@TomJefferson - Sounds likely to be the case.

@nightops - Yes, it's the attachment itself.

Confirmed from me. Happens in our group every single day, almost every other group of shots there'll be at least one of us that doesn't hear anything even when we're all together and the shots are close.

I just posted this same issue, #0007750, before seeing yours.

This has happened to me on several occasions, most recently a couple of hours ago. I too had piles of 60 .556 rounds inside it. Seems to happen randomly though as I've had boxes full to the brim with 600 rounds in and not had it happened; then other times it just disappears.