Firstly, ascertain whether it is a REAL DU Projectile…go to a High school or College Physics Lab, and borrow their Geiger Counter…DU still emits Alpha Particles etc. If it is RA (Radioactive), then Place the entire cartridge inside a Lead Tube, with Lead end-caps (you may have to get a Plumber to make it up for you (a very OLD plumber, who has the necessary Lead working skills --Nobody uses Lead in Plumbing these days.).
Label it with a Diamond-shaped Radioactive sticker. Place in a Locked cabinet or safe, away from curious Eyes, and Hands.
DU is what is left in Reactor Rods when they no longer have viable U-238 and U-235 for reaction (Fission) Purposes. The Atoms have broken down into RA Isotopes of Lead and other Metals, which still emit particles for quite a long time…also, the remaining Uranium atoms keep breaking down slowly, though not with the rapidity of a controlled chain reaction as in a Reactor Core. This breakdown will emit Alpha Particles and Gamma rays, the Former of low Penetrance (will fog Photo Film) but the Latter is quite dangerous (will affect your DNA).
Also, check the Local Laws and Federal Law on the detention of RA products…it may be illegal to hold. Your House Insurance may be invalidated, as well.
Better to be safe than sorry…the RA discharge check is to make sure it is not a FAKE.