I have never fired a modern automatic weapon, but I have fired a Mauser machine pistol. This was about 50 years ago when I could still see what I was shooting at.

The first thing I figured out was that if the target was more than four feet away there was almost no way I was going to hit it. Think of holding a full sized jack-hammer with one hand and trying to carve a block of marble.

So then I used the add-on shoulder stock. Not much better, but now my shoulder and my wrist were sore.

I am sure that using both hands to hold the weapon would increase the accuracy, but that was not an option with the Mauser due to the fact I feared blowing my left hand off.

So I can see where if you were shooting from any distance at all it would be tough to have a tight grouping.