Any Idea What This Is?

[DannyZall]

Basically I want to know what this is and how to replace it (if possible) as when I pull back the charging handle to adjust the hop it should lock the cover back, but it just sends it forward without my help I'm quite lost on what I should do here any help/advice would be well-received, thanks. 

Forgive me for one of the photos being upside down 

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[BigStew]

can't help but you might have more luck saying what manufacturer and what model the gun is.  

 

[DannyZall]

can't help but you might have more luck saying what manufacturer and what model the gun is.  

Click to shrink...

Its a nuprol delta sopmod

 

[Lozart]

It's a bolt hold open catch. I need one for a build I was doing (based on an E&C gearbox and receiver) and the only place I could find one in stock was New Zealand.

This is the part https://www.evike.com/products/45687/ but it might be worth checking with @ak2m4 to see if he has any kicking about.