These BAR cases were originally designed for use with the M1924 Phillips Pack Saddle for the Cavalry.They're different models and equipment for the M1918 BAR,M1917 MG,and pack artillery models.Here's a couple of links with pictures.Bipod equiped models will not fit these cases.
http://mysite.verizon.net/vzeeir49/id19.html
http://www.1919a4.com/forums/showthread.php?p=268376
Like the M1938 M1 Rifle scabbard,equipment originally designed for use by the Cavalry and horses,the usage changed as the modes of transportation changed.