Hmm. This is one of those questions that has an infinite number of answers depending on the particulars.
But I will chime in and vote with the "proper load development" as the cause. I think a lot of people just go out and try the wrong combination from the get-go.
Even seasoned experts have to go through this with a new gun. I would never expect anyone to know the right load without experimenting first.
As far as #1 accuracy problem, as in the shooter is perplexed as to why he's getting unsatisfactory accuracy - either poor technique, or cleaning.
And a couple comments on the sqabble over the "efficiency". I would like to clarify that Sam Fadala does not promote the "most accurate" load as the optimum. In his books, he defines the optimum as a balance between accuracy and power. So, I believe Mr. Fadala would choose a more potent load over the most accurate load if the more potent load was "accurate enough".
When hunting, I would rather blow a 3" wound channel taking out 1/2 of the heart and a good part of the lungs, than poke a mere 1/2" hole plumb center on the heart.
When target shooting though, I would rather blow a 1/2 inch hole in the X-ring than put a 1/2 hole in the 8 ring and make lots of dust fly on the berm.
Sam's discussion of the PODR is simply to define it as the point where you start to get less velocity gains and less accuracy for the amount of powder added and more smoke and recoil. Optimum loads are defined as the best load for the purpose of the gun. A target gun's optimum load will be the most accurate. A hunting gun's optimum load will be a balance of accuracy and power. In either gun, the PODR may or may not be exceeded.
The most efficient load may or may not be very accurate. The most efficient load may or may not be "powerfull enough".
A load that is the most accurate, most powerful, AND the most efficient is probably very rare indeed. When hunting, I'll sacrifice a little accuracy to gain some extra power, and I'll sacrifice a lot of efficiency. When competing on paper targets I'll take as much accuracy as I can get at the expense of power and efficiency. And while plinking, I'll go for an efficient load.
