pre-engraved, that is, the rotating bands are cut to engage the rifled bore. If the round was not rotated slightly when loading the M40 it could result in jamming in the breech. Types of ammunition included HEAT, High Explosive Plastic-Tracer (HEP-T), canister, High Explosive Anti Personnel, and the M368 dummy round which could not be fired and was used for crew drill. The original U.S. HEAT round penetrated more than 400 mm of armor. Near the end of the M40's service life, both Austria and Sweden produced HEAT rounds for the weapon capable of penetrating more than 700 mm of armor. Spotting rifle The ammunition for the M8C spotting rifle is not .50 BMG, but a 12.7x77mm (22mm shorter) round than used in .50 caliber machine guns. The spotter round was developed to replicate the trajectory of the 106 mm ammunition, and features a tracer element and a point-detonating incendiary filler to create a puff of white smoke at the impact point. Four of the six 106mm rifles on the M50 Ontos mounted spotter rifles. Spotter rounds has a yellow tip with a red band and practice cartridges had a green tip. Although the spotting rifle could conceivably be used in an antipersonnel role, historic U.S. military doctrine strongly discouraged this use, for a purely tactical reason—to conceal the vulnerable M40 and its crew from the enemy until the main rifle was ready to fire. However, this restriction is believed to be the source of a long-standing misconception that the laws of war restrict the use of .50-caliber projectiles against enemy personnel more generally. Civilian use In the early 1990s, the United States Forest Service (USFS) introduced the M40 for avalanche control as ammunition stocks for its M27 rifles became depleted. The M40 was initially successful due to operational similarities to the familiar M27 and ready availability from the U.S. military; however, in 1995, a USFS gunner was killed by shrapnel after a low-level premature warhead detonation inside an M40 barrel. The accident was attributed to an undiscovered hairline crack in the projectile's base plate. Following this incident, most USFS M40s were quickly replaced with surplus 105 mm howitzers, but a few were kept in service with safety barriers to protect the gunners, who fired the guns remotely. In December 2002, two M40s at Mammoth Mountain were destroyed by catastrophic bore explosions 13 days apart. The gunners were uninjured, having