I have few Vietnam-era 20-round mags that feed Ok but sometimes fail to lock the bolt back. I'm pretty sure the springs are weak. I also have a bunch of brand new springs for GI 30-rounders. Can I trim these springs and use them in 20-rounders? If yes, how many coils need to be cut off? I realize that I can count the coils in both and calculate the difference or have my 6-year old do it, but is it that straithforward?

Order new from Brownells when back in stock.