Barrett publishes the factory load data on their site. Click the "reloading" tab:
http://barrett.net/ammunition/416barrett 416 BARRETT RELOADING
Brass: Barrett .416 caliber cases
Primer: CCI #35
Powder: Hodgdon US-869
Powder Charge: 190gr
Bullet: 395gr Barrett VLD
Cartridge Overall Length: 4.563 +.005 / -.000
.416 BARRETT CASE DIMENSIONS
Overall Length: 3.273 +.000 / -.015
Trim to Length: 3.263
Headspace: 2.649 +.000 / -.006