I'd figured that they were even lighter than Bros, so thanks for that heads up.
The Raccoon has left the building.
Even assuming you means 576 g (just over a pound) for a c4#6 and not 5576 g (~eleven pounds), a gipsy is lighter than a #6, not the other way round by the numbers you post but you then say the opposite. your math doesn't add up in any way, shape or form.
also note billcoe took these numbers as straight dope and posted them, errors and all, on a bunch of other places round the internet.