The Roco Panzer III is one of my favorite vehicles. It is reasonably detailed and accurate, it's been around over 50 years and given good service due in part to it's durability. Still, it always bothered me there was no bow machine gun.
So fix it! I visited my local craft store and checked out the bead section. I got some tiny little bitty glass beads. Sort of flat, but with rounded edges and a hole in the middle, because it's a bead. They come in a pack of a zillion of them for almost nothing.
Next you need a little tiny wire, smaller in diameter than a paper clip wire. K&S sells all kinds of wire and they sell them in craft stores and hobby shops, particularly train stores. But any very small diameter wire will do. Cut off a piece of wire the length of an MG34 machine gun barrel. Very small, about 3 or 4 millimeters. Pro tip, when cutting the wire, put the short end into a bit of modelling clay. Then cut it. That way the small bit of wire is less likely to fly across the room and disappear into the carpet. Wear eye protection and don't use your good sprue cutters for cutting wire. Use wire cutters, don't ask me how I know this.
Dig out your pin vise and using a tiny drill bit the size of your wire to create a hole in the front of your Panzer III hull. That's where your machine gun will go.
Put the tiniest drip of regular model glue in the hole and an equally small drop of CA glue on the back side of the glass bead. Insert the wire into the hole in the bead, then put the bead over the hole in the front hull of the Panzer III. Jiggle the wire around until it enters the hole in the plastic Panzer III hull. All done.
The model glue will hold the wire in place in the hull. The CA glue will hold the wire in the bead and hold the bead onto the front of the tank hull. I usually cut the wire a little bit long as any excess length can be pushed into the hull or cut off after the whole thing has dried.
One pack of those beads is enough for a Panzer Division of Panzer III. This upgrade is quick and easy and in-expensive.
Mike Bunkermeister Creek