That's what the stake notches in that nut are for
After the nut is torqued to 25-30 ft poundees, you stake the receiver plate into the castle nut.
Then THIS doesn't happen at embarrassing moments.
Complete thread:
- Why You Need To Keep Your M4's Castle Nut Tight - 
Sarge, 
2012-05-01, 23:05 
- That's a mess! - Slow Hand, 2012-05-02, 04:37
 - Have seen this before where it tore the hell out of the - 
Hobie, 
2012-05-02, 06:18
- I thought it rather fortunate... - 
Sarge, 
2012-05-02, 08:06
- Yep.  The one I saw was a pain to get apart as the - 
Hobie, 
2012-05-02, 11:27
- I saw one where the pin ended up inside the buffer tube with - cas, 2012-05-03, 10:00
 
 
 - Yep.  The one I saw was a pain to get apart as the - 
Hobie, 
2012-05-02, 11:27
 
 - I thought it rather fortunate... - 
Sarge, 
2012-05-02, 08:06
 - That's what the stake notches in that nut are for - Miles, 2012-05-02, 19:36