HOW CAN I IMPROVE SD/ED

[rchouser]

I have a 308 Win load that I am shooting at 1000 with good results (clay pigeons at 1000, not match shooting). It has an awful SD/ED (18.9 SD and 47 ED). This load is also grouping well at 100 and is a clay bird killer at 500.

I really don't know if I should mess with success, but, I guess I am going to. I am using CCI BR2 primers. I don't have any Federal 210M. I do have three other brands of standard LR primers. Should I just set up a few of each and chrono them?

Does seating depth affect SD/ED? I know jamming them would because of pressure. How about non-jammed changes to my current seating depth?

I am using a LEE collet die for neck sizing. I have found this really consistant. I do have a lee FCD (crimp die). I guess I could try a little crimp on it.

Any suggestions would be appreciated.

thanks in advance. rch

 

[Dusty Stevens]

Would you rather have results on paper or in theory?

 

[Jay Christopherson]

With that kind of ES, I wonder how you are measuring/dumping powder. I don't know of any other factors that affect to that degree - I've seen primers make a significant difference, but we're talking the difference between 18 or 19 and 11 or 12 maybe, not 47 to something-under-20.

 

[bpmoss1]

You asked if jamming may help. Depends where you are at currently. Jumped or jammed shouldn't cause fluctuations but touching sure can as its nearly impossible to make each bullet touch the same. The slightest bit either way means a seal or not and will definitely cause spreads. I either jump or jam by .005 or more to avoid.

 

[Mozella]

...... snip..............
I use an analytical balance and weigh to +/- half a kernel. Is that overkill? Probably, but I never have to worry about charge weight variance. .......snip.......

Wow......... that's impressive; half a kernel. My scale only has a .02gr resolution and am able (with some fiddling) to hit my target charge weight, plus zero, minus .02gr if I really work at it. I consider that pretty darn good, but my SD isn't always as small as I like. Do you think I need a better scale?

I tend to use short extruded powders so the kernels are pretty small. I have no idea how to cut a kernel in half. I can see them clearly with my flip down magnifier, but I don't see how you would hold a single kernel and I don't know what kind of knife you might use.

Perhaps two pairs of really teeny-tiny pliers to grab a kernel by each end and snap it in half. But then how would you get two equal half's? Maybe there is an easy way to score it in the middle.

Would that work, or do you have access to some kind of fancy microscope?

Or how about putting a teaspoon of powder in my coffee mill and wiz it around for a few seconds. That should break the kernels into smaller pieces which I could use when I needed to trickle up by half a kernel. Do you suppose there might be a danger of an explosion?

 

[Jay Christopherson]

...... snip..............
I use an analytical balance and weigh to +/- half a kernel. Is that overkill? Probably, but I never have to worry about charge weight variance. .......snip.......

Wow......... that's impressive; half a kernel. My scale only has a .02gr resolution and am able (with some fiddling) to hit my target charge weight, plus zero, minus .02gr if I really work at it. I consider that pretty darn good, but my SD isn't always as small as I like. Do you think I need a better scale?

I tend to use short extruded powders so the kernels are pretty small. I have no idea how to cut a kernel in half. I can see them clearly with my flip down magnifier, but I don't see how you would hold a single kernel and I don't know what kind of knife you might use.

Perhaps two pairs of really teeny-tiny pliers to grab a kernel by each end and snap it in half. But then how would you get two equal half's? Maybe there is an easy way to score it in the middle.

Would that work, or do you have access to some kind of fancy microscope?

Or how about putting a teaspoon of powder in my coffee mill and wiz it around for a few seconds. That should break the kernels into smaller pieces which I could use when I needed to trickle up by half a kernel. Do you suppose there might be a danger of an explosion?

A grain of <some_typical_powder_being_used_like_H4350> typically weighs between .025 - .035 grains, IME. Therefore, your resolution of .02 is plenty to let you know if you are plus or minus a kernel (or more) of powder. No one, that I am aware of who is still sane, cuts kernels of powder. A powder dispenser will sometimes cut a kernel when you cycle it.

