Is the Mk1 return spring the same as the outer Mk2 return spring and the only difference is they added a smaller second inner spring on the Mk2?

I was assembling my Mk1 buttstock and a dual Mk2 spring set fits no problem and it seems a bit stiffer than the single Mk1 spring (which seems like a good thing). Any issues using a Mk2 spring set in a Mk1 buttstock?

Thanks
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