Holosun 503 circle/dot on my 1301T with Aridus mount.
The 65MOA circle makes for really quick acquisition and is about the size of 00 Buck pattern at 30yrd
I'm running a Holosun HS510C on my Versa Max open/unlimited gun (3-gun rig). I find just about every optic you mount on a shotgun is way too high (Not a fan of a chin weld, especially on a shotgun), so I made a custom mounting plate and took off the pic rail adapter.
The 2MOA center dot is great for slugs, the 65MOA ring works well enough for shot, and the window is big enough that you can still see some stuff.