What is this?

[silverado31794]

Helping a guy from work work on a Hatfield sas 12 gauge. Went to pull it apart and this fell on the floor .Don't know what it is or where it goes .can't find a diagram of the parts anywhere.

 

[Tazz]

Try this site:
https://www.gunpartscorp.com

 

[MuleShoe]

Looks like guide for spring!

 

[silverado31794]

Sent pic to the company the said it was a carrier dog plunger