http://www.wgcshop.com/pcart/shopper...20for%20Pistol
If you take a look at that picture. The front end of the muzzle. There is a circular entrace and a small rectanguler piece sticking out.
1- That rectangular piece is prone to breaking off. This will cause miss feeds and other irregular bb actions.
2- that circular entrace must remain in its original shape or further failures may occur.