Premature ignition of ammunition from heat in the chamber, known as cook-off, was a major problem with early prototypes of the G11 where synthetically bound nitrocellulose, formed into blocks, was used. Normally, when a cartridge is fed into a chamber, its case insulates the propellant from igniting until its impact-sensitive primer is struck by a firing pin or striker. The case aids in insulating the propellant from the heat of the chamber and it takes time for the temperature to rise sufficiently, inside a chambered round, to ignite the propellant. In addition, in a traditional rifle, extracting a hot case removes heat from the system. As a result of doing away with traditional cases, the G11 became a safety hazard and had to be withdrawn from the 1979 NATO trials. The high rate of fire and lack of cartridge cases made cooking off a significant problem since the heat buildup in the G11 chamber was immense, due to the chamber having no provision for cooling, as with a reciprocating bolt system which allows hot air to leave the chamber when the bolt is retracted and the chamber is exposed to air. The vertically swiveling chamber furthermore made gas sealing at each end at such high pressures impractical, as opposed to a cross-sectional round-inside-round bolt-to-chamber fit with appropriate gas sealing.