For those curious about the differences between M14 and Beretta BM 59 Magazines.

The M14 magazine “rocks” into place. That is, you insert it by pushing it top front edge in the front of the well first (and briskly), then “rocking” the rear of the magazine up until it catches the latch.

The BM 59 magazine goes in straight up and straight down, kinda like an AR-15, despite latching at its rear.