Is there a trick to this? Seems pretty straightforward in the M4 videos I've seen, just insert the charging handle, give it a turn and it clicks into place. I'm inserting mine and turning it this way and that way and nothing is clicking or locking in. The handle just pulls right out. I've tried with varying amounts of pressure, wiggled it all over while turning, nothing is working. Do you have to hammer this thing in or something? Brand new gun. Appreciate any help.