So what parts on a full BCA upper are the biggest kink in reliability? Everything? BCG? Hand guard? If you had one and wanted to make it reliable to your standards would that be possible?

“When Tyranny becomes Law, Rebellion becomes Duty”

Colossians 3:17 (New King James Version)
"And whatever you do in word or deed, do all in the name of the Lord Jesus, giving thanks to God the Father through Him."