standard deviation for subsonic rounds

[RWBlue]

What is a good standard deviation for subsonic 300-221?

[320pf]

RWBlue,

I do not know what would be considered "good" Stdev. I think for small Stdev. with subsonic loads you have to weight each powder charge. Your best bet would be with an digital electronic scale.

My sub-sonic loads run like this:

165g Speer BT in front of 8.5 g AA#9: 1089 ± 6 fps
180g Sierra GK BT in front of 8.5 g AA#9: 1154 ± 54 fps
180g Sierra GK BT in front of 7.5 g AA#9: 1034 ± 52 fps

320pf

[RWBlue]

I guess I am not doing to bad, but I need to get up to speed.

240gr 900fps SD 32

[320pf]

RWBlue,

What powder are you using for this load

[RWBlue]

9gr W296 900fps 10.5 inch barrel CCI SRM primer


I will be trying to get close to the speed of sound on the next outing.
I am also switching to Russian primers because I am out of my CCI primers.

[Ranb]

Using WC820 (like H110) and Sierra 240 HPBT I get 19 fps stdev in my contender, 11 fps in the AR15. Using cast 225 grain I get 9 fps stdev in the contender. The fast burning powders are usually more consistent. I use standard primers; I did not get better results with magnum primers.

Ranb