Springs for pre-ban 20-round mags

[Alex9661]

I have few Vietnam-era 20-rounders that could benefit from new springs, they feed good but sometimes fail to lock bolt back. I have a bunch of brand new replacement springs for 30-rounders. Can I trim them and use in 20-rounders? If yes, how many coils need to be cut off? I can always have my 6-year old count the coils and calculate the difference , but I'm not sure it's that straithforward.

 

[DrNVP]

Wolff springs.

gunsprings.com

 

[Alex9661]

Wolff springs.

gunsprings.com

I know, I'm a cheap bastard