Five South Dakota lawmakers have introduced legislation that would require any adult 21 or older to purchase a firearm "sufficient to provide for their ordinary self-defense."

The bill, which would take effect Jan. 1, 2012, would give people six months to acquire a firearm after turning 21.

The provision does not apply to people who are barred from owning a firearm.

Nor does the measure specify what type of firearm. Instead, residents would pick one "suitable to their temperament, physical capacity, and preference."

The measure is known as an act "to provide for an individual mandate to adult citizens to provide for the self defense of themselves and others."

Rep. Hal Wick, R-Sioux Falls, is sponsoring the bill and knows it will be killed. But he said he is introducing it to prove a point that the federal health care reform mandate passed last year is unconstitutional.

"Do I or the other co-sponsors believe that the State of South Dakota can require citizens to buy firearms? Of course not. But at the same time, we do not believe the federal government can order every citizen to buy health insurance," he said.

Megan Luther contributed to this story.