TM GLOCK 18c issue
 

My g18c seems to loose fps and doesn't blowback after shots. I took a look at the bbu and everything is secure and in good condition, no cracks or any physical damage visual.
Although, the gun will shoot if my mag is shifted to the rear of the gun as there is about 1/8 inch of play in the mag well.

Any ideas what is wrong?

There was a tread about a similar issue made not a day ago.

http://www.airsoftcanada.com/showthread.php?t=144939

E luder kindly wrote a pretty good potential solution to your problem.

Cheers

Another cause might be that the plastic magazine catch has worn down and no longer holds the magazine against the bbu tightly, or in line with the firing pin. The solution is simple: replace your magazine catch with the steel upgrade one (forget the make, think it's guarder). One of my teammates had this problem and replacing the catch did it