I have finally got a decent combination for 600 yds, My vertical spread from my last trip with very mild crosswinds.. 1-5mph. is .3MOA, but my horizontal spread is 1.1 MOA. I realize the wind is likely a bigger culprit, but I noticed my sight picture moving horizontally with my heartbeat... How do I stop this??

Right now, I use a heavy front bag, and a squeeze bag on the rear shooting seated. I pull the stock in fairly tight with one hand. The other hand doesn't touch the stock.

Thanks in advance..