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Ranking loading variables to lower ES and SD

Florida Wally

Gold $$ Contributor
I’m working on reducing my vertical spread on the target. Factory Savage .308, 24” barrel, IMR 4064, Peterson brass tumbled in walnut media, CCI 200 lrp, 175 SMK at 2,490 fps average. I lubricate the bullet with graphite when seating and anneal brass each time fired. Using FL body die size and bump .001 to .003 and Lee collet for neck tension. Wilson inline arbor press to seat bullet. For 5 shot groups, I’m getting around a 0.75 moa vertical spread at 300 yards. ES‘s average in the high 20’s low 30’s and SD‘s average in the mid teens. When I do get low ES and SD, vertical reduces to half moa or less. I’m hoping that a consistently lower ES and SD will translate to lower vertical spread. Which of the following variables do you think is/are the most important to reduce ES and SD? I’m trying to figure out what process to more refine next.

1. Powder charge consistency
2. Bullet seating depth consistency
3. Primer
4. Shoulder bump consistency
5. Brass trim length
6. Projectile consistency - bullet sorting
7. Cartridge concentricity
8. Brass volume - sorting
9. Neck tension
10 Neck thickness consistency
11. Other

Thanks in advance!
 
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Of the items you listed, I'd suggest that consistent neck tension and using the appropriate primer should be very high on that list. Some of the other items in my hands don't seem to have a great deal of effect on velocity variance. For example, a reasonably good balance or tuned beam scale is more than capable of weighing powder with sufficient precision to provide single digit ES/SDs. Sorting bullets by weight typically has an effect on velocity that is too small to reliably measure with the chronographs we typically use. Items #4, 5, and 7, would all be considered part of doing meticulous brass prep, which should be routine. Taking and recording careful dimensional measurements of finished each brass prep is one way to ensure you have the consistency you're after from prep to prep. If not, it will usually help you troubleshoot where the problem lies.

One important consideration is that although we know that unacceptably high ES/SD can result in excessive vertical dispersion, it usually takes a much longer distance than 300 yd for that effect to reveal itself. I have a relatively new .223 Rem barrel in which I stupidly [accidentally] jammed a .30 cal cleaning rod into the throat. Although I cannot visually discern any problems with the barrel or chamber using a borescope, my handloads in that barrel have ridiculously high ES/SD values, sometimes as high as 60 to 80 fps ES for 5 shots, which is why I only use it as a fire-forming barrel. Nonetheless, that barrel is capable of shooting 10-shot groups at 334 yd of half a minute or less, even with the very high ES/SD values. The point is that it really takes a much longer distance before velocity variance becomes a major issue.

So the question you really might want to be asking is whether your velocity variance is the true culprit that is responsible for your vertical dispersion. Using a ballistic calculator with 175 SMKs at 2460 and 2490 fps, the predicted difference in drop at 300 yd solely due to velocity variance is well under 0.2 MOA (0.16 MOA). There are certainly other variables that can cause excessive vertical, including certain wind conditions, the load itself, or the shooter behind the rifle. My first thought would be to take another look at seating depth, preferably at 300 yd, if that is the distance you shoot most often. It may well be that a simple seating depth test will allow you to tune the load a little better with respect to minimizing vertical dispersion. If you take that approach, be sure to do the testing under the most minimal wind conditions possible, and put out wind flags so you have some idea what the conditions are while shooting. There is nothing wrong with improving/enhancing your brass prep or other reloading methods, but it's easy to go pretty far down that rabbit hole with little to show for it, if those weren't the causative issues to begin with.
 
I’m working on reducing my vertical spread on the target. Factory Savage .308, 24” barrel, IMR 4064, Peterson brass tumbled in walnut media, CCI 200 lrp, 175 SMK at 2,490 fps average. I lubricate the bullet with graphite when seating and anneal brass each time fired. Using FL body die size and bump .001 to .003 and Lee collet for neck tension. Wilson inline arbor press to seat bullet. For 5 shot groups, I’m getting around a 0.75 moa vertical spread at 300 yards. ES‘s average in the high 20’s low 30’s and SD‘s average in the mid teens. When I do get low ES and SD, vertical reduces to half moa or less. I’m hoping that a consistently lower ES and SD will translate to lower vertical spread. Which of the following variables do you think is/are the most important to reduce ES and SD? I’m trying to figure out what process to more refine next.

1. Powder charge consistency
2. Bullet seating depth consistency
3. Primer
4. Shoulder bump consistency
5. Brass trim length
6. Projectile consistency - bullet sorting
7. Cartridge concentricity
8. Bullet seating lubrication
9. Neck tension
10 Neck thickness consistency
11. Other

Thanks in advance!

