Everybody keeps telling me 9mm (and other autos) headspace on the case mouth. In around 1973 and older marine Master Gunnery Sergeant (in charge of weapons maint. Dept.) told me that the case will not go any more forward than the extractor lets if. He then proceed to display examples of .45 ACP cases from Winchester, Federal and Remington, along with military issue. He pulled the bullets and measured the case length with a micrometer. I was amazed at the variance in length of the cases, even from the same box. I do not remember the exact lengths, but the difference between the shortest and the longest was substantial by cartridge case dimensions. I am not an advocate for or against, but am merely providing information I came across.