Hi-Capa 3.8 not chambering

[benchrest]

Hey guys, my sidearm has recently started playing up. Always kept clean etc. However, I load the magazine, pull back the slide, and fire one shot. Sometimes two, and then nothing. But if i pull the slide back again to chamber a round it will. I also noticed the amount of gas its consuming is unreal, i used to get about 15rounds off fully gassed now i get about 5 off!!