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Tuning out vertical

Florida Wally

Gold $$ Contributor
I’m shooting .308 out of a 30” barrel. Shooting Berger 200-20x and I think I found a powder node where 3 shot groups of 42.6 grs of Varget and 42.9 grs of Varget shot at the same elevation on target. I loaded 10 rounds at .009 off the lands (where I tested the powder) with 42.8 grs to verify the node and shot two 5 round groups to verify. With the exception of one flyer, the two groups landed at the same elevation on the target. Avg velocity was 2650 FPS. The groups however, have around .400 vertical and are around .500 moa accounting for the flyer.

My question is, will I be able to tune some of the vertical out with seating depth, or should I do some more powder testing before I go to seating depth testing?
 
Regardless of group sizes or relative elevation on the targets, use charge weight testing to identify a window with minimal ES/SD. Then tune group size/shape using seating depth. Unless you carried out the initial charge weight testing at 300+ yd, minor elevation changes of the groups on the target could be a lot of things. As long as you have correctly identified the middle of an optimal charge weight window, tuning in the group size/shape with seating depth adjustment should be straightforward. Once you have done that, test a longer string (i.e. 15-20 shots) at a longer distance, such as 600 yd, to validate that the load is performing as expected; i.e. acceptable ES/SD and precision.

In the event that the ES/SD and/or the precision don't hold up for the longer string of fire at greater distance, it may be necessary to re-visit charge weight testing and follow up with additional seating depth testing to at least confirm that any subsequent changes you may find it necessary to make in charge weight haven't affected the previously identified seating depth optimum. Excessive vertical can be due to a number of different things including brass prep (i.e. neck tension as 47WillysGuy suggested), not getting the charge weight quite right, the actual seating depth used during charge weight testing being substantially off from "optimal", or even simple shooter error, among others. Until you determine what optimizing seating depth will do for the group size/shape, it's sometimes difficult to determine which of these factors may be the major cause(s) of vertical stringing. However, when you carry out a seating depth test and identify a couple successive seating depth increments where the groups tighten up nicely, then you have the answer.

Due to the number of variables that go into load development, it can sometimes be difficult to determine an exact underlying cause for some behavior observed on the target when you're at an intermediate stage of the process. Based on the velocity you're obtaining with the 200.20X out of a 30" barrel, I would guess you're pretty close to where you want to be with charge weight. With the combination of Varget, 200.20Xs, and a 30" barrel, I'd try seating depth testing next, covering a range from (at least) .003" off to .015" off in .003 increments and see what that does for you.
 
You are in the ball-park on your "avg" velocity . And as Ned said , A longer string at greater distance should give you more useable data . Look at your current data , also . were there any rounds that were higher than....or Lower than.....your avg. velocity , by more than slight deviation . When I run these tests , and find a nice grouping load at 100 , I load 10 with + .02 , 10 at +.04 , and ten at +.06 in a short ladder and shoot them at 600 on a calm day . Using the same seating depth on all loads . Sometimes you get the answer you need before shooting all the rounds , from a particular load . The short ladder will also help keeping velocity on target at the longer distance , also .
 
Regardless of group sizes or relative elevation on the targets, use charge weight testing to identify a window with minimal ES/SD. Then tune group size/shape using seating depth. Unless you carried out the initial charge weight testing at 300+ yd, minor elevation changes of the groups on the target could be a lot of things. As long as you have correctly identified the middle of an optimal charge weight window, tuning in the group size/shape with seating depth adjustment should be straightforward. Once you have done that, test a longer string (i.e. 15-20 shots) at a longer distance, such as 600 yd, to validate that the load is performing as expected; i.e. acceptable ES/SD and precision.

In the event that the ES/SD and/or the precision don't hold up for the longer string of fire at greater distance, it may be necessary to re-visit charge weight testing and follow up with additional seating depth testing to at least confirm that any subsequent changes you may find it necessary to make in charge weight haven't affected the previously identified seating depth optimum. Excessive vertical can be due to a number of different things including brass prep (i.e. neck tension as 47WillysGuy suggested), not getting the charge weight quite right, the actual seating depth used during charge weight testing being substantially off from "optimal", or even simple shooter error, among others. Until you determine what optimizing seating depth will do for the group size/shape, it's sometimes difficult to determine which of these factors may be the major cause(s) of vertical stringing. However, when you carry out a seating depth test and identify a couple successive seating depth increments where the groups tighten up nicely, then you have the answer.

Due to the number of variables that go into load development, it can sometimes be difficult to determine an exact underlying cause for some behavior observed on the target when you're at an intermediate stage of the process. Based on the velocity you're obtaining with the 200.20X out of a 30" barrel, I would guess you're pretty close to where you want to be with charge weight. With the combination of Varget, 200.20Xs, and a 30" barrel, I'd try seating depth testing next, covering a range from (at least) .003" off to .015" off in .003 increments and see what that does for you.
Thanis, this is what I was hoping to hear. I’ll try starting at .003 off and move back by .003 increments.
 
