Not trying to be mean or pick a fight! I was genuinely curious as to rather or not you were making a joke. Assuming you're being serious and not just trying to "troll" folks like myself, my objections to the practice you were endorsing are as follows:
1. Point of Impact Shift: Different barrels and rifling patterns perform better with different bullet types, powders and overall lengths. While it might be a small difference going from 115 grain in one hollow point design with one powder to another, you are tolerance stacking by running multiple brands, bullet weights and configurations. This is maximizing your group spread from a mechanical accuracy point of view. That is irrespective of the shooter. You can lock the gun in a rest and see this effect.
Generally speaking, and this is very broad and weapon/shooter dependent, less recoil lowers POI, more recoil raises POI, within a given given bullet weight. Since bullet weight impacts recoil and slide energy, changing bullet weights from shot to shot exacerbates the effect. POI shift is also velocity dependent, so adding different burn rates of various powders with different bullet weights means you will be as inaccurate as mechanically possible in a given firearm.
2. Training: Irrespective of accuracy, changing the bullet weights and powders inside the magazine will result in every shot feeling different from the last. Consistent feedback is an important part of the muscle memory utilized in recoil control and learning how to drive a gun quickly from shot to shot and target to target. If your recoil impulse changes dramatically from shot to shot, you are making it more difficult to bring the gun back on target as quickly as possible in a given string. Its very difficult to find a shooting rhythm and ride the recoil if the recoil of the gun changes every shot.
3. Malfunction Inducement: By running your guns slide at different speeds and with different bullet shapes and different OAL in bullets, you are maximizing the situation where even a reliable handgun can choke up in feeding. Remember the shooter will also be giving different feedback to the gun with your grip via each shots recoil being different.
4. Gun Wu Wu: This last one is pretty unscientific, but I think most people who have shot one gun a lot will know where I am coming from. When you get used to one load and one firearm, you can "listen to the gun talk" during strings of fire. You don't need to see that you have fired your last shot, you feel the slide lock open. You know its getting time to clean it when the gun "tells" you its getting crunchy. You know immediately if you had a squib or some other issue because that shot felt different that the thousand or so before it. I know not everyone carries the same gun on duty day in and day out, or shoots tens of thousands of rounds a year in competition, but I don't know why you would rob yourself of the change to learn your guns "feel" by making it feel different every shot.
