Where to start:
1. A shotgun shoots 100% high. All the guns in that model line shoot 100% high. Okay, it's a trap gun.
Another brand or model shotgun shoots 110% high and 4 inches to the left. But nine out of ten of the same brand and model shoot 60/40 and to aim. That is NOT a matter of gun fit! 1/10 is wrong, or 9/10 are wrong. That's a manufacturing error. You find out on paper.
2. Get you some steel shot, some tungsten shot, and some lead. Shoot three patterns, don't change your choke. Get ready to be GOBSMACKED at the differences.
3. "Looking at patterns." If you don't know how to "look", you won't understand what you "see". If you have not had at least a semester of statistics, or put the effort in to really study statistics, with all love... you are like my wife looking in the gun store for shotguns. She doesn't know a side by side from a bolt action goose gun. Therefore, all shotguns are the same. I don't pattern looking for density patterns, because I know statistics. But I know that there is stuff I could do to ruin a pattern... cheap, soft, non-uniform shot, drive the stuff at 1600 fps... stuff like that.
4. Do you know what your "modified" choke looks like?
If shotgun bores were straight pipes... the better barrels have several transition zones inside the bore, not at all like pipes... so what is the bore diameter?
If all shotguns had the same diameter... aside from all 12 gauges not having the same pipe diameter.. you have all the different gauges, too
If all chokes were simple linear constrictions... some have a hyperbolic-y profile, some have an abrupt step, how do you know what your 12 gauge 5/10 Fabarm choke patterns like from a tribore barrel if you don't pattern? (Answer.. it's a very tight Mod, maybe even IM depending on ammo) without shooting paper? Note, my 20 gauge 5/10 thows a more open pattern than the 12. Huh. How do I know?
5. Once you know something about your gun and how it shoots... yes.. you need to work on fit and even more, your hold and stance.
Noweil and I shot some trap last weekend... and I finally got dialed in on my hold and stance. Lightbulb goes on. BING! Okay! Now I am hitting clay. It took about half a box to get it. Then we shot skeet and with my new stance (more forward lean, crawling the stock) I had about as good a score as back in the day when I was shooting in a league.
But if my shotgun was not shooting right, if I didn't have a clue as to which choke to use or what they did, and I had not been working on things for years... that would not have happened. Yes, shooting at flying targets is very important. But so is making sure that your shotgun isn't borked. Especially if you shoot more than one gun.
6. STOP with the shot string nonsense. Science works. The target is going 40 miles per hour or 59 feet per second. The shot is going about 800 feet per second and has a "length" of 10 feet. 10 feet x 1 second/800 feet = 0.0125 seconds from when the first pellet hits to the last.
At 59 feet per second, the target moves 59 x .0125= 0.73 feet or 8.85 inches.
This assumes the target is crossing exactly at 90 degrees. Any slant, and trigonometry says the variation is less.
This assumes the lead is evenly spread out in the string. IT ISN'T. Most of it is in a ball, with some leaders and some laggers. That means the variation will also be a lot less.