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You are in the ball-park on your "avg" velocity . And as Ned said , A longer string at greater distance should give you more useable data . Look at your current data , also . were there any rounds that were higher than....or Lower than.....your avg. velocity , by more than slight deviation . When I run these tests , and find a nice grouping load at 100 , I load 10 with + .02 , 10 at +.04 , and ten at +.06 in a short ladder and shoot them at 600 on a calm day . Using the same seating depth on all loads . Sometimes you get the answer you need before shooting all the rounds , from a particular load . The short ladder will also help keeping velocity on target at the longer distance , also .
Interesting approach. I think I’ll try this as well as Ned’s suggestion.
 
If you can measure your ES and identify the speeds on target, you might find your reason for the vertical. 1fps equals .1 at 600 yards. How to fix this is complicated and the advice given is all good. But, I’d start with neck tension and seating depth.
 
The lowest ES doesn't always correspond to the smallest group. In fact, it rarely does. I think ES is more of an indication of how well our loading technique works.

Groups size is what matters.

A good tuning node can easily allow 20-30 fps variation in velocity and will still print to the same POI at long range.

Generally, powder charge gets us close then we refine with seating depth. Then neck tension. Then maybe we recheck powder.

That is assuming we are close to where we want to be.
 
I’m shooting .308 out of a 30” barrel. Shooting Berger 200-20x and I think I found a powder node where 3 shot groups of 42.6 grs of Varget and 42.9 grs of Varget shot at the same elevation on target. I loaded 10 rounds at .009 off the lands (where I tested the powder) with 42.8 grs to verify the node and shot two 5 round groups to verify. With the exception of one flyer, the two groups landed at the same elevation on the target. Avg velocity was 2650 FPS. The groups however, have around .400 vertical and are around .500 moa accounting for the flyer.

My question is, will I be able to tune some of the vertical out with seating depth, or should I do some more powder testing before I go to seating depth testing?

 
Last edited:
If you can measure your ES and identify the speeds on target, you might find your reason for the vertical. 1fps equals .1 at 600 yards. How to fix this is complicated and the advice given is all good. But, I’d start with neck tension and seating depth.
Just don’t put a great deal of stock into the speed on the target from the e-targets
Dave
 
If you can't seem to find a sweet spot don't be afraid to back off from the lands, a lot. I have a couple of rifles that really love a huge jump like .050 or more. My 6.5x47 is really happy at .073 off the lands.
 
If you can't seem to find a sweet spot don't be afraid to back off from the lands, a lot. I have a couple of rifles that really love a huge jump like .050 or more. My 6.5x47 is really happy at .073 off the lands.
Yes. I was talking to a really good shooter at a match and he mentioned this. i never test past .030 off.
 
What neck tension you running for your 20x load
As for seating depth with .308 and 20x bullet you should find a sweetspot between 10 to 17 thousands Off the Lands.
 
Yes. I was talking to a really good shooter at a match and he mentioned this. i never test past .030 off.
I really kinda hope my rifle likes loads way off the lands. If the bullets are seated way off then seating depth is not an issue anymore and one less thing to worry about. My new 22 BR shoots real well with 77gr match kings and it has a really wide seating window, .040 to .055 so I'm loading them at .045 and running with it. However the Hornady 75gr HPBT's only like .010 off and a very narrow window. Try a few groups at .030, .040, .050, .060, .070 and see,... maybe, maybe not.
 
If you can't seem to find a sweet spot don't be afraid to back off from the lands, a lot. I have a couple of rifles that really love a huge jump like .050 or more. My 6.5x47 is really happy at .073 off the lands.
I have a 6.5x47 repeater with .167 freebore and a single shot with .225 , I shot some ammo one day in the single shot loaded for the repeater that worked out to a .065 jump that has become the best load I’ve got in that rifle. 40.5 H4350 and 130 VLDH at .065 off
 
What neck tension you running for your 20x load
As for seating depth with .308 and 20x bullet you should find a sweetspot between 10 to 17 thousands Off the Lands.
I use a bushing to size the neck to 0.305 then use a .3075 mandrel twice, so I have about .001 to .0015 interference fit after springback.
 
I really kinda hope my rifle likes loads way off the lands. If the bullets are seated way off then seating depth is not an issue anymore and one less thing to worry about. My new 22 BR shoots real well with 77gr match kings and it has a really wide seating window, .040 to .055 so I'm loading them at .045 and running with it. However the Hornady 75gr HPBT's only like .010 off and a very narrow window. Try a few groups at .030, .040, .050, .060, .070 and see,... maybe, maybe not.
I was thinking something like .30, .35, .40 ... up to .60 or .70. It’s worth a try. Hopefully I’ll find a wide window like you mention.
 

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