vertical stringing, Load, rifle or me?

[Nature Boy]

What's going on with this 10 round group at 100 yards? What would you do to tighten it up? Squares are 1"

.308win, 185 Juggernaut, 43.7g of Varget, Lapua brass, 210m primer, .016 off the lands, 2,690 FPS, SD 9

 

[hrlincoln]

Not sure what your setup is, but here's an article listing some possibilities.

http://www.accurateshooter.com/shooting-skills/cures-for-vertical-stringing/

 

[swadiver]

I shot 43.5 grs of Varget in Lapua and CCI BR2 primers with no stringing like that. i used .015" off the lands. try plus/minus .2's of a grn of powder. could also be be shooter technique, recoil control?

 

[Nature Boy]

Not sure what your setup is, but here's an article listing some possibilities.

http://www.accurateshooter.com/shooting-skills/cures-for-vertical-stringing/

What a great article. I think the first point mentioned may be the biggest culprit

Barrel Weight–A lot of rifles are muzzle-heavy. Some rifles have too heavy a barrel and this causes vertical, especially when shooting free recoil. Basically the gun wants to tip forward. The remedy is to trim or flute the barrel, or add weight in the rear (if you can stay within weight limits).

The rifle is pretty front heavy with an MTU contour 26" barrel

That said, I probably have a little bit of all of those issues going on

 

[ImBIllT]

Change the powder charge. If it continues to string, then it's not the load.

If stringing ceases when you can he the powder charge, then return to the same powder charge, if it begins to string again, then it might be the load.

Close range vertical stringing CAN be a result of shooting a velocity such that the barrel was on the downward moving portion of its vibration when the bullets exit the barrel. When this is the case, even small velocity variations can cause vertical spread because slightly fast shots exit when the barrel is pointing up and slightly slow shots exit when it is pointing down. If you change the velocity such that the bullet exits while the barrel is changing direction between going up and going down, you can have a much larger velocity spread result is much less vertical. This is what short range ladder tests identify. This effect dissipates greatly as range changes. Many short range shooters claim their best loads at 100yds have high velocity spreads and aren't nearly their best loads at 200-300yds. It just happens that the most consistent loads for their gun fail to land on a 100yd node. For F-class or other long range disciplines, tuning primarily at ranges other than 100yds can be more productive because you won't dealing with the variables that make 100yds finicky, and you won't find yourself accidentally messing with one of those loads that only works great at 100.

 

[T-shooter]

Change the powder charge. If it continues to string, then it's not the load.

If stringing ceases when you can he the powder charge, then return to the same powder charge, if it begins to string again, then it might be the load.

Close range vertical stringing CAN be a result of shooting a velocity such that the barrel was on the downward moving portion of its vibration when the bullets exit the barrel. When this is the case, even small velocity variations can cause vertical spread because slightly fast shots exit when the barrel is pointing up and slightly slow shots exit when it is pointing down. If you change the velocity such that the bullet exits while the barrel is changing direction between going up and going down, you can have a much larger velocity spread result is much less vertical. This is what short range ladder tests identify. This effect dissipates greatly as range changes. Many short range shooters claim their best loads at 100yds have high velocity spreads and aren't nearly their best loads at 200-300yds. It just happens that the most consistent loads for their gun fail to land on a 100yd node. For F-class or other long range disciplines, tuning primarily at ranges other than 100yds can be more productive because you won't dealing with the variables that make 100yds finicky, and you won't find yourself accidentally messing with one of those loads that only works great at 100.

Right, work with the powder load. I've had them string vertically, and increasing the load it will go round or maybe even horizontal a little and as the load increases, back to vertical again. No more than 2/10 grain per change and at least 5 shots per step. When you find the best group, work on the jump. One test I did at 100 yards was to adjust the jump from .005" to .030". I shot one shot into each group and then started over, 6 times letting the barrel have time to cool in between. Once you think you have found the riht combination, shoot at least 10 into a group to confirm. This was with Lapua cases, Federal Match primers, 41.7 grains of IMR4064 and Hornady 168 grain BTHP match bullets. The Sierra 168 M/K also shoot well with this load.

 

[Nature Boy]

I'm headed toward the lower side now. 43.7g of Varget is at the pressure limit

Here's my "cortina method" target

 

[CharlieNC]

It's difficult not to dismiss the shooter influence. Looking at your setup, you have a tapered stock butt running on a tapered rear bag ( which is setup with the taper backwards to the stock ). For me it is not uncommon when shooting a similar rig to shoot high when I have poor recoil management. Shooting a Harris bipod, loading it a bit helps tame this as well. In your case I can see if you do not manage the recoil the same every time that the rifle will recoil to various degrees, meaning the influence on the butt taper varies. Have you tried reversing the bag so it's angle matches that of the stock? Do you get much muzzle jump? But the change to horizontal with the 44.0 charge is interesting regarding load influence.

 

[T-shooter]

I'm headed toward the lower side now. 43.7g of Varget is at the pressure limit

Here's my "cortina method" target

I don't like 3 round groups, I think 5 is minimum. Somehow I have the same thing happen as you, pairs of touching shots. Is that accuracy or random luck? Here is a strange one. This was 208 grain A-Max at 215 yards and I don't know in what order they hit. Even 6 shots here didn't tell me anything.

Here are a couple 10 shot groups from a couple years ago at 100 yards. Not the tightest but all in the same area. This was when I was using a beam scale instead of a digital and the powder loads probably weren't as close.

 

[Nature Boy]

Thanks to all of you that responded here or sent some good advice via PM. I believe it all helped. As with most issues, it's never one thing. I think there's 2 main factors 1) the load and 2) my technique. I changed both and here's what I got. 1" target dots, 5 shots each. Original 43.7 load on the left, 43.5 in the middle and 43.0 on the right.

I removed the carpet from under the rest so the spikes contacted the concrete bench. I removed the small bag in the front and flipped the rear bag around. I paid particular attention to consistent interface with the rifle. Recoil became more consistent front to back and so did the results

I was rewarded with a 5 shot group that I was almost able to get through the same hole. I stopped on that one

Thanks again for the advice everyone. It was all very helpful

 

[Nature Boy]

The 185 Bergers did not hold up at longer distances but the 180 SMKs did. Here's my 5 shot group with 180 SMKs at 1,000 yards

 

[rayjay]

Hopefully you are not actually shooting from the bench with that sling hanging off the side...... Also, run your rest leveling screws out much further and then you will be able to lower the center post that same amount. Pay close attention to getting the parallax set correctly for the distance you are shooting. The numbers on the adjuster are just a close guideline.

 

[T-shooter]

The 185 Bergers did not hold up at longer distances but the 180 SMKs did. Here's my 5 shot group with 180 SMKs at 1,000 yards

Now that's just plain showing off! Just kidding, great shooting. I'd feel real lucky just to hit the steel at that distance.