How many pounds of pressure does it take to fire a 5.56 mm round?

Answer 1

If you are referring to how many pounds is the trigger pull weight for a rifle that fires the 5.56 NATO round, that will depend on the rifle. Some may have a "benchrest" target trigger pull of 2.5 lbs, which is too light to safely use for most NON benchrest shooting. Others may have a 6 lb pull. There is no one standard.

If you mean how much force on the primer to fire a cartridge- only enough to dimple the outer cover of the primer, and pinch the priming compound against the anvil. A few pounds, concentrated on a very small spot.