As production volume increases, it becomes significantly more difficult to maintain a level of quality that you would at lower levels without the right systems in place. Unfortunately, the number of units delivered is often the only number that matters to many manufacturers and they expect a certain number, maybe 10-20% coming back for warranty. Meanwhile the end user has a 10-20% chance of receiving a part that is intentionally wrong. Its intentional because someone deemed it reasonable to allow unsatisfactory product into the market on the hopes you never notice.
In this example, I have gas tubes all from the same place. The three on top came as they should. The two on the bottom have insufficient bends in them. While the exact location fore and aft isn’t extremely important, the amount if offset is. I have found that more often, the bends in nitrided tubes are more likely to be relaxed and not have the required .156″ offset. I don’t know the exact cause of this but I expect it has something to do with heat from the nitriding process.
I believe every tube should be checked for alignment after assembly, and many will need some minor adjustment. However, insufficient offset, especially on shorter tubes like carbine or pistol length in combination with a longer barrel nut can result in binding between the tube and the barrel nut and cause misalignment between the tube and gas key. Misalignment means premature wear at best and a gas key crashing into the tube at worst. It’s your job while fitting and installing parts to look for inconsistencies or systems that don’t operate as they should.
Skilled assembly is ever more important the more we have panic buying or other high volume periods in the gun industry.