So a bullet pushed into or against the rifling before firing will cause a gun to blow up? So thousands of competive shooters with other rifles have their barrels chambered and/or the bullets set out to do just that. (A long leade will allow the bullet to skid when it takes the rifling, affecting accuracy.)

But the AR-15 is different? What works for other rifles causes an AR-15 to blow up in a mushroom cloud?

At the pressures involved, a normal bullet acts like silly putty; it will move into the rifling with no problem. The only thing that can raise pressures would be too tight a chamber neck that would not allow the bullet to release properly. And that should not differ between commercial and military ammo.

I think some "experts" are off the track.

Jim