On the 6th of December of 2017, I had the opportunity to visit Glock in Smyrna, GA and go through the factory. I learned many interesting facts that relate to these questions.
Another interesting note, Glock manufactures in-house every single component of the pistol down to springs and pins. All tooling, molds, fixtures, gauging, etc is manufactured in-house in Austria. This allows Glock a unique opportunity most US manufacturers do not exercise. Most US gun manufacturers manufacture certain components in-house but subcontract out others. They may also send parts outside to get heat treated, finish or any other coatings. Whereas, Glock has 100% control.
As far as process in manufacturing in the US, it is absolutely identical. All CNC machines come from Austria and have been programmed by the same people who do it in Austria. In fact, the electrical current in the US facility is European instead of American. Even the concrete floors in the US facility are identical to the Austrian plant. The US hammer forge barrel machines also come from Austria. The mold machines manufacture both frames as well as the polymer Glock gun cases the pistols are received in. Those cases would be too expensive and bulky to ship from Austria. To assure ability to produce without interruption, Glock USA keeps one year worth of production materials (steel, polymer manufacturing materials and so on) on hand.
The guns production capacity of US made guns peak last year was 10,000 per day (3 shifts running 7 days a week). Average production is about 25,000 guns per month. That is just US production numbers. The Austrian made guns come disassembled and are assembled and test fired in the US facility. Glock USA has about 25% of the production capability as the Austrian plant. The American facility employs over 400 people. As of December of 2017, The American Glock plant is running at 65% capacity with their most popular model being the Glock 19.
In Austria, Glock has two different facilities, one deals with metal components and the other deals with the polymer components. All research and development are conducted in Austria. There is no model shop in the USA facility. All Glock models can be manufactured in the USA facility. But 100% of the G42 (380 Auto) pistols are made in the US due to ATF import regulations. The 380 Auto caliber Glock pistols do not meet the importation points to be imported into the US.
The test firing procedures at Glock USA is quite interesting. Each pistol is tested with 2 proof cartridges and 5 standard cartridges. The pistols are inspected before and again after test firing. The fixture is fully automated. The pistol with the loaded magazine and slide open are dropped into a fixture. The fixture is closed, securing the firearm. The tester pulls the slide to the rear to chamber a round. Now a bullet proof clear door closes protecting the tester. The tester pushes a button and the pistol shoots all ammo to lock back. Every pistol does this process. Additionally torture testing can be done this way as well. The pistols are tested for accuracy and sight alignment during this process. The range used is 25 meters. The testing facility is top of the line with constant air circulation and filtration system.
Glock USA is housed in several buildings on Highlands Parkway in Smyrna, Georgia. The headquarters at 6000 Highlands Parkway is the original facility that was bought by Mr. Glock in the early 80's. Originally, it was set up to assemble and test fire pistols and to distribute. In fact the operation was quite small at that time and he leased parts of the building out to other companies. As production grew, and when the tenants contracts were up, Glock would expand until the building was full. Today the original building is mostly administrative. The manufacturing facility is right behind the original building. Down the road you have Glock Professional which is the training facility. Here there is a state of the art range and classroom for armorer and operator classes. Down the road from that you have a facility that deals with web store and media including a large photo studio and broadcasting room. There is also a building that houses Glock Medical, which manufactures products for the medical industry.
Identification of Austrian or American made pistols is quite easy. As previously stated the only components manufactured in the US are the frame, barrel and slide. The rest of the components come from Austria.
Hopefully this will shed some light on the Austria vs. US guns. There is not one better than the other. They are made from the same machines and with the same materials, and strict standards that Glock has set forth in both facilities with 100% quality control.