Before the AR-15 became popular, and even predating the M-16 full auto version for military use, the Ruger ranch rifle was chambered for the .223 round they both initially used. It was a good light semi-automatic weapon without a lot of recoil, but its lethality to anything larger than a coyote was questionable. Many states didn't allow it for deer hunting for this reason.

This anemic lethality and the military's adoption of UN standards that made expanding ballistics illegal in warfare created many problems for our soldiers in the VietNam conflict. One of the primary complaints that proved deadly to many of our soldiers was the propensity of the weapon to jam from a combination of too-tight tolerances in the recycling mechanism and the lack of pressure from the round to overcome heat expansion and the grit weapons accumulated in the real world while under sustained firing in battle.

Neither would be problematic in typical home defense or other normal use of civilian weapons. The military solved the issue by switching to the more lethal 5.56 NATO round that developed more velocity and back pressure to cycle the mechanism. The government could make the NATO round illegal on the retail market without disabling the weapons chambered for it, as both will accept the more anemic .223 round.

This could be done along with a limitation to magazine capacity and the existing large capacity magazines made for the 5.56 NATO round would be made unusable as they don't feed the .223 round which is slightly shorter. It has already been proven that Congress has the authority to regulate such criteria and this small effort would go a long way to decreasing the lethality of civilian weapons. It would likely make those weapons unpopular enough to greatly diminish their availability.