Top three things to reduce ES and SD

[craigp40]

What are the top 3 things you guys do when trying to reduce extreme spread and standard deviation? I've got a rifle that is shooting some pretty decent groups, but my ES and SD are quite high. Granted, I don't have the best chronograph, so maybe that's the problem... But for now, let's focus on reloading techniques.

 

[papa45]

Do't mix components.

Don't mix batches.

Weigh every powder charge exactly.

 

[Hired Gun]

One shot groups really cuts it down. /ubbthreads/images/graemlins/grin.gif
Seriously, using a powder that fills the case as full as possible. Even slightly compressed is very good for ES. Even neck tension. I stay well away from the lands to avoid pressure spikes from that and I use magnum primers in everything.

 

[craigp40]

I do almost all of those, except the mag primers. HG, do you really notice a difference (accuracy and chrono results) using mag primers over standard? The cartridge I'm working with is a custom 7-08, but I haven't tried mag primers yet.

 

[Hired Gun]

Yes, I find a solid ignition much more consistant than a marginal one. I chronogrph everything. I even use CCI-250's in my 22-250.

 

[goodgrouper]

When doing load development, there will most likely be a low end sweet spot and a high end sweet spot in the pressure curve with large extreme spreads and deviations inbetween. Then once you go beyond the high end spot, the SD and ES will begin to get larger again. Almost all powders will exhibit this trait but some will yeild better accuracy than others while running through the testing.

It all boils down to a huge variety of things that determine how the internal ballistics will turn out, but all you will need to do most times is change one or more of the four components if the accuracy associated with the good deviation nodes is unsatisfactory.

 

[6BR4ME2]

It all boils down to you and what the gun will shoot on paper. Too often ES and SD are not what will give your most consistant load ...and this will vary from yardage to yardage also...so it sounds like you allready have a good load now only go up or down 3 tenths of a grain and see if it opens up or gets better. The load your using now is a great place to start then test it. Almost all bullet powder combinations have two accuracy "nodes" usually at the high end of pressure and velocity and the other at a lower node ...so good luck and try it ...

 

[sambo3006]

[ QUOTE ]
Too often ES and SD are not what will give your most consistant load

[/ QUOTE ]

True sometimes for precision at short yardage but I would think that large ES/SD even with an accurate load would start to give you vertical stringing as yardage increases. Probably not noticable at 300-400 yds but it would start to add up. Just a thought.

 

[6BR4ME2]

shooting small groups at whatever range is the key...if you had a very small group...I'm talking about a 1000yds by the way not 300 or 400 and your ES or SD was high I would take the small group any day and run with it...if your load is what your barrel likes and is tuned it will compensate for your crony numbers..again go shoot that "good" load and see what it can do with your .3 grn changes in powder and go from there....good luck...go with what your small groups tells you!!!!

 

[LRHWAL]

Haven't tested it myself, but I've read - and seen a recent post here if I recall - that standard primers (as opposed to mag's) will often give better ES and SD.... so there you go, no clear answer. Which is why we keep tinkering forever /ubbthreads/images/graemlins/grin.gif

 

[remingtonman_25_06]

Some rifles likes mag primers, some dont. Only way to tell is to shoot both of them with same exact powder/bullet/OAL combo, but switch primers. I like to keep the same cases and keep them shot the same number of times. I also like to weigh each individual powder charge. I have been loading my last couple rifles pretty much right at the lands. I have done this with 4 of the bullet in my 7 mag, and my extreme spreads are no more then 15fps. Thats pretty good if you ask me. With the 162g amax, the diference between high and low is only 5-6fps.

 

[DougMH]

Is there really any way to have your most "accurate load" that doesn't also result in your least ES?

It's pretty much a law of physics that your vertical spread of rounds is going to be greater with an ES of 80 than it will be if your ES is 20. But it also has to do with the distribution of that ES.

Also, ES must be coupled with SD. You could have 19/20 rounds with an MV of exactly 2,750 fps and if round 20 of 20 is 2,670, you've got an ES of 80. Round 20 of 20 could have been off for a number of reasons. In that scenario, I whould be ecstatic. I would just discard case 20 of 20 and go shoot a match.

If you're going to win matches at 1,000 yards, you've got to come as close as you can to and SD of <= 6 and an ES of 20... on a consistent basis.

And we're only talking the vertical here. You also have to learn to read the wind. In my last 1,000 yd match 17 of 20 rounds would have been 10's vertically. Shooting in the 3rd relay and not being an expert (not even good) at reading the wind, I finished about mid-way down the list.

So, how do I get my vertical minimized?

1) Meticulous case preparation (details if anyone is interested)
2) Powder measure accurate to .02 grains (GemPro 250 and/or AccuLab 123)
3) Bullet runout to +/- .002 on the dial indicator (Hornady guage).
4) Lapua brass
5) Berger bullets (on the lands)

I shoot .308 F/TR using a 185 grain Berger BTHP

 

[Scot E]

Out to 5-600 yards this doesn't make as much difference with most hunting cartridges. But for over that I use this list.

1. Temperature stable powder with charge filling 95% to slightly compressed, weighed to .2 of a grain. If shooting over 1000 yards keep them within .1 of a grain.

2. Bullets- sort by bearing surface to .002 then by weight to .2 of a grain. If shooting over 1000 yards I cut both numbers by half.

3. Micro seating die to seat the bullets exactly the same distance from the bearing surface to the lands.

4. Bullet run-out .001

5. Don't mix new brass and once-fired brass.


Scot E.

 

[rscott5028]

Top three things to reduce ES and SD...
(1) consistency, (2) consistency, and (3) consistency
...for everything from components to shooting technique.