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SD how many rounds.

 
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  #8  
Old 05-09-2006, 04:27 AM
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Re: SD how many rounds.

I wonder how many people realize that if 3 ain't enough for standard deviation in muzzle velocity, then how in the heck can 1 per charge weight be enough for a ladder test used in developing optimum powder charge weight?
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  #9  
Old 05-09-2006, 04:38 AM
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Re: SD how many rounds.

Whenever I do a ladder test, once I find the "node", I then shoot 10-15 5 shot groups with that load to determine if I have truly found "the node".
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Old 05-09-2006, 08:23 AM
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Re: SD how many rounds.

[ QUOTE ]
Three shots will work to get an idea but then test the load again and again (on seperate days in differing weather conditions) in three shot groups to verify that it still works. If the sd goes up or down 1 or two feet per second over the course of the re-test, then it will work well for you.

[/ QUOTE ]

100% Agree [img]/ubbthreads/images/graemlins/smile.gif[/img]

One can get a lot more mileage out of many 3 shot strings than 1 10 shot string, IF you're LRH preping not BR preping.

By the time I have settled on a load that looks good, the first 3 shot ES and SD look good. The next 3 shot string zeros at a chosen distance. Then next several 3 shot string are for drop chart development out to as far as the rifle should reach.

By then you have the SD and ES of sufficient number of shots, drop chart is preped, you're ready to go "harvest" somethin' and you're barrel isn't warn out. Probably about 30 shots or so.
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Old 05-09-2006, 08:40 AM
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Re: SD how many rounds.

[ QUOTE ]
Whenever I do a ladder test, once I find the "node", I then shoot 10-15 5 shot groups with that load to determine if I have truly found "the node".

[/ QUOTE ]You'll have a more statistically realistic (correct) group if you shoot one 50-shot group than ten 5-shot ones.
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Old 05-10-2006, 04:11 AM
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Re: SD how many rounds.

Please explain.
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Old 05-10-2006, 07:32 AM
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Re: SD how many rounds.

[ QUOTE ]
Please explain. (regarding my comment: You'll have a more statistically realistic (correct) group if you shoot one 50-shot group than ten 5-shot ones.)

[/ QUOTE ]The center of a 50-shot group will not be at the same place as the centers of any one of ten 5-shot groups. That 50-shot group center more closely represents the center of all shots fired; past, present and future.

Arsenals calculate group center from several dozen shot holes for military ammo; some groups have 200 to 300 shots. Then they calculate the group center based on the average vertical and horizontal shot hole position. That plotted group center is then used to calculate the radius of each shot from group center then the get the mean radius for that ammo lot. Mean radius is probably the best way to determine accuracy, but it takes a bunch of ammo to do it with a high level of confidence that it's correct.
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Old 05-10-2006, 07:48 AM
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Re: SD how many rounds.

[ QUOTE ]
wonder how many people realize that if 3 ain't enough for standard deviation in muzzle velocity, then how in the heck can 1 per charge weight be enough for a ladder test used in developing optimum powder charge weight?



[/ QUOTE ]

Wonder how many people know that a ladder is not used to find the optimum charge weight? Quit thinking in terms of OCW. It is used to find the node and the extreme ends of the node, and then you fine tune for the final charge weight, seating depth and neck tension inside that node to get a final tuned load that beats anything else. Once inside that node, just a matter of series of groups with tweaks on powder, tension and depth. Basic common sense dictates repeaded groups to confirm.

BH
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