Excessive exposure to lead in indoor and outdoor firing ranges poses a health hazard to shooters, instructors, and personnel who work in or near the ranges. The sources of this lead exposure at the firing point include lead styphnate primers, all-lead bullets, and jacketed bullets with an exposed-lead bullet base. This latter group includes all conventional full metal jacket bullets and some jacketed hollowpoint bullets. Released in mid-1994, the patented Winchester Super Unleaded primer also includes a milder, nitrocellulose-based secondary explosive, a common sensitizer, and the proven igniter pyrotechnic combination, boron, and potassium nitrate. Independent velocity and pressure tests conducted by the Navy's Crane NSWC confirm the Winchester lead-free ammo exactly duplicates the ballistics of the Winchester lead styphnate primed ammo. The muzzle velocities, chamber pressures, slide impulse, and bullet trajectory are the same. Winchester developed a solution to the exposed-lead base of the conventional full metal jacket bullet. They added the "gas check," which is a brass cup that is usually wrapped around the bullet base on all-lead, magnum-velocity bullets; this reduces both gas blow-by and barrel leading.