Sure have! Built one for my son and grandson three years ago for Christmas. 100% Rock River Arms in a 16" A4 and put an EOTech on it. It is a tac driver! I built it for them since they live in the city and have a couple of indoor gun ranges and they can not handle high power rifle rounds. Works great for them since they can shoot even in the winter in Indiana when the weather is bad. Let me tell you the little rifle shoots fantastic. Of Course the ranges they shoot on are 25-50 yard ranges but it will stack them even with cheap 9mm ammo. I had some fiocchi ammo which I will never buy again!
I think they load them with powder and coal dust!
Dirtiest 9mm ammunition I have ever seen! And God I bought a case of it!