Corbon 220gr Sub-sonic Velocity & Accuracy

[John3]

I am newto this forum, and just got a new SSK .300 Whisper M16 upper, w/10" barrel and suppressor.

Corbon 220gr sub-sonic is chronographing at 1035fps, high 1050, low 1020, with an SD of 10 fps. Corbon claims 1040 fps, so my results are very close.

This is outstanding considering how small these powder charges are.

This level of velocity variation should add only about 1/2" of error at 100 yards (according to my Oehler Ballistic Explorer Program).

I am not happy with the grouping, however.

I'm getting 4"h x 2"w groups, using a Leupold 20x scope.

The high shots are not related to high mv's, and the low shots are not related to the lower mv's.

Anyone have any thoughts?