Muscle Memory is an Un-conscience Reaction. Yes a bad term as mentioned, muscles are meat and have no memory. But it has to be called something so someone picked that term. I don't know who, I've heard it all my shooting life and when said, most everyone in the shooting community knows what it means.
Whether we want to accept it, un-conscience reaction, or muscle memory (which I'll continue to use) does exist.
Its an reaction, same as if someone slaps toward your face. You flinch. You don't consciously flinch but you flinch just the same.
Like the guy who had a rattler in a fish tank, you paid your quarter and if you could keep your hand on the glass while the snake struck, you won ten bucks. No one could, even though they knew the snake couldn't strike through the class, you moved because you are conditioned to dodge danger, even though you may have never been bitten by a snake.
We could say its a habit, which it is. Like slapping the trigger vs. squeezing the trigger. If you practice slapping the trigger you're going to slap the trigger without thinking about it when you shoot. Whereas if you practice squeezing the trigger, you're going to squeeze the trigger without thinking.
That would be habits, or as many call it muscle memory. If you go to a steel match where time is involved, you're not going to concentrate on squeezing the trigger every shot, if you did, you'd run out of time and end up the at the bottom of the score board.
That's why we dry fire, concentrating on squeezing the trigger to develop a habit or muscle memory or un-conscience action, what ever you decide to call it.
This occurs in all fundamentals of marksmanship. Lets take breathing. We don't concentrate on our breathing, we just do it as we trained or practiced.
I was shooting the Setting Rapid Fire stage at the Wilson Matches, (National Guard Championships) one year. You have 60 seconds to get into position, shoot two rounds, reload and shoot 8 more at 200 yards. I normally shoot the stage in about 45 seconds.
My scorer watched me shoot then asked about my breathing, "how can you breath and shoot that fast". I didn't know, I knew I breathed but I didn't know how. So the next string I tried to concentrate on breathing to see for my self, it was the worse 200 yard RF sting I shot in my life.
Another example, some people regardless of anything else, never look over a rifle without looking over the sights. That is something my father drilled into me since I could remember. Fast forward to my Senior Trip to SE Asia, many times I'd empty a magazine and noticed I was still looking through the sights while reloading. It was a habit I obtained a long time ago, and I still do it to day while hunting or in competition. I always look at the front sight. Never knew any different.
Some times you have to think, I have that problem when coaching. I often neglect the front sight lesson, WHY, be cause I cant imagine looking over the barrel of a gun (handgun or rifle) without looking at the front sight.
You often see the term "driving a rifle". I always thought that was stupid. You drive trucks, not rifles. That is until Jason of Rifles Only explained it. Shooting is like driving. When you're driving down the road you don't think but your hand is constantly moving the steering wheel. You're guiding the truck or car down the road un-consciously, you don't tell your hand to move the wheel this way or that, you just do it. Without thinking.
It is no different than shooting, or should I say it should be no different in shooting. You train, you practice, and eventually you're driving the gun.
This is critical in self defense. If you had to think and deliberately tell your hand to move, draw, point, look at the sights, put your finger in the on the trigger, squeeze, etc. etc. You're going to be in trouble.
It takes hours upon hours, days upon days, on and on, of practice to drive the gun without thinking. Because when something happens, you can't think, you're scarred poop-less. You freeze.
As to switching guns. I've done it, I get on the wrong safety a time or two, sure you can catch your self and realize your carrying a 1911 instead of a 92FS, but you loose a second or two, which could move you several places down on the crying board in a steel match.
But what happens in a threat situation. You're in trouble if you cant get your first shot off in under a second. You don't have time to fumble with the safety because you have the wrong gun. In this case you more then likely will freeze. I've seen it in police work and I've seen it in combat.
You can believe this or not. Before you make up your mind go to a shooting class or match and watch people fumble, and watch others react without thinking.
Muscle memory is real, even if misnamed. You can train your self or you can hope. The choice is yours.