Small groups- Large SD ?

[Jtate]

I am working up loads for a new rifle. 243 win, 87 grain V max, H 4350, Wolf primers, Hornady brass. Group size at a 100 yards, 2 to 3 tenths. ( three shot groups ) but the SD is at 27 fps, what gives, why does this happen?

 

[Ned Ludd]

At 100 yd, that kind of velocity may simply not be sufficient to have a large impact on group size...but it will definitely have an effect at 1000 yd. Optimizing powder type/brand and charge weight, as well as consistency in neck tension are a couple ways you might get that value down. Sometimes using a different brand of primer can also help lower ES/SD. Unfortunately, you ideally would like both low ES/SD and small group spread. Sometimes trying several different things (although not all once in the same loaded round) can be the only way to obtain both. Another thing to check is whether the effect is largely caused by a single outlier within the group. If so, you can closely inspect that piece of brass (weight, volume, neck, etc.) to see if you might find something abnormal that could help account for the velocity deviation.

 

[dmoran]

100yd target folktales don't always tell the same stories down range - IME
Donovan

 

[savagedasher]

If the group is .300 at 100 and all vertical It can be the 28 ' of sd Have you got the sd smaller ? Larry

 

[Jtate]

I think it is the brass, ie neck tension and case volume. Also something that I think I am seeing is: as the charge weight goes up the SD comes down. Best group is at 43.5 grains, with no sign of pressure, I will try to find next higher node