What does length have to do with velocity?
Short neck, short case, long bullet pushes into the case reducing the space for powder. So smaller powder selection that will hit max pressure without serious powder compression. Same problem the 180gr Partition has.
You've measured 3000fps on a chrony using a TTSX with sane loads? What's the specifics, wouldn't of thought it would break 2900. Makes it interesting since most loads for even shorter 130gr lead bullets top out just over 3000fps in the books.
