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SD and ES number

 
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Old 04-11-2010, 10:54 PM
mo mo is offline
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Join Date: Mar 2006
Location: mississippi
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SD and ES number

Iworked up a load for my 6.5x47 lupua this weekend, and found a couple that might work well. Three of the groups I shot were an inch at 300 yards. I chose 42.5 gr of h4350 with a 130vld. Average muzzle vel. is 2947 fps. ES is 21 SD was 8 I think that's fair, but what would be the first thing some you would do to lower the SD and ES numbers. I tried different neck bushing, but sense the 4350 is a compressed load it just pushed the bullet out. SO HOW CAN i GET THOSE NUMBERS LOWER?????
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Old 04-11-2010, 11:36 PM
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Join Date: Feb 2008
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Re: SD and ES number

I've been focusing on consistency in every aspect of the load. Everything from case prep to primer seating pressure. Also keeping a much closer eye on concentricity seems to be helping. I actually shot a load last week that was only three shots but had an ES of 1.
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Old 04-12-2010, 02:20 PM
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Join Date: May 2008
Location: South of Canada and North of Wyoming
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Re: SD and ES number

Like Moman said, the main thing for consistant results is consistancy in prep. Some load combinations, powder, primers, brass and bullets just may not give the best results.

Having siad that, I focus more on actual results (read bullets holes in paper or on steel) than what my chrony may or may not be telling me. If you shoot two chronys back to back, I'm guessing you loose confidence in the level of accurate reliable info it is providing you. Another thing is that ES and SD are statistical measurements and calculations and as such, need a good population size to provide any meaningful information. From a 3 shot group, SD means nothing and ES means next to nothing. For any meaningful ES, you should have at least a 5 shot group. For a meaningful SD, you should have a 10 shot group. Before you get too carried away with SD, you should look it up and find out exactly what it is and how it is used, if you haven't already. The next thing to consider is repeatability. If your data and results are not repeatable, they mean nothing. So, what you should do, is fire a 10 shot group on a particular day, record the results and then fire another 10 shot group on another day and compare. You might be in for a big surprize. While you're doing this, shoot for groups at various ranges out to the distance you want to be able to shoot. Bullet holes are more meaningful then chrony data. and just because you get a low ES and SD doesn't at all mean you have an accurate load.

Good shooting,

Mark
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