See post #13 for the answer. I've done a little reloading since 1974, and have about 45 die sets in the "tool boxes" . I've reloaded calibers from 380 ACP to 45-70, including one wildcat, the 30 Herrett. I loaded enough ammo to shoot out the rifling on a TC barrel, 1500 S&W rifle, and a custom stainless steel barrel on 25- o6. So this is the tale of interest. I was asked to reload 270 Winchester brass into new ammo for sale at the Outdoor Range. I cherry picked the "best brass" out of 2 five gallon buckets of range brass and got 300+ pieces. I was looking for 'normal' primers, 270 Win head stamp, no signs of difficult extraction, only factory once fired brass without sizing die marks. I checked the decapping stem on my 270 Win sizer die: diameter = 0.275", checked the Speer bullets: diameter = 0.277". Now the fun begins. About 50% of the brass will not pass a new 270 bullet through the case mouth, but a .257 bullet drops through with clearance. There are NO scratches on the case neck or shoulder. The neck ID measures between 0.263" and 0.268". The max case length for 270 Win case is 2.540" . Sized cases measure 2.530" to 2.543" . There is a wildcat cartridge called a 6.5 - '06 shooting a 0.264" bullet, but case length is 2.494" (same as 30-06). How can once fired, factory ammo have "fired necks" that are 0.010" to 0.015" smaller than loaded ammo? This is a simple question about a physical dimension on a fired brass case. No need for a statistical study on accuracy of my Mitutoyo dial caliper or 1" micrometer. Bullet OD was measured correctly and case mouth ID was consistent either at or near 0.265" or 0.279" . EDIT: For you Legal Hairballs, the range has the correct FFL and I am a range employee. Now get over it. Why are the brass case mouths smaller?