This article provides information about different stock replacement options for the GSG-5. You may also want to see more information about the GSG-5.
Many different options
The GSG-5 comes with a variety of aftermarket stock options. The factory stock is modeled after the original MP5 full size stock. I wouldn't consider it high quality, but I do like the length. It is a hollow "light polymer" that is not as durable as the real MP5 stock. I opted for the retractable stock because it would cut down the storage size of the weapon and also looked a little bit cooler. I hated it. It was a little bit flimsy and it cut the overall length by over 2". It dramatically affected the way I operated the weapon and I only used that stock for a short time. My third and final attempt was the UMP-style folding stock. I inquired about this stock as someone was selling it on ebay and he told me it was the same length extended as the "stock" stock. I purchased one and have been more than happy with it. The grip against your shoulder is better and as such my length requirement and storage size requires were also met. I highly recommend this stock. See the images below for a comparison of the stock lengths and what I ended up keeping:
