Originally Posted by Lancet
Wld be my S.D? It holds a sub zero group at 100 yards, ii can make all 3 in a group touch with it.
S.D. stands for Standard Deviation, which is the average difference between muzzle velocity from shot to shot Example; 5 shot group shot 1 3125 fps
shot 2 3250 fps
shot 3 3200 fps
shot 4 3175 fps
shot 5 3165 fps
This would be an example of a load that has a large extreme spread 125 fps the s. d. on this load would be somewhere around 25 to 28 fps.
An example of good S.D. would be shot 1 3200 fps
shot 2 3220 fps
shot 3 3210 fps
shot 4 3218 fps
shot 5 3207 fps
In this example the extreme spread is only 20 fps which would give you a S.D. (or avaerage) of around 5 fps.
What this means is your load is tuned and it is going to be much more consistent, I always try to find a load that has an S.D. in the single digits(9 or less)
When shooting out past 500 yards this will make a differnce, your groups will be better, I would take a load with a low S.D. that shot a 5/8" group at a 100 yards over a load that shot a 1/4" group at a 100 yards with a high S.D.
Hopes this helps I am not good at putting Sh-- on paper there are others on here that could explain it better if you would like more info you can pm me and I can give you my phone #