Range Report Vertical Stringing - Help me to understand?

[Leaddog]

First time out the other day with my new rifle build. It's a 28" 10 twist .308 shooting Berger 185 LRBT. I was shooting at 300 yards over a chrono from the bench once I established a 100 yard zero.

I shot 5 rounds of 5 different loadings increasing in charge weight by .3 grains. Two loads grouped very nicely at one inch or less. The 3 other groups had a very apparent vertical stringing of about an inch and a half with all holes touching or very close.

What is this telling me? What causes the vertical in different loadings?

ES in the teens, SD in the single digits. New Lapua brass.

 

[jsm.usmc]

Re: Vertical Stringing - Help me to understand?

If you check out this thread Post1713419. It in depth explains everything about performing a ladder test. He explains why your impacts will string vertically. Also how to know which load to pick. Good luck

 

[bohem]

Re: Vertical Stringing - Help me to understand?

Bump up the powder charge to help tighten up vertical stringing.

Horizontal stringing is (when the shooter doesn't cause it) from either a touch too much charge or a seating depth issue.

 

[Bearwalk]

Re: Vertical Stringing - Help me to understand?

To elaborate a bit more on your question of why different loads experience different levels of vertical stringing...

The barrel vibrates as the bullet travels down it. The speed of travel is determined by your load, projectile weight etc. What matters is where the muzzle is in its vertical travels when the bullet releases. If the muzzle is at or near its maximum displacement when the projectile releases, the shooter will experience more vertical stringing than if the projectile releases when the muzzle displacement is near zero.

To picture what is going on, think of cracking a garden hose like you would a whip. Now place a marble in the hose and crack it. If you are able to time the release of the marble when the hose opening is at the horizontal, you can actually control where the marble goes more precisely than if the marble releases when the nozzle is pointed up or down.

All of this is referred to the "Optimum Barrel Time" concept. (Just google on it.) The are calculators out there that will help you find your "nodes" of minimum travel. If you use this in conjunction with the barrel travel time provided by Quickload, you can find your most accurate load in a fraction of the time it will take you in experimenting at the range.

 

[Leaddog]

Re: Vertical Stringing - Help me to understand?

I've worked with OBT and the accuracy nodes are either too fast (hot load) or much too slow (velocity) in my .308.

 

[bigwheeler]

Re: Vertical Stringing - Help me to understand?

Pic the powder charge between the best three groups and go with it. Bergers
are sensitive to seating depth so you should be able to squeeze a bit more out
of them by playing with it. You are looking for a charge that is the most consistent
with some forgiveness. Your best grouping load is not always the best pic if it is
really touchy. And barrels vibrate in all directions, it's not an up and down thing.
Your best accuracy comes when the shock wave is back at the chamber, not at the
barrel end. That is what determines a node.

 

[Bearwalk]

Re: Vertical Stringing - Help me to understand?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Leaddog</div><div class="ubbcode-body">I've worked with OBT and the accuracy nodes are either too fast (hot load) or much too slow (velocity) in my .308. </div></div>

What barrel length are you running? 22" is a good barrel length for 308 as you can hit a node at about 2450-2470 fps with a 180g Sierra.

 

[rcamuglia]

Re: Vertical Stringing - Help me to understand?


This will help you to understand:

http://www.varmintal.com/aeste.htm#600yards