A couple of week ago I e mailed metal tech with the same question cause I am lookin into making a feild anyways this is the e mail and response.
Sent: Friday, March 16, 2007 3:19 PM
Subject: Just one question
What are the bbs made of? I lied 2 questions is it
There are actually no true Bio-degradable bb's currently sold in North
America. To see what I means check this post on Arnies Airsoft. The
Bio-Val are but they are nearly impossible to get hold of. We are
looking into it but they will likely run about $30 to $35 / bag.
Phone: 1 866 979 2774 ext 300
So if we are all interested in bio bbs we should all e mail him and let them know that we will pay the extra for bbs. I dont care how much plactic is in it that aint good to litter that everywhere. Also some birds(I not a bleeding heart) have been eating them and dieing I have read. So there are side effects from what I read.