THE DRUM MAY INCLUDE A PRESSURE SWITCH SO YOU CAN LOAD BB'S EASILY WITH ONE BUTTON
ALSO, THE DRUM MAY BE SUITABLE FOR MOST M4 REPLICAS.
THE BATTERY that goes in is a 9V block, not included.
Note that with every magazine it can happen that the BB's do not feed properly on a certain brand of replica.
The advice is to try a different brand of magazine, in order to solve the problem.