I spent a weekend earlier this month building a pair of .30 Cal BMGs from parts kits.
It took about 5 hours per gun (three of which were spent finishing the 70% receiver plate). Lots of dremel/grinder work followed by two sore hands from using the hand file.
Just took #2 out for a test drive and it ate 140 rounds of South African .308 without issue.
These are very fun (and HEAVY) firearms!
A couple pics from a proud papa!
Cool, huh!?