The G&G PRK9 40-round magazine is a mid-capacity airsoft magazine made of high-strength polymer with dummy bullets inside. It is designed specifically for compatibility with the G&G PRK9 series of AEG (electric airsoft gun) rifles. 
 
Key Specifications
According to various retailers and the manufacturer's information, the key specifications are:
Capacity: 40 rounds (mid-capacity/low-capacity, depending on the retailer's classification).
Material: High-strength polymer construction.
Compatibility: Exclusively designed for the G&G PRK9 AEG airsoft gun series.
Features: Often features smoked, semi-transparent plastic with dummy bullet shells inside for enhanced realism.
Weight: Approximately 103g.