Very BIG shell casing

My fired just recieved for Christmas a very large shell case. The headstamp is as follows US anchor lot 763 6 IN 47 CAL MK 4 NS 8 1944 JRP and on the primer is 7m 394 HLT 143 MK 13-1 H 44. any and all information would be appreciated. Thanks Vic

Used in 6"/47 MK 16 guns found on many WW II Light Cruisers. A cartridge case found in many big-ordnance collections. Projectiles too.