If the neck of the cartridge is straight, how can the bullet seat anyway but straight? Ohhhh, I'm pretty sure I'll regret asking that question..
No sir, its a legit question and deserves an answer.
Regardless of the neck of the brass, if the seating die isn't lined up perfectly the bullet can be set cock-eyed. Hard to tell but if you spend the loaded round under a dial indicator you can see it.
I have a report somewhere about Lake City having accuracy problems with there 5.56 ammo, causing it to fail the Army's standard.
The army uses a Mann Accuracy device to test their ammo. They issue these devices to ammo suppliers. When LC failed the standards they blamed the Mann Device. The Army tested the device and determined it was accurate.
The Army made up some special hand loads and tried them in several Mann's and they, including Lake City's, pretty much shot the same groups.
Further investigation found that the machines seating the bullets were worn and out of alignment causing the bullet to go in cock-eyed, again this couldn't be detected by the human eye, but spinning under a dial indicator does show the alignment. It doesn't take much. If the bullet starts down the barrel while wobbling, its not going to be accurate.
As a side note, the CMP sells these Mann Devices. I got one in 5.56 and I could see a big difference in loading my ammo when I ran them through the Mann.