Originally Posted by Vrodryda
Can anybody give my some advice?
Try cleaning and re-lubing the bolt, and/or replacing the back breech o-ring and lubing that up as well.
Keep in mind I'm new here, so my advice probably isn't worth much, but when my G4 stopped firing halfway through my first day out with it, I did a good amount of troubleshooting and this is what fixed it. Also make sure you use one of the lubricants recommended here. My marker didn't like my field's hater sauce for some reason, but works perfectly with lurker lube.