Also this is a blast from the past, but Liberty Ammunition did develop a tungsten 110gr (!) 5.56 load around 2012.
>https://web.archive.org/web/20120605090500/http://www.libertyammunition.com/products/liberty-ammunition-5-56x-45mm/
Also a tungsten 360gr .338 Lapua "T3" - that must have been something.