The powerful recoil and heavy weight of the 7.62mm NATO cartridge used in Portuguese rifle-caliber arms such as the m/961 limited the amount of ammunition that could be carried as well as accuracy in automatic fire, generally precluding the use of the latter except in emergencies. Instead, most infantryman used their rifles to fire individual shots. While the heavy m/961 and its relatively lengthy barrel were well-suited to patrol operations in open savannah, it tended to put Portuguese infantry at a disadvantage when clearing the low-ceilinged interiors of native buildings or huts, or when moving through thick bush, where ambush by a concealed insurgent with an automatic weapon was always a possibility. In these situations the submachine gun, hand grenade or rifle-launched grenade often became a more useful weapon than the rifle. Spanish rifle grenades were sourced from Instalaza, but in due course, the Dilagrama m/65 was more commonly used, using a derivative of the M26 grenade made under licence by INDEP, the M312.