Your time line and story was correct up to the point about abandoning the tungsten bearing round due to the potential health and pollution problems were discovered.  We in the business called that the M855A1 (Version 1.0), and it was a very costly mistake based upon faulty research and data.  By the way all stocks of the tungsten bearing (Tungsten/Tin composite slug) Version 1.0 ammo was in fact destroyed and all the scrap sold off (but not as bullets or ammunition) at a significant loss or cost to the taxpayer. 

 Next came the M855A1 (Version 2.0) which was made with the same internal structure as the baseline M855 and the M855A1 (Ver 1.0) but the Lead or Tungsten/Tin slug portion was replaced with a Bismuth/Tin alloy slug.  When this ammunition was fired at elevated temperatures the Bismuth/Tin alloy (a eutectic or low melting point alloy) became mushy and the bullets did not all stabilize properly and did not fly right, thus died the M855A1 Version 2.0 attempt to make a green bullet.  Actually this effort was also not all that well researched either because no one seem to have remembered that Bismuth/Tin alloy(s) are eutectic low melting point alloys, which almost all engineers know or should know well.

Now to the current M855A1 (Version 3.0), an entirely new design with an exposed steel penetrator seen in the picture as a Brown colored part of the projectile point, behind that steel penetrator, within the guilding metal bullet jacket is a single copper alloy slug.  So the Version 3.0 M855A1 projectile does not in fact use the failed Tungsten/Tin alloy slug or any related materials at all.

All of that said however this whole Army green ammunition project has been extremely expensive and ill conceived to date and in retrospect.  It is very questionable as to whether or not the latest Version 3.0 is indeed any better or even equal on soft (tissue) targets, i.e., enemy troops than the old M855 projectile that it is supposed to replace.  It is however much better at defeating hard intermediate barriers, such as 3/8" mild steel, concrete blocks, auto windshields, truck doors, etc., but that is in an open environment like Iraq and Afghanastan.....if we ever have to fight in Central or South America the designed in tendancy of of this projectile type to break up easily, on tree limbs or heavy vines (and various other intermediate barriers such as Chinese Level III body armor) used as cover and conciealment in jungle and tropical forests will severely limit it's effectiveness, especially for our special forces troops who may have to fight there.  But that's for some future war(s) and other people to think about.......enough money has already been spent (wasted?) on three failures in a little over a decade....  Yes, I know this sounds harsh perhaps but those are the facts as I see them having spent more than 45 years in the field.

 No need to appologize Hugh. I admit my knowledge of this is limited, and it sounds like you have direct intel on the development of these alternative ammunition lines. Since we seek to know the truth here at FP, your input is welcome, even if it is corrective. Feel free to add your wisdom at any point in the future on subjects such as this of which you have knowledge.