For those who think a rifle barrel's resonant frequency significantly changes enough to be noticed with different forces applied to it as well as its temperature in a range where humans survive, please contact Tom Irvine at:
...about his website:
...then tell him to fix his software in the above web site that's named below:
"Natural frequency of a rifle barrel with free-free boundary conditions."
so it will match your theories of how such things will happen.
Then be ready to explain why his software is wrong.
Also, contact the American Society of Mechanical Engineers and have them suscribe to your theories because if Tom Irvine's wrong, there's got to be hundreds (thousands?) of engineers working with vibration issues that are also wrong.