Another Friday tank, did you and DAP order yours at the same time from the same people?
The screws are M3s. I told you HL wanted you to get the full realistic effect of tank ownership. How many Tiger's do you think the crews picked up at the factory and went right into combat with them? Only the first few, their tanks were lost! Panther's were the same way.
One of my PZIIIs had spare wheels jammed inside the board when I opened it up for the first time.
The BBs are gravity fed, sometimes you can shoot and another round won't load right away if the magazine is fairly empty and you're bouncing it around the yard. Might as well take the airsoft unit apart now, check for "flash" where the ammo loads and secure the rubber bushing inside the breach with a dab of CA.