I came back to this thread, as I have a suggestion that I have not seen, so far. And Toughshed, you should consider this, also, based on your comment.
I have had inconsistent killing seasons for the last 10 seasons. Sometimes I would kill everything I hit, and other times I would just wound the birds. Irritated the heck out of me to wound birds, instead of a clean kill.
So, for 10 seasons (I started pheasant hunting in 1970, or so, but didn't have a Colorado area until 10 years ago) I just kept beating myself up about how bad of a shot I could be, while other days it was 3 shots, 3 in the bag. I did trap and sporting clays, but still, varying results.
For the last two years I had been paying very close attention to how my gun was mounted after each shot. Bottom line, it was not consistent. I paid very close attention to the mount with most shots, but it was still inconsistent. So much for muscle memory.
So, Friday I went to a gun fitter, and had my gun fitted to me. He sanded off some of the stock by my cheek, cut 5/8" off the stock, and also sanded the stock so the butt plate hit my shoulder on the same plane as my shoulder (previously, only the inside edge of the butt plate was hitting my shoulder).
I went out yesterday, and dropped (and bagged) all three birds I shot at, two of them dead when they hit the ground. This has not happened yet, this year, and I have hunted at least one day every weekend, sometimes 3 days in a row. So, while I know it could have been perfect alignment of the planets, I have to think the gun fitting made a big difference.
So, my 2-cents towards consistent shooting is to get your gun fitted to you. It was pricey, much more than I anticipated ($350), and I may have been "taken", but my mounts are the same each time, now, even in my living room. I am looking down the rib every time I mount the gun, instead of off to the left, off to the right, high, low, or sometimes, even down the rib.
Getting a misbehaving gun fitted to you is cheaper than a new gun, and I know many of us think a new gun will make us shoot better. I have 4 guns that prove that theory doesn't work. Hope my fitting keeps working. Still have three more weekends to find out this season!