In the Cobra, the weapon is supplied with a magazine of 700 linked rounds, with a total capacity including feeder system of 750 rounds. It has a cyclic rate of fire of 650 rounds per minute. Standard practice is to fire the cannon in 30 to 50-round bursts.
The M197 remains in use in the latest AH-1W Cobra and AH-1Z Viper gunships. Although the weapon's rotary drive is theoretically quite reliable, its ammunition feed has been anything but: Marine pilots initially reported an alarmingly high jam rate (sometimes greater than 30%). The USMC and the manufacturer are aware of the problem and in 2011 a link less feed system developed by Meggit Defense Systems was incorporated into the AH-1W and the Zulu's. The system is capable of holding 650 +/-3 rounds in the storage unit with approximately 40 rounds in the feed chute.
The M197 is also mounted as a chin turret in Italy's Agusta A129 Mangusta CBT helicopter, with a capacity of 500 rounds.
Nose fuzed round, no tracer. Effective radius to produce casualties to exposed personnel 2 meters, fragmentation hazard out to 20 meters. Penetration 12.5 mm RHA at 0 degree obliquity at 100m range 
Similar to M56 series of HEI rounds, but with a tracer element.
Multi-purpose fuzeless round, HE charge is initiated by the incendiary charge on the nose on impact. Self-destruct due to tracer burn-through. Penetration 12.5 mm RHA at 0 degree impact at 518 m range, or 6.3 mm at 60 degrees and 940 m.