ARES M60E4 Spring.
 

I have an ARES M60 and i had pulled the spring out because it was noticibly weak (Couldn't pierce cardboard or a can) So i wanted to upgrade the spring. I had the original spring from my DBOYS AKS74U. The spring was at leas an inch and 3/4 shorter then the one installed in the M60. I've been searching all day, even read the owners manual and nothing said anything about the spring. Any help would be appreciated.

It technically will take any AEG spring so your spare should be fine.