Hello gang. I have been lurking here for at least a year before i signed up mainly because a buddy of mine bought his AR to a shoot 2 winters ago and i fell in love with it. luckily he was a wealth of knowledge and lead me to a few places to find information and products.
i finally decided to take the plunge a few months ago and put one together. its a mega lower with a dd lpk with a bcm lw 16 upper. cant stake the asap for the life of me but ill keep trying.
For staking the ASAP get a spring loaded auto punch, once you get a mark started just keep punching and once you get a decent indentation you can angle the punch toward the castle nut and guide the metal toward it. It will require multiple strikes.
I have no experience with Mega but it looks like a good build. Part of what you are doing is adding to and removing what you feel improves the system for you. I have a carbine like yours that never seems to be done.
It gets really bad when you start buying barrels to swap out.
I would suggest that you save up for a good RDS next.
The all that is left is bullets and practice.