I understand the theory but the bolt is not solid in the carrier nor is the carrier solid in the upper. Maybe I've just never seen an upper far enough out of line in the few dozens I've seen.
I do remember back in the day, Paul from Bravo Company told me I should use billet uppers because forged uppers were so crooked... I took it as salesmanship since billet was new and I hadn't seen any crooked receivers yet from him.
Anyway just curious if anyone has proven it made a difference.
