FAS 604 puzzler

[mrgeoff]

Think it’s to do with the long rod, with spring on, that attaches rearward under the grip.

Try adjusting the nut which secures this rod.

[Wilyoldtrout]

Thanks Geoff, the long rod seems to be the key to the problem. I've tried it at the full extent of its adjustment both ways (and even completely removed). No joy. Like I say, it's a puzzler.