It doesn't seem that long ago I was where you are in terms of ES's and SD's. And before I answer your question, one of the things I came across that helped me understand what I was dealing with for my .308 is that (though it's a popular cartridge) it's one that's somewhat difficult to get ES and SD numbers that we see with those for 6 or 6.5 mm's. Even so, I set out a goal to get my .308 cartridge's SD's into the single digits with some reasonable ES's at the mid teens or maybe a little better. I'm happy to report that I've achieved those goals and my tuned loads group very consistently under .4 MOA (sometimes under .3 and sometimes just under .5 MOA).

Powder charge accuracy along with consistency is the largest factor. If one has a scale that can measure to the .02 grs where the difference in a kernal of power can been see, it'll help greatly in getting low SD's.

Along with accurate/consistent powder charges is the case volume in which the powder resides. It too needs to be consistent. The volume where the powder resides is determined by several factors: Seating depth is the primary one; Quality brass that has consistent volume (mass production of cases along with little attention to quality control, produces cases with substantial variances); Sizing consistency, like getting the shoulder to the same place.

Next, is bullet selection where one uses high quality match grade bullets so that the dimensions and weights have little variation.

If you get just these three things, you're SD's and ES's will do very well. But there's always room for minor improvements and that's where things like Neck Tension, Seating Resistance, Primers, Neck Thickness and Concentricity can help. And I might add that I've found that annealing helped me a lot in making my .308 cases more consistent in getting more consistent seating, shoulder bumps and concentricity.

One other thing I always do in my case prepping is I alway trim them to the same length as the last step in my prep procedures. I can't say I can see any difference in my numbers or on paper. But I feel in always keeping them the same length I don't worry about any carbon ring build up that might effect consistency. I'm just a little anal about trying to keep EVERYTHING as uniform as possible. ;) That way, when I see a POI where it's not supposed to be, I have nothing to blame but the nut that pulled the trigger. :eek::cool: These days I'm working on trying to read the wind better to get more consistent results.
 
Of the items you listed, I'd suggest that consistent neck tension and using the appropriate primer should be very high on that list. Some of the other items in my hands don't seem to have a great deal of effect on velocity variance. For example, a reasonably good balance or tuned beam scale is more than capable of weighing powder with sufficient precision to provide single digit ES/SDs. Sorting bullets by weight typically has an effect on velocity that is too small to reliably measure with the chronographs we typically use. Items #4, 5, and 7, would all be considered part of doing meticulous brass prep, which should be routine. Taking and recording careful dimensional measurements of finished each brass prep is one way to ensure you have the consistency you're after from prep to prep. If not, it will usually help you troubleshoot where the problem lies.

One important consideration is that although we know that unacceptably high ES/SD can result in excessive vertical dispersion, it usually takes a much longer distance than 300 yd for that effect to reveal itself. I have a relatively new .223 Rem barrel in which I stupidly [accidentally] jammed a .30 cal cleaning rod into the throat. Although I cannot visually discern any problems with the barrel or chamber using a borescope, my handloads in that barrel have ridiculously high ES/SD values, sometimes as high as 60 to 80 fps ES for 5 shots, which is why I only use it as a fire-forming barrel. Nonetheless, that barrel is capable of shooting 10-shot groups at 334 yd of half a minute or less, even with the very high ES/SD values. The point is that it really takes a much longer distance before velocity variance becomes a major issue.

So the question you really might want to be asking is whether your velocity variance is the true culprit that is responsible for your vertical dispersion. Using a ballistic calculator with 175 SMKs at 2460 and 2490 fps, the predicted difference in drop at 300 yd solely due to velocity variance is well under 0.2 MOA (0.16 MOA). There are certainly other variables that can cause excessive vertical, including certain wind conditions, the load itself, or the shooter behind the rifle. My first thought would be to take another look at seating depth, preferably at 300 yd, if that is the distance you shoot most often. It may well be that a simple seating depth test will allow you to tune the load a little better with respect to minimizing vertical dispersion. If you take that approach, be sure to do the testing under the most minimal wind conditions possible, and put out wind flags so you have some idea what the conditions are while shooting. There is nothing wrong with improving/enhancing your brass prep or other reloading methods, but it's easy to go pretty far down that rabbit hole with little to show for it, if those weren't the causative issues to begin with.
Thanks for the response and tips. I have only tested seating depth at 100 yards. I will try at 300 yards and see if i can reduce vertical. Your explanation is certainly compelling.
 
It doesn't seem that long ago I was where you are in terms of ES's and SD's. And before I answer your question, one of the things I came across that helped me understand what I was dealing with for my .308 is that (though it's a popular cartridge) it's one that's somewhat difficult to get ES and SD numbers that we see with those for 6 or 6.5 mm's. Even so, I set out a goal to get my .308 cartridge's SD's into the single digits with some reasonable ES's at the mid teens or maybe a little better. I'm happy to report that I've achieved those goals and my tuned loads group very consistently under .4 MOA (sometimes under .3 and sometimes just under .5 MOA).

