Hello ezman!! REALLY NICE Rig, except for the broken holster strap. Serial Number 44d for a 42 byf was completed about February 1942. Proper magazines for this pistol will be "fxo" type, either aluminum or black plastic bottoms, without any markings on the bottom. I wish it were mine!!
Whoops, I forgot!! All letter series of Military Mauser Lugers had 10,000 pistols. Startind at 1d and finishing at 9999d, in your case.