This is the 5 round factory rotary magazine in .308 for the Steyr Model L, also fits the Steyr SSG.
The magazine has a hunting scene on the base vs the SSG logo on the SSG model, otherwise the same.
The rotary magazine design is flush fit to the stock and is made of a tough polymer with a clear viewing plate at the rear.
Please note version is the 'squeeze to release' magazine type, early versions of the Model L with magazine releases on the trigger guard use a different magazine.