I see. Another related question is that collision boxes seem to be somewhat "penetrable" if enough force is applied between objects or collision speed is high..don't know. In my video here I made a ring off overlapping collisionboxes inside the rings and still I manage to "break" the chain by hitting it with a barrel hard enough. Is there a way to make the collision boxes "less penetrable" ?
Unfortunately, that's a pretty common phenomenon in collision simulation. If enough force is applied, any given body's newly acquired velocity might sometimes be enough to push it to the opposing side of an obstacle. The most thorough solution is to to increase the frequency of the calculations, but that's something that would have to be done on the engine and would come with a performance cost.
For you, the best options are to either make the chain's links thicker (collision mesh, not necessarily the visual model), or take the smoke-and-mirrors approach and just use hinge constraints to connect the links (less physically accurate, but you get more control over chain breakage, it's potentially infinitely stronger, and you save on some physics calculations).