EDIT: I realize you are being sarcastic or whatever, but some people, especially new shooters, might not get that. Not sure what point you were trying to make - just because gstaylorg's scale can measure to half a kernel, doesn't mean he is cutting kernels - a GD503 has a higher resolution than half a kernel and I don't think anyone is dumb enough to expect people are cutting trace amounts of propellant. But, it's easy to measure to half a kernel because not all kernels of powder are identical. You often get readings like 42.095 or 42.115. Get it?

 

[zipollini]

Some things that can improve sd/es

1. Powder weighing. Even though I use an analytical balance and weigh to +/- 1 kernel I think this is somewhat over kill.

2. Case preparation. I think this is where the most improvement can come from. (annealing, trimming, control inside neck chamfering depth and angle, uniform primer pockets, chamfer and deburr flash hole, polish inside neck chamfer, FL size and use neck bushing followed by polished expander mandril, control neck tension to a knats *** by measuring neck thickness and maybe skim turning necks

3. Bullet sorting by weight, bearing surface, base to ogive, etc.

4. Bullet lubrication in seating process (mica, graphite, dry moly or Hbn bullet coating). All my bullets are Hbn coated.

5. Choice of primers. I use Wolf large rifle primers for my 6XC.

6. Sort primers by weight

7. Measure seating pressure by using a 21st Century hydro press and sort finished cartridges by seating pressure.

8. Measure finished cartridge case base to bullet ogive and adjust and uniform if necessary.

9. Make sure your chronograph is reliable.

I shot 50 rounds of 6XC yesterday and my SD = 4.6 and my ES = 10.

 

[SteveOak]

I have a 308 Win load that I am shooting at 1000 with good results (clay pigeons at 1000, not match shooting). It has an awful SD/ED (18.9 SD and 47 ED).

I am one of those that will be supportive of you in your efforts. If it would make you happy to decrease the SD and ED (ES?), go for it. There are many pleasures to be had in our sport. I enjoy reloading as much as I do shooting as I see them as two parts of the same exercise rather then two different efforts. If it were only possible to purchase factory loaded ammunition my enjoyment would be significantly diminished. At the very least you will learn better reloading and data collection methods and habits, how to properly conduct an experiment and despite hysterical anecdotal proclamations to the contrary, what does work.

To that end, what SD and ES would you like to attain? From there you would be able to map out a path to achieve it. I like to go for SD of < 10 and an ES of < 25.

 

[dmoran]

What is your chronograph system and setup?
If your chronograph setup is not simulating what is happening in POI and accuracy terms on the targets to most all the shots (+85%), the ES/SD would be in error (no matter what brand or price tag).
Donovan

 

[savagedasher]

First thing to be done is to make sure what the internal volume of the case is. Without the internal capacity being the same it won't make any difference how accurate you meisure the powder or what neck tensions you have . Larry

 

[josebd]

are you using a beam scale or electronic scale for measuring powder?
i did not like the beam scale,electronic is the only way to go in my opinion
i have shot a little over 1/2 inch at 200 yards .223,5 shots,i know its not the best,but its the best ive done so far
i dont have a chronograph,so i wouldnt know about sd/ed,ive down pretty good with out it

 

[Steve Blair]

...... snip..............
I use an analytical balance and weigh to +/- half a kernel. Is that overkill? Probably, but I never have to worry about charge weight variance. .......snip.......

Wow......... that's impressive; half a kernel. My scale only has a .02gr resolution and am able (with some fiddling) to hit my target charge weight, plus zero, minus .02gr if I really work at it. I consider that pretty darn good, but my SD isn't always as small as I like. Do you think I need a better scale?

I tend to use short extruded powders so the kernels are pretty small. I have no idea how to cut a kernel in half. I can see them clearly with my flip down magnifier, but I don't see how you would hold a single kernel and I don't know what kind of knife you might use.

Perhaps two pairs of really teeny-tiny pliers to grab a kernel by each end and snap it in half. But then how would you get two equal half's? Maybe there is an easy way to score it in the middle.

Would that work, or do you have access to some kind of fancy microscope?

