I have attempted to create a blueprint for a modular weapon. The stock, barrel, scope, silencer, etc is all attached to the gun in a Blueprint Class. When I spawn the item in the world or drop it from inventory the attachments swing around the base of the gun and bounce around even when not being touched.
To stop this I can turn off physics when it is spawned in and the gun won’t drop to the ground, but, when I pick it up and drop it my blueprint makes it go from physics disabled to enabled so the gun will fall to the ground. It then starts this behavior again.
Your problem is likely that you have multiple physics objects, where you only need a simple physics enabled collision box (simulate only after dropping), and a number of mesh components.
I created a collision box that covers all of the possible attachments. The attachments do not fly around randomly anymore. They go to that one position once dropped and stay there. I am looking to see if I can reset the position once dropped to have it look normal once more. Here is an example of what it is doing now.