polish ammo box?

[michal19]

hello i have in my hands IMO strange ammo box.it looks like a fusion of german mg34/42 and mg13 boxes.the only marking on it is the letter ''m''.on photos are visible the remains of grenn paint,the user of Polish militaria forum told me that this box can be polish issue,what do you think?
best regards

[lebus12]

One friend tell me it's WWI, for the ammunition links, before the 08/15 dum.