Their website says drop box megazine, though the bottom plate is not the rigby type.

I have just received my custom built gma actioned 416 rigby. It only allows 3 rounds in the megazine. One can load the 4th round into the magazine but the bolt does not slide over it even whilst depressing the round. I See the actions by golmatic prectl, john rigby and MAUSER'S new M98 have a deeper bottom plate unlike the gma actions, yet Gma in their website call the action as having a drop down megazine. I really would want a 4 rou nd megazine, is there any way to fix this. I hope daune weibe can clarify , since he does use Gma actions.

I have a 416 Rigby built by Duane on a GMA action...it holds 4 down.

Thanx, did talk to daune and he said you have to make the megazine trapezoid to allow 4 down.