Bartlein CFW goes shorter than 20”, I have 6.5 and 7mm barrels at 19” for a 18” finish length, but they go down to 17” for 16” finish length:
https://shop.otmtactical.com/bartlein-65-carbon-fiber-blanks-remington-varmint.html
I went 67.0-68.0-69.0 N565 with virgin ADG brass and the 175 elite hunter and a 215M primer. Took the brass out of the box, primed, powder, seat bullet, send. No issues whatsoever. 69.0 got 2,990 on a 24” Bartlein.