Velocity Deviation Problems

[pcso112]

Having some problems with my velocity deviation with 220 and 240 SMK’s. After doing some reading I understand that this is not a unique problem for the larger subsonics. My horizontal groupings are sub-moa, but my vertical groups are as large as 2.5 moa and I am seeing 80+ fps deviation in my velocities. Painstaking care has been taken to insure that all my cartridges are perfectly uniform.

I am using a 21-inch Hart barrel with 1 in 8 twist on a Remington 700 action. My suppressor is a YHM 762 Phantom. I have been loading up cut down 5.56 06 LC brass. I use CCI BR2 primers and have had the same velocity deviations with both H110 and Reloader 7.

It also appears that the 240gr SMK’s are not stabilizing and aren’t flying straight. It is apparent on my targets that about half are landing off center.

I am headed to town this weekend and will be picking up a different powder. My question is, can anyone tell me is there a particular powder that might be better suited toward my 21 inch barrel for subsonics?