i love your assault rifle a suggestion for getting the clip to stay in i would use some rubber slip resistors you know the things you find on the bottom of a laptop to keep it from slipping off the table that might help but it think the main reason as to why the clip comes out so easy is so that you have room for the bondo and other things that you might put on it to make it stronger but all in all i am impressed with your build i have been doing this for 3+ years so i have a lot of experience behind me so if you have any questions on anything at all or need help with something i would be more than happy to supply any answer or advice you may need 
happy building bro and good luck
happy building bro and good luck