Some estimates indicate that there are in the neighborhood of 3.7 million AR type rifles in the US or about 1% of all guns in the US. I wonder if that qualifies for common use.
I think those estimates are off a bit.
Regardless with there being only 110,000,000 rifles and the huge number of types 3% would make a huge percentage. Probably the most popular single type. Like a Ford F series truck.