Remove the trigger group. Check the carrier latch engagement tab for damage. Ensure it's engaging it's slot enough for the end to be flush with the opening. Move it by hand back and forth and feel the spring pressure; it should be fairly stiff. If weak, you may have a damaged/collapsed spring.
Last, there's a small, black finger-like tab that sticks out horizontally towards the muzzle end, alongside the carrier latch. It's a shell guide. Ensure that did not become a bit bent and might be interfering with the forward movement of the latch when it's engaging it's slot.. The latch should move close to it, but definitely not touching it..
The fact that it works when you work the action manually tells me that there's something interfering with full movement of the carrier latch when the speed of firing is involved..
If nothing else (and you're completely confused
) take that other trigger group out and place it directly alongside yours and note any potential differences between the two in the latch and/or tab area..
Let us know what you find..
