I have a BDA.45, bought new in 1980. Mags are "retained" by friction, the mag catch presses on the spine of the mag as you pull it out. And that is the only way to remove the magazine, to pull it out. The gun does not have (and cannot easily be made to have) a drop free magazine.
This is common with a lot of European designed guns. Absolute max speed of a mag change was not the priority of the designers. On the other hand, it is virtually impossible to have your gun put out of action due to the mag catch being bumped and the mag dropping out.
All else being equal (and it almost never is) bigger bullets tend to work better.