[jrhead75]

The crown and BNP is the Birmingham Nitro Proof mark, commercial proofing required by law in the UK...applied post-service.

As for the sling...the ends get passed through the swivels, bottom to top, so that the flat side of the rivets on the ends (if there is a flat side) is toward the wood, and the hooks are facing out.

As seen in this picture (although the butt end loop should only be a hand span wide in order to be correct).

 

[jrhead75]

Perhaps other forum members with service in the British Army could shed some light.

That's where I'd originally heard that, although I have seen pictures of the sling as you describe (the cover of the LES, for example). I'll certainly concede to those that have actually carried the things.