Let's talk about what accuracy really means. I have almost 30 years working as a Metrologist. Accuracy is something I deal with every day.
First, we have to define what accuracy means, then we have to understand what it takes to be accurate:
ac·cu·ra·cy
[ak-yer-uh-see] noun, plural ac·cu·ra·cies.
the condition or quality of being true, correct, or exact;
That's simple enough, but there is another aspect we must look at; precision. In the case of shooting, this is the definition of precision:
pre·ci·sion
[pri-sizh-uhn] noun
mechanical or scientific exactness:
These two terms are not interchangeable. Look at this picture:
So, the goal is to be accurate and precise with our shooting.
The chart also introduces two new, but important terms; reproducibility and systemic error. Reproducibility is the ability of a person/machine to do the same thing over and over as it was done before. Systemic error is the error contained within the entire system.
If the shooter cannot repeat the same thing to get the shot, the shot will never be accurate and precise.
When talking about shooting, the shooter is part of the system. Believe it or not, humans can be extremely consistent in what they do. Thus, the example in the upper right, could be due to the gun or the shooter because both are part of the system.
This is why shooting from a rest is so important. By shooting from a rest error due to human movement is significantly reduced. It cannot be eliminated completely because ultimately it takes a human to operate the gun. Even if you use a vice or something like a Ransom Rest, the gun still has to be aimed and manipulated by the shooter.
So, to combat these issues we start to look at things we can control. Here is another chart that is very useful:
This is an example of how the shooter can affect the shot. Is it perfect? No. But it does give us things to look at to improve our shooting.
The gun is still part of the system and still has error. The M&P doesn't have a stated accuracy from the factory. But, if it shoots a 1.5" group, from a rest, at 25' (feet) I'll bet that S&W will say it's within specifications.