Right now, the trend in the ammo world is to go to lead-free frangible ammo that disintigrates on contact with something harder than itself. (www.ttiarmory.com, www.frangiblebullets.com) The lead-free movement was started due to lead poisoning issues among police recruits, police officers during training, and private shooting range employees. The use of lead-free ammo is also being pushed by the EPA-types due to the huge cleanup costs associated with lead contamination from bullets laying around shooting ranges, especially outdoor ranges like on military bases.(
http://www.capecodonline.com/base/bullets.htm)
The lead-free ammo uses metals other than lead, but these metals have different properties from lead that cause them to disintigrate on impact. See www.pmcgreen.com for one example. Using non-disintegrating material other than lead may also run into the "armor piercing bullets" problem. Steel bullets are banned because of this issue.
Right now in CA, there is a competing bill to ban all leaded ammo due to concerns over lead poisoning among the California condor population.
http://leginfo.ca.gov/cgi-bin/postquery If this coding bill bill passes, its implementation will conflict with the lead-free ammo bill.