Or how about putting a teaspoon of powder in my coffee mill and wiz it around for a few seconds. That should break the kernels into smaller pieces which I could use when I needed to trickle up by half a kernel. Do you suppose there might be a danger of an explosion?

[br]
What Greg is saying is: [br]
If the target weight is 66.0 grains and the powder kernels weigh ~.0375 grains, then a measured weight of 65.98-66.02 grains produces a charge within half a kernel weight. This is very easily achieved without cutting or other unusual means. I do this on every charge. [br]
Greg is the current California Long Range F-TR champ, which he won with a fine-shooting .223 Rem. He, at least, has demonstrated that his methodology works. You?

 

[josebd]

good reading here

 

[BenPerfected]

First thing to be done is to make sure what the internal volume of the case is. Without the internal capacity being the same it won't make any difference how accurate you meisure the powder or what neck tensions you have . Larry

Larry,
More info please on how you measure the internal volume of cases. How many volume levels do you sort to? Can you manipulate the case to minimize the # of case sorts? Does your powder charge always remain the same regardless of case volume? I am concerned that there will be so many sorts that the complexity between neck tension sorts, bullet sorts, etc. will exceed my organization skills
Ben

 

[savagedasher]

Using QL as a reference 308 with Varget powder and 168 hybrid here is some numbers . With 2.80o cartridge length. no pressure added for touching the lands. 56.0 GR case capacity or 46.982 use case capacity with de duct for bullet seating capacity .
42.5 gr gives 2732 FPS and with 52515 PSI
42.6 gr gives 2736 FPS and with 52891 PSI a full tenth of a gr adds 4 fps and 376 psi
Seating depth change of.010 longer changes the FPS to 2733 a . tenth of a GR of powder is very close to a .010 of seating depth change.
A deviation of internal case capacity increase of a half GR which is very common. changes the bullet speed
with 42.5 to 2721 FPS which is 11 FPS difference.
That tells me internal case capacity is where I would look to lower ES and SD.
Larry

 

[savagedasher]

First thing to be done is to make sure what the internal volume of the case is. Without the internal capacity being the same it won't make any difference how accurate you meisure the powder or what neck tensions you have . Larry

Larry,
More info please on how you measure the internal volume of cases. How many volume levels do you sort to? Can you manipulate the case to minimize the # of case sorts? Does your powder charge always remain the same regardless of case volume? I am concerned that there will be so many sorts that the complexity between neck tension sorts, bullet sorts, etc. will exceed my organization skills
Ben

On my dasher I made a tool that I can check the capacity to a tenth of a grain or less ever time.
My good cases I have 5 FPS or less on ES with 10 shots. Crony error is bigger then then that.
in good condition I have shot many of group at 600 with 3/4 of vertical . Larry

 

[waldo1979]

What bullet and brass are you using? Are you looking at your group vertical offset (Cortina/OCW methods) when doing load development?

I was breaking in some new .308 brass last weekend and it averaged 7.6 SD.

 

[rchouser]

I am loading Lapua cases using charge_master 1500. Load is 44.2 gr Varget, CCI BR-2 primer and 175 SMK's. COAL is 2.808. Chronograph is a MagnetoSpeed v3.

I will sort cases and try again. I see one flyer in the string that drove the big ES. I will then go to the suggestions from all of you to see if I can tame this.

Thanks for all the help.

rch

 

[SteveOak]

.............. Anyone capable of multiplication/division can figure out exactly how much a given charge weight variance should affect velocity. ...........

I would be interested in seeing your calculations and how it worked out for you.

In my experience the relationship is non linear and velocity vs powder charge rises exponentially as the powder load volume approaches/becomes equal to the case volume.

 

[Sheldon N]

I would be interested in seeing your calculations and how it worked out for you.

In my experience the relationship is non linear and velocity vs powder charge rises exponentially as the powder load volume approaches/becomes equal to the case volume.

Quickload modeling indicates the relationship between charge weight and velocity is linear as you increase charges, all the way from 85% case fill up through 115% fill overpressure loads. (At least with Varget and 175 SMK's)