Powder charge accuracy along with consistency is the largest factor. If one has a scale that can measure to the .02 grs where the difference in a kernal of power can been see, it'll help greatly in getting low SD's.

Along with accurate/consistent powder charges is the case volume in which the powder resides. It too needs to be consistent. The volume where the powder resides is determined by several factors: Seating depth is the primary one; Quality brass that has consistent volume (mass production of cases along with little attention to quality control, produces cases with substantial variances); Sizing consistency, like getting the shoulder to the same place.

Next, is bullet selection where one uses high quality match grade bullets so that the dimensions and weights have little variation.

If you get just these three things, you're SD's and ES's will do very well. But there's always room for minor improvements and that's where things like Neck Tension, Seating Resistance, Primers, Neck Thickness and Concentricity can help. And I might add that I've found that annealing helped me a lot in making my .308 cases more consistent in getting more consistent seating, shoulder bumps and concentricity.

One other thing I always do in my case prepping is I alway trim them to the same length as the last step in my prep procedures. I can't say I can see any difference in my numbers or on paper. But I feel in always keeping them the same length I don't worry about any carbon ring build up that might effect consistency. I'm just a little anal about trying to keep EVERYTHING as uniform as possible. ;) That way, when I see a POI where it's not supposed to be, I have nothing to blame but the nut that pulled the trigger. :eek::cool: These days I'm working on trying to read the wind better to get more consistent results.
Thanks for the advice. Narrowing my focus to a few processes is exactly what I was hoping I would achieve with this post. The three things you mention will help keep me from going too deep into the rabbit hole.
 
Interesting thread. I'm working on this with my rifles. I can get 1/4 moa with a particular load in my .223. ES will 7 or 8. Then, next time I shoot the same load, ES is 40 and the groups open up to 1/2 moa. I will have one round in each 5 shot string that is either fast by 30 fps or slow by 30 fps. Same brass, powder charge, lot. Same bullet, seating depth, same primer, lot. Brass prep is the same including cleaning and annealing. I use Wilson in-line seaters with a K&M arbor press with a standard force pack installed. Seating force is between 18 and 22 lbs. I weigh each charge. I don't have a mechanical scale to check my digital scale against. I do have a 2nd digital scale that I have verified my main scale with.
 
Let’s do the ballistics. If your extreme spread is 30 fps, then we want to look at the drop for the upper and lower extremes. Using my handy dandy ballistics calculator for your SMK 175 at 300 yards:

Velocity Drop (in) Drop (moa)
2475 -18.2. -5.8
2490 -17.9 -5.7
2505 -17.6 -5.6

The vertical difference between the two extremes is .6 inches or 0.2 moa (slightly less than one quarter moa). This would only account for a small part of your vertical stringing of 0.75 moa. I think you have to consider that your technique could be part of the problem. I would look at your breathing. If you have too much air in your lungs you will impact high; if you have too little air in your lungs you will impact low. You want to pause near the low point of your breathing cycle, but not at the bottom. I believe this might explain the other 0.5 moa in your vertical stringing.
 
That's a lot of vertical. Have you found a stable node with minimal vertical across a band of powder charges that you're loading in?

You may find my load development process interesting: https://forum.accurateshooter.com/threads/my-new-22br.3981971/post-37830982

It seems like there is a bigger problem afoot here. Particularly if the rifle shoots significantly smaller than 0.75MOA at 100 and then opens up at 300. Do you use wind flags? Is your range square and flat? I shoot out in the grasslands where wind blowing over uneven terrain introduces vertical to groups and not just horizontal spread.
 
How did you perform your load work-up to this point? Were you using a Chronograph to look for flat spots, or did you look for vertical on a target?

It almost sounds like you're not in a node to begin with.

As to how much things matter, you might be a little surprised....

I've shot cleans at 600 with multi-time fired Palma brass that wasn't annealed, wasn't turned, wasn't expanded, wasn't trimmed, just bushing sized, thrown on a charge master, and had depth vary ~.002-.003 across the batch.

That's not to say I do that regularly (quite the opposite actually), but there's a LOT to be said for identifying the middle of a depth node and charge node.
 
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That's a lot of vertical. Have you found a stable node with minimal vertical across a band of powder charges that you're loading in?

