ProWin is known for creating high quality airsoft products. From magazines to internal parts. Their recent release of their 41rds magazine for 5.1 and 4.3 is a great addition to their lineup. The outer shell of the magazine is made out of CNC Aluminum for the utmost amount of durability. The overall weight is much more lighter than the standard 5.1 Magazine. The extended magazine is designed to be used in IPSC Shooting where speed, accuracy, and duration is important.