It was a local modification that had no official sanction in the EMER's but was accepted by all, You might not even notice it as the cursor slide was skimmed and the backsight axis pin part of the leaf was slightly cleared to allow the bolt head to pass. Seen plenty and done them too....
It was a bit like finding a leather sling on your No4T. That's how it was issued but when the snipers got them, they put the long Bren slings on
And does anyone have a rifle with a modified sight. Yep, I do. And a webbing Bren sling too........... Yep, me again