I recently picked up a few boxes of .223 55gr subsonic FMJ. I am trying to shoot these through a 20" DI AR platform with a Gemtech G5 can. I can not get the rifle to cycle, have to charge every round. I shortened the buffer spring to the length of the buffer tube and installed an empty carbine buffer (took all the weights out) and it still wont cycle. What do I need to do to get it to cycle? Any information is appreciated.