“in a DU tank shell,
or any other such projectile,
does the DU material come in contact
with the rifle barrel?”
No, these are “discarding sabot” rounds. The DU penetrator, basically a dart, is surrounded by a lightweight, two piece jacket, the “sabot” (Fr. “shoe”).
The sabot flies off as the projectile leaves the muzzle, leaving the heavy penetrator to fly downrange. This is used because a full-caliber DU projectile would either be much too heavy for effective velocity (or even firing safety), or much too short for usable aerodynamic and ballistic properties.
This was invented during WW2, not for protection from toxicity, but to allow the use of dense, sub-caliber armor-piercing projectiles (orignally tungsten) in high and medium velocity tank and anti-tank guns.
Discarding sabot rounds are available for certain small arms, the idea is to use a lightweight bullet with a large caliber charge for higher velocity.
oK, what is the ‘dust’ hazard?
cleaning up a tank battle?
cleaning up something shot up by an A-10?
other?