The engineering of the automatic action requires a gas port. The gas port bleeds back some of the hot gases (pressures) produced by the burning powder. These gases help operate the bolt action in the receiver – to eject and reload the next shell. The diameter (size of the opening in the gas port) is determined at the factory. The gas port diameter is set I size for a particular type of shotshell.

Years ago, narrow ports were set for lead loads. Today the gas port is set for steel loads. The gas port is larger to allow greater flow.

Recoil (setback) is also a function of shotgun automatic actions. Setback assists the ejection of the fired shell in coordination with the gas port moving a piston or twisting a cam to unlock the bolt and ejecting the fired shell.

When an automatic shotgun (which is manufactured for steel loads) is used for lead loads, HeviShot™ loads or any other shot heavier than steel pellets… the combination of increased recoil (setback) from the heavier load and the rush of pressure down the gas port – overwhelms the automatic action. The hull may become damaged owning to the premature opening of the action. (Lingering internal barrel pressures or because of the aggressive thumping of the action.) Damage to the action is a possibility.

Your Solution:
Carefully read the handbook provided by the shotgun’s manufacturer. They often warn the owner to only use steel loads in automatic shotguns. (Because the shotgun was designed for steel loads.) Problems increase when the shotgun has 10-gauge or 12-gauge 3-1/2" chamber.

If the shooter wishes to fire differing shot types - anything heavier than steel shot – the solution is to purchase a pump action. With the exception of steel shot being used, any heavy field automatic-action shotgun may fail to operate "normally." A pump action is a better choice for shotshell change-ups. Pumps operate with any type of shot or weight of load.

The Reloading Curmudgeon