I recently got a Classic Army M15a4 and since its a Seal Version i decided that i wanted to build a carbine length upper receiver to fit. When i test fit an M4 receiver i noticed that the front receiver pin hole didnt line up and it was extremely loose. When i bought the receiver i was told it was a Socom Gear DDM4 upper receiver. Then when i try my DBoys M4 RAS2 upper it fits fine with minimal wobble. Can anyone fill me in? And i know about the "old type" and "new type" difference but thats not the issue here.