hi all. i’ve ran into a big problem. i recently installed the magpul asap by removing the buffer tube and ever since that, the buffer retainer spring and the buffer retainer has been popping out when i stroke the charging handle back. when i charge the handle, the buffer retainer spring and buffer retainer occasionally fall into the lower receiver. i installed everything back correctly. can somebody please tell me what is going wrong or direct me on how to resolve this? thank you for your time.
Maybe the buffer tube needs to be one more turn tighter?
Your RE is not capturing the buffer retainer. This could be because your RE is not forward enough into the receiver OR your RE is moving side to side in the receiver (while shooting) and is releasing the retainer.
So try and give your RE another turn and see if that helps. If you cannot do that without trapping the retainer, then that means that the thread pattern on your RE is not conducive to working with your lower receiver and you might need to replace it.
Post a pic of your retainer in the lower if you can.
C4
As we already know, if the Receiver Extension is not turned in far enough to capture the Buffer Retainer, it will not hold the Retainer within the Lower Receiver.
A couple possibilities:
If turning in the Receiver Extension one rotation causes the Extension to contact the Retainer too much, this excess can be eliminated by filing down of the excessive Extension material. Another option is to take a Rat Tail File, and cut a slot in the Receiver Extension which straddles the Buffer Retainer.
When turning in the Receiver Extension to make sufficient contact with the Buffer Retainer, keep in mind that the Extension might protrude too far at the top of the Lower Receiver to allow the Upper Receiver to close properly.
wow, i can’t believe it… it was my buffer tube. something so simple that i overlooked. thank you gentlemen 
Make sure that you stake the castle nut once you are finished.
So turning the Receiver Extension in one more rotation did the trick? If so, good deal!
Now as IG mentioned above, you should consider staking the Castle Nut.
i did screw the buffer tube one more rotation as advised by the fellow members here. the sad part is when i unscrewed the buffer tube, the buffer retainer and spring shot out and i lost them. i searched about half an hour in the vacinity where i was working on but had negative results… boohoo. its a good thing for replacements parts at really low prices i should be receiving them today and i will be extremely careful and attentive this time. thanks again all!
~~ quib, i’m going to remember staking the Castle Nut, thank bro!