I have an M&A 16 inch flattop HBAR kit on a Bushmaster lower and a Rock River Arms tactical carry handle with A2 sights. When shooting at different distances, 50, 100, 200 and 300 meters my groups all look the same. centered on the target horizontally but scattered vertically across the target. At 50 meters the groups form a single vertical line about 4 inches long in the middle of the target, at 100 meters it looks about the same except about 6-8 inches long, 200 meters is the same but about a foot long vertical spread. At 300 meters I am lucky to hit the target, however the rounds that do hit are normally centered but scattered up and down the target. I am thinking it is either the hammer spring is way too strong and causing movement upon release or I am making some kind of mistake in my manipulation of the trigger. Any opinions would be appreciated.

prone unsupported

I tried several times shooting over the cab of my truck while sitting on the side of the bed using a balled up blanket for support. does the same thing.

This is what happens when You rest on the Mag, Get a bipod or a blanket/Mat (As was suggested) and Try it again. Keep it off the mag while shooting, otherwise it's like "Teacupping" while shooting a pistol.

Good shooting!,
Tall Shadow

I agree that it is your breating...  shoot on the natural pause after you exhale naturally.  dont blow the air out.