Can anyone tell me what this is?

Jwhite225

Private
Minuteman
Jan 29, 2021
6
0
Oak Ridge TN
I’ve seen this before in videos but haven’t been able to find out what it is exactly. My guess is that it magnifies the turret to be able to see it better but I’m not sure. 932D60CD-DD1E-4B74-9D7F-A9C4B0872FC2.jpeg