The Drifter Crossbow is the Military Spec upgrade to the standard crossbow. It is still silent, and it fires every bolt type: standard, Residue, Incendiary, Poison and Explosive. It is the best special weapon for stealth.
Standard bolts give silent kills on guards and sniper nests. Incendiary bolts let you burn Infestation nests without walking in. Residue bolts start fights between Freakers or humans while you watch.
It does the same silent job in a better condition and handles every bolt type. Once you have it, there is no reason to carry the old crossbow.
Get a kill with each bolt type for Variety is the Spice of Life. Thorn In Your Side lets you recover some bolts, which saves parts.