I don't know if it will help but I found that shooting a double off the bench throws rounds all over, I was shooting a kodiak 45-70 double. I have changed to either a rest that keeps me sitting upright with my back straight or using a standing rest and the gun resting on my hand rather than on the bag. I have had the best luck with a tripod set of sturdy sticks works best for me.
That works for me others may not have the same results.
I am getting ready to regulate my 12 bore so we will see if I know what I am talking about pretty soon
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