Remington 870 Express "Blackhawk Tactical" Question

[LocutusOfBorg]

I have removed the two receiver pins from my Remington 870 Express "Tactical" edition, as to install a saddle mount with Picatinny rail affixed.
When I tapped out the two pins and the trigger group loosened, a very small and short pin fell out of the receiver.

In the image see the pin just above the number "2" on the tape measure.

Can anyone please advise me of where this pin came form? My shotgun seems to function completely without this inside, but I find it hard to believe that this is a spare part...

Thank you for any help!

 

[JonMtl]

It might help to look at the schematic and work by process of elimination: http://www.rem870.com/2016/01/20/remington-870-parts-list-and-schematic/

 

[madashell]

... or you might have a free spare part courtesy of Remington.

Was there anything rattling around in there before ?

 

[skoal]

Never mind I can see it in your trigger group

 

[Hank44]

extractor plunger?

 

[JonMtl]

My guess is that it's the sear pin.

 

[LocutusOfBorg]

I thought that I heard something rattling around in the pistol grip/end of the receiver when I was tapping out the pins holding the trigger group in... But I cannot seem to find where it came from.
Is it possible it fell out of the recoil absorbing pistol grip? I was under the impression that it was just some springs under tension.

The extractor works, I loaded up a bunch of empty hulls with kleenex and crimped them in my Lee Load All, so I could try the cycling of the weapon.
It seems to work fine, but I'm really bothered that this fell out. I've looked at the parts lists and schematics for the gun, but I cannot for the life if me even identify this part.
Is there anything like this in the gun that just generally sits under pressure with the pins in, but could fall out once the trigger assembly is loose?
It's a goddamn mystery to me.

 

[JonMtl]

When I took out my trigger group to install the side-saddle nothing fell out like that!

 

[LocutusOfBorg]

The sear spring seems to be in place. There doesn't seem to be anywhere that is missing a part.

 

[JonMtl]

It really does look like the sear pin.

It's hard to tell in the pic, it probably slides into a hole on the opposite side (left side).

 

[LocutusOfBorg]

It unfortunately is not the sear pin, it is a millimeter or two shorter than the sear pin actually.
Here are a couple of more pictures of the trigger assembly:

Let me know if any of you fine folks see where this couple have sprung from?

Thank you!