Shooting from a rest.
The true test would be from a ransom rest if we could get S & W M & P grips.
The M&P does not require an unorthodox hold.
I completely agree. The M&P does not require an upgrade to shoot accurately. I know many who do just fine with the stock gun.
How you shoot a different gun is not definitive. It does let us know that you have at least the ability to shoot well. That doesn't mean you'll shoot well with every gun. I shoot my 1911 better than my M&P. That doesn't mean my M&P isn't accurate. It only means I don't shoot it as well as the 1911. From a rest, both guns are very accurate. The 1911 is better than the M&P, but that has nothing to do with how I shoot it.
The rest helps to eliminate the human factor. Shooting while standing introduces many gross errors. Whether the inaccuracies are you or the gun is unknown if you can't eliminate your influence.
Well, that should tell you something. Why can you shoot his OK, but not yours? At first blush you might think it's your gun. Well, obviously you already think that. It certainly is a possibility. Alas, until you shoot it from a rest, you don't know that's true. A difference in triggers would account for your issues.
What always amazes me in circumstances like this, is how hard people resist shooting from a rest. Why not just do it?
The true test would be from a ransom rest if we could get S & W M & P grips.