Dry fire. It can be boring, but its one of the best drills you can do to help build up muscle memory. Its also very cost effective. When you go to the range, dry fire 3-5 times then fire one round. Repeat that several times as a warm up. You can also get into a good firing position with an empty chamber and have someone balance a coin on the top of the barrel near the muzzle, then pull the trigger. You should be able to pull the trigger without any interruptions to the coin. You can use other objects as well (spent pistol shell casings balance vertically, washers, etc.). You can always throw a snap cap in the chamber if you don't like dropping the firing pin on an empty chamber.
Good trigger control combined with a good natural point of aim and good firing position will yield solid results every time, regardless of what you are shooting. The consistent horizontal shifting in your groups show that you are either pulling the trigger to side during the pull or you are trying to push/pull the rifle onto target and hold it there, thus making a consistent point of aim difficult to maintain. Someone already covered how too establish a natural point of aim, that is important when trying to maintain small groups.
Another thing to check is your eye relief and parallax. If your scope isn't mounted correctly, you can get scope shadow which will influence your grouping size and POA to POI. Also, if you are turkey necking every time you fire trying to get a good cheek weld, your scope may be mounted to far in either direction. Keep in mind that at increased magnification, the more sensitive your scope is to scope shadow. You can try backing off your magnification a few notches and see if your group improves. Poorly set parallax will also influence your group size slightly as well.
Once you start shaking things out, and build that muscle memory, you'll start to be able to feel when things are out of whack and thus able to "call your shot" and know what went wrong with wide groups or random fliers. It appears that your groupings aren't terrible, so it may be something small or a combination of small things that you are doing. I know it can be frustrating especially when you are firing rifles and ammo you know are capable of better performance. If multiple firearms are doing the same thing, then its probably something you are doing during the firing sequence.
