Virtical stringing

[Rookie]

7mm/08 Remington VSSF barreled by Pacnor with a extra heavy Sendero contour barrel 26" 1/10 twist, skim bedded into the Remington HS stock. Lapua 243 brass fire-formed to 7mm/08 chamber. Hornady 162 A-Max and Berger 168 Match bullets. H4350 and H4831 powder, 210GM primers.
I've tried 8 different combos and I'm getting vertical stringing with everything. Groups are 1/2 to 1 inch tall by less than 1/4 wide.
Any Ideas? I'm thinking primers?

 

[kentuckytroutbum]

Rookie-

Have you tried chronographing your loads? Check your SD & ES to see what that is telling you. Could be your powder, or primers, etc. Usually vertical stringing indicates varying velocities, or it could be that your barrel is not free floating, and as the barrel heats up, the stock is putting pressure on the barrel, and can cause stringing. Check to see if your barrel is doing that.

Bill

 

[bowslngr]

IMHO velocity variation does not produce vertical strining at 100 yds (I assume that is the distance you are shooting). Takes considerably more range for velocity differences to show up on paper. At 100 yards I tend to believe vertical stringing results from inconsistant recoil control and/or inconsistant pressure by your cheek and hands on the rifle.

 

[artbosco]

I've tried 8 different combos and I'm getting vertical stringing with everything. Groups are 1/2 to 1 inch tall by less than 1/4 wide.
Any Ideas? I'm thinking primers?

Stick with one combo: bullet, powder, primer, neck tension, seating depth. At least until you've wrung the heck out of it. Start with the most advertised best combo for your cartridge.

A barrel usually goes from in-tune to out-of-tune within a .6 [6/10th] of a grain range at or near the established best shooting nodes for your specific cartridge. For example, my 6PPC has two good nodes, one at around 29.0 to 29.2 grains of Vhitavuori N133, and another around 29.8 to 30.0. Somewhere within a .6 of a grain range at or near those nodes I find what the current barrel likes, and then once I do, I never change until I change barrels or change powder lots.

In addition, there's a host of variables that can induce vertical stringing. Here's a check list for evaluation: http://www.accurateshooter.com/shooting-skills/cures-for-vertical-stringing/

 

[Elkbane]

Rookie,
If you're getting vertical with that many different loads, I'd start looking at the things that were held constant across your range of loads. In your situation, I'd look at my cases first. Sounds suspiciously like doughnuts from necking up the 243 cases. I had a similar problem with that in a 260 (doughnuts forming on some, not all cases) when I expended them to 6.5mm. It showed up exactly as you described it - vertical on target, but probably not as bad a you described (I was turning cases which probably minimized the effect). Question: Does the base of your bullets extend beyond the neck/shoulder junction? Feel any difference in seating case to case or does seating get a little more difficult at the end of the seating stroke? Can you feel any "grabbiness" when the sizing ball on your sizer first contacts the neck while sizing? If the answer is yes to any of those, look closely for visual signs of doughnut formation.....

The cases and your bag technique are the only things held constant across your range of loads....... assuming your scope and mount are sound and your barrel is free-floated.

In my 7mm-08, I finally settled on Norma brass. Very uniform and nice thick necks (which I needed in a sloppy throat), but pricey.
ELkbane

 

[Rookie]

In addition, there's a host of variables that can induce vertical stringing. Here's a check list for evaluation: http://www.accurateshooter.com/shooting-skills/cures-for-vertical-stringing/

After reading the info on the link you posted I'm now thinking that my rifle is "unbalanced" , makes a lot of since, HS stock is lite as a feather and the barrel weighs 7lbs. I'm gonna add some weight to the butt of the rifle and give it a try.
Thanks for the info.

 

[WindSurgeon]

Adding weight to the butt stock will help your stability. I agree with the previouse assessment that all things being equal, a consistent vertical rise in the shots means that the barrel is heating and changing the point of impact. If it was a hold issue, it would be less consistently virtical and you would have windage issues and low and high shots. I have seen this heating issue with my AR with a heavy bull barrel. At about the 5th or 6th shot, it must reach a certain temperature it likes because it settles out at the higher point of impact, then is low again if the gun sits and cools for a while. It is not dramatic, but a noticeable change. The other item to worry about is your scope's ability to hold POI, but you did not mention the scope you have mounted on the gun and the mounting system. Cheap optics can ruin your day.

 

[Clark]

If the vertical string is sequential, it just keeps going higher, that can be caused by the barrel getting hot and pushing against the stock below that is pushing on it.

I like to have more clearance than a dollar bill that slides between the barrel and the stock, all the way back to the 1" of bedding in front of the recoil lug.

 

[BoydAllen]

How are you holding the rifle, and where are you placing the front bag on the stock? How much clearance between the stock and the barrel?

 

[Rookie]

First the Action and a 1" pad of barrel in front of the recoil lug are skim bedded with Devcon Ti epoxy, into a current Rem HS stock (with full Alum. skeleton) excellent job done by Smith. Barrel to stock gap is 3/32" .
PacNor Super match barrel, Pacnor trued the action and fitted the barrel using a ERP SS Super lug, and Tubb firing pin assembly.
Balance point for the rifle as/is is at the front sling swivel. Total weight of the rifle is 12lb with Leupold MkIV Boasted to 10x40 by Premier (from back when they did that), VERY front heavy.
Also Stock is a Rem HS Precision Varmint that dose not set well in the bag of my front rest or the rear bag .
The bench I'm shooting from isn't helping, it's a picnic table.
ES is 38fps SD is 26fps. with my best load - is 47.2 grs of H4350, 162 A-Max, with the bullets seated .010" off the lands.
After reading Speedy's wisdom I feel I need to balance the rifle, cure the lack of bag to stock fit issues, and work on my shooting skills before anything else. :-[

 

[queen_stick]

Rookie,

Keep in mind that it's all mechanical, with the exception of your loads and exterior conditions. There's something mechanically wrong, and you might be on the right path by changing the balance. Just be aware that weird things might happen when you start playing with different weights (balance), and bag setups.

I wouldn't have believed this if I didn't see it...
I found a nice 1K yard load for my 6BR (1K LG). It weighs about 16.2 pounds, so I decided to add a weight to the butt of the stock to get it closer to the 17lb limit. I added the appropriate weight to the rear of the stock, and at the same time I changed my front bag from leather to cordura. Using the same load that puts one hole in the paper at 100 yards, I couldn't get the gun to group under an inch at 100yards. (the groups were closer to 2"). I shot 3 5-shot groups, and all were well over an inch. I then took out the weight, and put my leather front bag back on the rest, and used my last 5 rounds to print a group in the .3's. It was an eye-opening experience for me. I simply changed the sandbag and balance of the rifle, and it sprayed lead like a shotgun. I removed the changes, and it went back hammerin' as it always has.

What I did not do was work up a new load with the added weight and new front bag. It's possible that a different laod will work with the added weight and new front bag. It's been in the plans for a while now, but I just got the gun back from my smith 2 days ago, so haven't had an opportunity to play with it.

Walt

 

[BoydAllen]

Where is the front bag on the stock, and how are you holding the rifle? Also, how did you pick the seating depth?

 

[SpencerC]

If you think you have exhausted all of the usual suspects, get someone else to shoot the rifle and see if it's the indian or the arrow....

 

[Hoier]

If you think you have exhausted all of the usual suspects, get someone else to shoot the rifle and see if it's the indian or the arrow....

+1