Sorry, no, I've never seen one -- that I was ever aware of.

So I have no idea what it looks like...

In 99.9999999999% of American usage, a "spring" is a coiled metal object.

If this sort of "spring" is exclusive to guns and gunsmithing, I've learned something.

Is a "leaf spring" a common gunsmithing term -- and is that what this part technically is in gunsmithing terms?