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Old Yesterday, 09:50 AM   #1
Hog head
Join Date: March 26, 2009
Location: east TN.
Posts: 55
Bullet string

I'm in the process of finding the best load with my parts on hand and noticed a pattern of some vertical and some horizontal strings in my groups. What is this? Is it operator error or a function of velocity and bullet choice? At first I thought mabey I shot my groups too fast and it was barrel warpage then it changed directions. What gives? I don't think just dumb luck. It doesn't happen a lot just enough that I noticed it. Any thoughts?
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Old Yesterday, 10:50 AM   #2
Bart B.
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Join Date: February 15, 2009
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Most of it is caused by the shooter. Us humans are typically not as repeatable as our rifles and ammo are. Nobody holding onto a rifle pulled into their shoulder will shoot bullets as precisely than the rifle clamped in a free recoiling accuracy cradle or machine rest. We don't hold them exactly the same from shot to shot. Of course, this assumes reasonable care in assembling hand loads as well as decent rifle parts fit.

If the barrel warps as it heats up, shots tend to string in the same direction each time.

What cartridge are you shooting at what range?

A .308 Win with a 100 fps spread in muzzle velocity will string bullets vertically about 2/10ths inch at 100 yards due to that much spread in bullet drop.
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Last edited by Bart B.; Yesterday at 12:46 PM.
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Old Yesterday, 11:22 AM   #3
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Join Date: February 6, 2014
Posts: 408
Sometimes it is shooter induced, and i may be caused by something seemingly inconsequential. For example, i have to quailfy with 3 weapons evey 6 months for work. I am pretty consistant about it, but last year, thinking nothing of it, i had several cups of coffee in the hours leading up to my range time. As a result, i was all over the paper.... still qualified, mind you, but obviously looser groups... all because the coffee made me a little jittery. I hadnt even noticed until i shot. Lack of sleep or foood can have an effect too.

Anyway... if you were getti g both verrical and horizonal strings, itd put it down to the shooter.... if it were consistently one of the other, maybe not.... but switching between the two suggest that neither is a hardware issue. Next time you shoot, try to be mindful of any shifts in body position or muscle tension... if something you arw doing is making a muscle tired it may give you stringing in one direction... then you shift a little, and the axist of movement changes, shifting the stringing.
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Old Yesterday, 12:38 PM   #4
Join Date: March 4, 2005
Location: Ohio
Posts: 10,879
Hog Head,

If you have a slender barrel, they can whip pretty significantly at times. Heating the barrel until it start making or increases firmness of contact of the barrel with the stock can cause a shift like that.

You didn't say what you were shooting at what range or in what wind conditions.

In general:

If your gun needs re-bedding to float the barrel, re-crowning, bolt lug lapping or receiver face truing, there's a limit to what you can tune ammo to.

If the gun is good to go, you can prove that to yourself by purchasing some commercial match ammo, assuming it is available for your chambering. Usually it's pretty darn good and makes a good way to tell if your loads or you and the gun are to blame.

Make sure your primers are solidly seated below flush with the case heads, at least two or three thousandths past the point where you feel the primer anvil's feet touch the bottom of the primer pocket. Any lesser depth can lead to ignition delays that are too short for most shooters to detect, but which act like slow lock time and cause velocity and barrel time variation.

If none of those things are issues, try shooting an OCW round robin or an Audette ladder if you have the range. See if you can't trace that muzzle vibration.
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