Can anyone ID this part from a 20mm or 30mm canon?

This came with a load of high ground wreck parts recently. The previous owner can’t remember what it came from but I know he did visit some jet sites, including a Javelin. It’s made of high quality thick steel and looks the right shape to conform to a 20mm or 30mm round. I’m wondering if it came off either a cannon, feed mechanism or a magazine. Of course I could be completely wrong and it might have had a totally different function – this is just a hunch…

Does anyone recognise it?