Re: Vertical stringing---Causes?
I think what is ment by "bag is under the barrel shank" is that the front bag is under the stock in the location of the barrel shank, just ahead of the receiver. May be wrong but that is what I took from it.
What is the rifle chambered in?
Does it always string vertical?
Does it start printing shots low and then go up or do they start high and walk down or is it random, just in a vertical line?
Has the rifle been accurized?
Is the barrel free floated?
Is this a quality barrel?
Is the receiver bedded to the stock?
There are so many things that can cause vertical stringing its hard to pick just one and say thats the reason without looking the rifle over.
In my experience, the single best way to get vertical stringing with a conventional opposing bolt lug receiver like most of the modern factory receivers is to have one bolt lug contacting the receiver but the other partially or totally floating.
With very low pressure loads generally accuracy is quite good all else checking out that is. As pressures increase you will see vertical stringing become much more appearant. This is a good reason to have the receiver totally accurized and then lap the bolt lugs into 100% SQUARE contact.
Also, if the barrel channel of the stock is touching the barrel, as the barrel heats up you will often notice your groups walking on you. The direction the shots walk are determined by where the barrel is contacted.
I would say 95% of the time, this is caused by something mechanical with the rifle. Poor machining, poor bedding, contact with the barrel. Very seldom have I found that adding pressure to a load will cure this problem. Generally it willmake it worse.
When adding powder to a load improves accuracy, this is generally because the bullets are not hit in the rear with enough pressure to cause them to bump up and seal the bore consistantly from shot to shot. This can be seen most often in factory rifles which are not held to much of anything as far as bore specs are concerned.
First place I would look would be your bolt lugs, then to see if the barrel is on contact with the stock anywhere.
Answer the above questions and it will help us point you in a more definate direction to what may be causing this.
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