Wolff Ext. Mag Spring - How much to cut off?

[marklbucla]

I've got a Wolff Magazine spring for my 870/1100s, but it's way too long. How much should be clipped off of this particular spring so that it works with a +2 tube and how much for a +3 tube?

 

[Onmilo]

Easiest way to figure this out is to install the extension tube on the magazine tube and lay the spring below so that it is flush with the receiver/mag tube interface.
Mark the point where the excess spring extends past the end of the extension tube and cut it of at that point