You may find my load development process interesting: https://forum.accurateshooter.com/threads/my-new-22br.3981971/post-37830982

It seems like there is a bigger problem afoot here. Particularly if the rifle shoots significantly smaller than 0.75MOA at 100 and then opens up at 300. Do you use wind flags? Is your range square and flat? I shoot out in the grasslands where wind blowing over uneven terrain introduces vertical to groups and not just horizontal spread.
A have found a node with minimal vertical, but a consistent load is what I am searching for. I have found a node at 38.1 to 38.4 grains that in testing twice produced an ES of 9. I load at 38.3 grains. Seating depth testing with that load produced a node at .025 -.028 off of jam. I load at .027 off the lands. Problem is achieving consistency through 50 rounds that will maintain acceptable ES/SD hopefully leading to less vertical. The range is flat and surrounded by berms/trees on three sides which can cause a swirling wind, but I have been intentionally shooting in the morning when there is little wind to remove that variable. When the ES is low, the vertical does improve. Your method does look interesting, and if I can achieve an acceptable ES, I will try it. I’m a little concerned about approaching max pressure with a my current inconsistent ES. I need to remove some loading variables first.
 
How did you perform your load work-up to this point? Were you using a Chronograph to look for flat spots, or did you look for vertical on a target?

It almost sounds like you're not in a node to begin with.

As to how much things matter, you might be a little surprised....

I've shot cleans at 600 with multi-time fired Palma brass that wasn't annealed, wasn't turned, wasn't expanded, wasn't trimmed, just bushing sized, thrown on a charge master, and had depth vary ~.002-.003 across the batch.

That's not to say I do that regularly (quite the opposite actually), but there's a LOT to be said for identifying the middle of a depth node and charge node.
Thanks Mike, I almost exclusively shoot over a chrony and did find nodes. I used the chrony to determine charge weight node and seating depth to determine accuracy node. When ES is low those nodes shoot good. Unfortunately, I can’t produce low ES through 50 rounds. I am hoping to begin eliminating variables one at a time and achieve acceptable ES which I think will lower vertical spread. Other posts have me wondering by how much, but I need to fix one thing at a time or I’ll never know.
 
I mean, if your powder charges are under control, say +/- 0.1gns, then I'd start looking at the rifle. Are you having ignition issues? Is the firing pin dragging, is the spring weak, etc. Inconsistent ignition wreaks havoc on accuracy.

Another possibility is primers, although I think this is highly unlikely and unfortunately you can't just go buy a variety of different primers right now to see if the gun strongly dislikes 200s for some reason.
 
Thanks Mike, I almost exclusively shoot over a chrony and did find nodes. I used the chrony to determine charge weight node and seating depth to determine accuracy node. When ES is low those nodes shoot good. Unfortunately, I can’t produce low ES through 50 rounds. I am hoping to begin eliminating variables one at a time and achieve acceptable ES which I think will lower vertical spread. Other posts have me wondering by how much, but I need to fix one thing at a time or I’ll never know.

Just as a test, before you drop $10,000 on a whole new reloading room, go find your nodes based off vertical. Ignore the ES/SD.

I'd bet good money you'll wind up in a different powder charge node.
 
Let’s do the ballistics. If your extreme spread is 30 fps, then we want to look at the drop for the upper and lower extremes. Using my handy dandy ballistics calculator for your SMK 175 at 300 yards:

Velocity Drop (in) Drop (moa)
2475 -18.2. -5.8
2490 -17.9 -5.7
2505 -17.6 -5.6

The vertical difference between the two extremes is .6 inches or 0.2 moa (slightly less than one quarter moa). This would only account for a small part of your vertical stringing of 0.75 moa. I think you have to consider that your technique could be part of the problem. I would look at your breathing. If you have too much air in your lungs you will impact high; if you have too little air in your lungs you will impact low. You want to pause near the low point of your breathing cycle, but not at the bottom. I believe this might explain the other 0.5 moa in your vertical stringing.
Yes, great point. You have me thinking now about breathing. I tend to break the shot with little air in my lungs. I’ll can work on that while I am working on consistent loads.
 
Just as a test, before you drop $10,000 on a whole new reloading room, go find your nodes based off vertical. Ignore the ES/SD.

I'd bet good money you'll wind up in a different powder charge node.
Chronos just feel so mathematical and statistically sound but it's an illusion. I tried to use one to develop a load for a barrel a few years ago and ended up in the weeds for 400+ rounds before I put it away and went back to the method of looking at vertical at distance to find my powder charge.

I agree with Mike. I bet you'd end up somewhere else entirely if you started again without the chrono.

Looking at vertical on the target at distance encompasses the whole system of combustion and ballistics and evaluates it at the end point. A chrono is an instrument with its own sources of errors, evaluating one property of the whole system in the middle, after it's left the barrel but before it has made its flight to the target.
 
Just as a test, before you drop $10,000 on a whole new reloading room, go find your nodes based off vertical. Ignore the ES/SD.

I'd bet good money you'll wind up in a different powder charge node.
OK. I’ll test using vertical only and go from there. I’m about to load them now to shoot this weekend.
 
it's not as simple as having consistent weights, it's having consistent weights of the proper charge weight of the proper powder. In my experience doing load tweaking I look for a charge where I can go up or down .1 gns on a node and the velocity difference will be negligible
 

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