Analysis of information sources in references of the Wikipedia article "Shooting brake" in English language version.
If milord had it in mind to do a bit of hunting, he and his guns would then be transported to the shooting site in a "brake" (the English term originally applied to horse-drawn wagons). Being somewhat logical, the British determined that if a brake was used for shooting purposes it might well be named "shooting brake." However, the term fell into common parlance and eventually became a generic label...
shooting-brake.
16. Wagonettes. — This type of body should have longitudinal seats placed vis-a-vis in the main portion of the body and usually with a hind entrance, although some varieties have side doors as well. A shooting brake is a wagonette provided with game and gun racks, and accommodation for ammunition. A luggage brake, or estate wagon, is often a wagonette with the long seats made to fold flat against the side of the body and the hind entrance provided with double doors.