Trigger-happy Australian soldiers have been warned not to shoot so much, except in an absolute emergency.

If they just blaze away and exceed recommended rates of fire for automatic weapons, they could face serious injury or even death, authorities have said.

A defence spokesman said there had been a number of such incidents in the past three years, most on live-fire ranges in Australia.

The key risk appears to be what has been termed "cooking off", where a buildup of heat leads to ammunition firing inadvertently.

"If the weapon is not allowed to cool down, it will overheat," the spokesman said. "This heat may cause spontaneous combustion of the propellant in the cartridge, irrespective of whether the cartridge is correctly chambered or about to be chambered in the weapon."

The spokesman said the ensuing explosion could damage the weapon, making it inoperable until repaired.

The issue was raised in the latest edition of the Army newspaper, which said there had been a significant increase in incidents where personnel had exceeded recommended fire rates.

That applies particularly to the F-88 Austeyr rifle and F-89 Minimi light machine gun, both widely used by Australian troops in Afghanistan.

Defence small arms policy and safety staff officer Major Paul Hopkins said Army defence policy was that fully automatic fire was only effective at short ranges and then only in bursts of two or three rounds.

Longer bursts were almost impossible to fire accurately and generally wasted ammunition.

Major Hopkins said the defence weapons pamphlet specified a maximum rate of fire of 90 rounds a minute for two minutes.

"Some ADF personnel have misinterpreted this and assumed that it's permissible to fire six 30-round magazines on fully automatic as quickly as possible," he said.

That's now been revised to specify a sustained rate of fire of 30 rounds per minute in two or three-round bursts.

"This rate of fire is not to be exceeded except in an operational emergency."