Which, I assume, is exactly how the Sarco actions are made.
My brother's Chinese girlfriend is in the business of connecting western buyers/companies with Chinese manufacturing.
Everything is scrutinized at every step of production on through packaging and shipping the finished product. If it doesn't meet the buyer's requirements, she finds someone else that will make it.
Just because Sarco or whoever commissioned the production of these actions is willing to accept them as produced is no indication of the ability of the manufacturer to make them better. They are made to a price.
To insist that China doesn't have the capability, skill and materials to produce actions on par with Prechtl, Mayfair, GMA or anybody else is naiive. All of the materials and equipment are available on the open market and a rifle action is a very simple item to produce compared to scientific and tech market demands.
Tell me if those action makers have a shop like this. Doubt it.
http://www.china-machining.com/equipment.htm