AR 15 10 round spring length?

[TZCHRIS]

OK, so I had no luck finding 10 round mag springs for my AR 15. I bought some 30 round springs and will have to cut them down. Does anyone know the spring length of a 10 round mag? I guess I could start long and experiment but that seems like it will be a PITA. Would like to get a good starting length and I can adjust from there.
Thanks, Chris

 

[transamkid86]

Whwn I took apart my mags and I put the springs back in they stuck out about and inch from the bottom before u have to stick it in there to put baseplate on...so I think that would be a good cutting point?