues. So as much as I would like for it to be something simple with the vertical adjustment on the scope, I am doubtful that the scope is the culprit. I'll hopefully play around with it a bit here in the next week or two and post my positive results or my frustrations.

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