Model 12 part - what does it do?

[Three Foot Johnson]

There's a flat spring in the barrel band that doesn't seem to serve any purpose... what is it and what does it do?

 

I just bought a solid but "cosmetically challenged" Model 12, but all that seems to be wrong/missing/broken is this spring is missing.

[Boggus Deal]

It’s two main purposes is to keep tension in the mag tube to keep it from rattling and to keep it turned tightly into the receiver extension.

[Three Foot Johnson]

I came across this on another site:

 

When you take down a Model 12, the slide handle retaining spring serves to keep (retain) the wood forend (slide handle) in the forward position so you can store the barrel assembly without the slide bar all a flopping back and forth. Take down shotguns were a big thing in 1912.