Are shorter barrels more accurate?

[noone]

I have found that if I eliminate all play between upper and lower receiver, I get better accuracy, so that is what I do.

Of course, the military has far looser requirements for accuracy than I do. The military's willingness to accept play between upper and lower receiver may mean that the rifle's accuracy still falls within acceptable limits. And that is fine for them.

To each their own, but for me, I get better results when I eliminate play between upper and lower, so that is what I will continue to do. Your mileage may vary.