The MONTNEEL SYSTEM:
Its pretty nice. Its based on the old Bushmaster system from the 1980s, except the old Bushmasters used a thumbscrew, while the Montneel had a "quick release pin".
The BLAZER uses a system like old Tippmanns. Pretty nice, except I think you need a tool to remove? or is it a thumbscrew?
The Stingray was also pretty nice. Used 2 pins. The only problem was it was TOO EASY to loose those pins!
Nick