[Picher]

Subsonic bullets are affected vertically by air friction against the rifling marks to a much greater extent than supersonic bullets, which have a shock wave that minimizes air flow along the parallel body of the bullet and the "fins" created from rifling.

Exception: Bullets, like barely supersonic .22LR high speed bullets that, as they slow down between muzzle and target, pass through the supersonic>subsonic transition zone, which causes them to deflect horizontally about 1/3 more than bullets that either stay supersonic, or start as subsonic rounds.