This is an Armor Piercing, Fin-Stabilized, Discarding Sabot, Tracer projectile (APFSDS-T, for short). It is fired from a 120mm smooth bore gun as found on M1 Abrahms tanks. It has no explosive or pyrotechnic components (used to have a tracer, but it's been removed).
Based on what I see on the web, people are asking $80 for unfired projectiles. This one is new, and has the sabot, and part of the cartridge bolted to the bottom.
I figure I'd ask about $50 in trade value. There is no doubt I could get more than that if I put it on some high-profile place like ebay. All I want is to trade for gun stuff.