I bet you could solder the springs together top to bottom and it would work. That way it doesn't get too hot and lose it's temper... The pic of the joint is terrible, just enlarged. Doesn't show much.

I was going to do something similar with some Remington 760 mags and make a 20 rd mag...out of steel. Just cut off tops and bottoms like this one and spot them together with wire feed. Use an M14icon mag spring...