New builds, 7.62x39mmUSA kinda like a 300/221XL

[MartytW]

bunch of smarty pants J/K

But seriously, all my drawings show .253
Cartridges of the World, 8th Edn
Designing and Forming Custom Cartridges - Ken Howell (the Blue Book)
Handloaders Manual of Cartridge Conversions (the Green Book)
Norma Reloading Manual
Just to name a few

Reason I asked originally was because I wanted to know if moving the shoulder down the case required a change in case mouth wall thickness. Now I am totally confused ...