THE GMG42 DRUM MAG IS A METALLIC MADE MAGAZINE and HAS A CAPACITY OF 1700 BB'S.
THE DRUM MAY INCLUDE A PRESSURE SWITCH SO YOU CAN EASILY LOAD BB'S WITH ONE BUTTON.
THE BATTERY that goes in is a 7.4V.
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.