About 5 years ago I built a 9 MM carbine and just got in a 7.5" complete upper for a 9 MM. Put it together and I had and extra charging handle the I tried to use and it would not fit into the upper. Does the 9 MM use a different size charging handle? I had 2 other of the same charging handles that I used in a 223 and 300 BO piston without a problem.