2 percent?
doesn't sound like they are exactly "in common use", meaning that a ban on them would be consistent with the second as per the heller decision.
is there any reason why a civilian needs military style firepower?
ummm, there are more than 5 million of them, of JUST AR-15, that doesn't include all the other style of AR rifle. Combined in total you would be talking in numbers of 10-15 million.
Highest numbers of rifles sold by model
Marlin model 60 ........11 Million
Winchester Model 1894 ...........7.5 Million
Ruger 10/22 ...........6 Million
According to this, the AR-15 would be the 3rd or 4th most popular Rifle OF ALL TIME!!
In common use?
One of the common mistakes in statistical analysis is using inappropriate methods, such as dividing the 6 million of one type of rifle into the total existing number of guns , as if there were only 2 types of guns, the AR-15 rifle and everything else.
There are rifles, pistols, revolvers, muzzle loaders, shotguns
Of these types of firearms there are variants of each. like in rifles, there are semi auto, single shot, and bolt action.
You didn't even take the first necessary step in trying to make an accurate measurement.