An old thread but a timeless issue. Almost all handguns are known to shoot higher or lower depending on the weight and velocity of the bullet being fired. A faster/lighter bullet spends less time in the barrel, so there's less time for the muzzle to rise before the bullet gets out and is no longer affected by where the barrel is pointing, and results in a lower POI.

If the way a gun is gripped will also produce side to side torque as well as muzzle rise after ignition, the same principle will apply to the bullet's windage as to elevation. Hence the advice - fiddle with ammunition first, before fiddling with the machinery.