1st shot of my 1" groups thrown everytime

[crowminator]

Hey everyone,
I have an AAC 7.62SD suppressor mounted on my M1S upper in 300/221 Fireball. Everytime I shoot subsonics the first round consistantly lands 5 inches low and 5.5 inches to the left. I can shoot the same bullets supersonic and this does not happen, with or without the suppressor.I am shooting sierra 180 grain bullets in a 1" six shot group at 100yds not counting the flyer. Today I tried some grease in the blast chamber and got the same results with the first shot being a flyer. I have fired several hundred 110gr and 125 gr supersonic bullets with the suppressor attatched with no problems. Has anyone ever seen this before?