Over the last 30 years or so, I have had a lot of different mechanical engineers that I have helped. I am an electrical engineer, and we don't get super bright MEs in electronics, because there are no moving parts, but we get a lot of MEs and we deal with shock and vibration.
The big problems with vibration are falling apart and breaking apart.
At a couple of companies, I will dig this book out of the ME's book shelf and explain it to them:
There are lots of applications with high vibration that will not shake loose, and there are lots of applications that will.
When I take a Rem700 barrel off, and find all that goop that the Remington factory left there, I know my calculations say it could shake loose, and they must have had a problem, but darned if I have ever been able to get a Rem700 barrel to shake loose. Vaughn offers a design change to fix this in the Rem700:
Guns have lots of screws and pins.
The only thing that I have seen again and again and again that came loose are the screws that attach the scope mount to the receiver.
An indicator is two holes touching on the target, followed by two holes touching way over there on the target.
I am not sure why those screws are coming loose.
I have calculated how much torque that scope mount screws should have.
I have tested the yield point of similar steel that is not part of the gun, and my calculations are right on for the various lubricants; 1) clean and dry, 2) oil or grease, and 3) wax.