Essential difference between a coil and other types of spring is that coils can only work with either external or internal guides. It happens that the guides also act as traps which hold together the bits of the spring in the event of a breakage and thus a coil will continue to function even if broken at one or more places.

The famed Russian vostok target gun uses bow springs, and I have seen two breakages in them. However, I am seriously willing to admit to being a V and flat spring jinx. No sarcasm intended.

Ah and the Dickson is my candidate for the best double ever built. A non ejector side pedal Dickson in 16 gauge must be the prettiest gun ever.