I just built an AR 9 upper with a wilson arms barrel.This is the best 9mm upper I have ever built, it feeds and chambers every weird boolit I cast from 90gr. to 155gr. This is new to me because I have a rash of 9mm barrels with shortttt throats. The funny thing is the barrel with the longest throat seems to be the most accurate. It is also the most expensive 9mm carbine barrel I have ever bought, guess I got what I payed for.