KWA M11A1 Not Blowing Back
 

I have a M11A1 that is about 2 years old, but hasnt been used in over a year because it doesnt blow back. I thought it was a problem with the magazine, because it had a little crack in it, but I just got a new one, and the mag isnt the problem. It shoots, but does not blow back in semi or full auto. I have kept it lubed and maintained, any suggestions?