Vertical stringing - some help diagnosing if you please

[hardlyworking]

What to do about vertical stringing?

This is a PT&G blueprinted action + PT&G bolt.
Remmage/barrel nut set up (I am not mentioning the manufacturer at this point intentionally)

Put into an XLR Element chassis (with the folding stock adapter, has some wobble)

Shooting 140 Berger Hybrids out of a 6.5CM Lapua case

.... At 25 yards, the grids are 1/4 inch so every grid square is 1 MOA

Now, I could absolutely suck, that is not out of the question. But what I saw, calling my shots was that over the course of 5 rounds in each group:
1st shot was touching/nearest the 4MOA black squares
2-5th the shots printed left about 1 MOA and then lower and lower over the course of the string

All shots are from a bipod (but no rear bag)

Is this recoil fatigue? Bucking/Anticipation? These all felt like good trigger presses, and I didn't call anything bad.

The three groups cover the same powder charge and only changes the primer either CCI #41, CCI 400, or Winchester Small Rifle (bottom right). I have since chrono'd the #41 and 400s and found the SD and ES of the #41s to be much higher than the 400s... but I don't think explains a 2-4 MOA shift over 5 rounds.

Would this happen with a heavy varmint barrel heating up? Or is it more likely to be shooter problems?

[Bete Noire]

Breathing?


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[longrange1]

its not the barrel heating up....you need to shoot the same loads with a rear bag to eliminate shooter error and then go from there...LOTS of things can cause stringing start with the simple things.

[pacrat]

its not the barrel heating up....you need to shoot the same loads with a rear bag to eliminate shooter error
and then go from there...LOTS of things can cause stringing start with the simple things.

Agree with underlined. And will add that "shoulder pressure" is every bit as important to minimize vertical stringing as any other variable.

JM2c

[LynnJr]

Horizontal stringing is the shooter.
Vertical stringing is the load.
Go up 0.3 on your powder charge and let us know what happened to your groups.

[longrange1]

[RNE228]

Agree with bags. Support the rifle. Simple and easy to do.

It's a good idea any time you're working up loads.

[russ69]

...I often see guys using bipods with hard, and often sharp, feet resting on these benches. Their guns "hop" like crazy when you introduce a little energy to this "hard on hard" arrangement....

As everyone has said, use sand bags front and rear. AND, it's a rifle, for all that is holy move it out to at least 100 yards, geeze.

[longrange1]

[sigstroker]

Or a Lead Sled? To eliminate the variables?

[longrange1]

[LynnJr]

Hey original poster I missed the no rear bag when I first responded.
What is holding up the rear of the rifle your hand? Something else?
Vertical stringing isn't a barrel issue so it doesn't matter who made the barrel.
Take the bipod off of the gun and put it on some bags that are the proper height for 100 yards.
If your forced to lift or put pressure on the gun to center up the crosshairs your wasting your time.
The bench in the picture is using 1-1/8 inch marine plywood. I had it 3 layers thick but it was too heavy so I replaced the top with a single sheet and my rifles quit shooting. I added a second sheet back but have yet to test it out. All of the pipes are welded and the entire bottom is a sheet of 1/8 inch steel plate. I can stand on the top.
You also mentioned now that I reread your original post that your using a chassis that folds and it wobbles.
If the bags don't cure your vertical your second source of error to look at is the wobble.
The reason the single sheet of plywood didn't work is the top is larger than most and it was too springy. With a heavygun(65 pounds) the top was acting like a trampoline between shots.
Your wobble in the folding joint can duplicate that problem.
My original post should have read that vertical stringing from a properly set up rifle is the load.

[ar15barrels]

All shots are from a bipod (but no rear bag)

Is this recoil fatigue? Bucking/Anticipation? These all felt like good trigger presses, and I didn't call anything bad.

If the parallax is set correctly, it's the lack of a rear support (shooter error).

[hardlyworking]

Thanks guys! Will get a rear bag.

In my case the rifle "only" weighs about 15 pounds and is meant to be at least somewhat man-portable.

I've obviously heard of sand-bags, but what I am seeing more and more these days are purpose built bags that are very light, filled with hollow plastic beads or somesuch. Are these recomended?

Or does your rear bag also have to have 5 pounds of sand in it to work for what we are talking about?

[longrange1]

Vertical stringing - some help diagnosing if you please



You can buy these empty for about $10 bucks or with beads just dump the beads and fill with sand....a solid bag is best.


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