Bloke denudes his match K31 of its diopter to explain all the funny business going on with the tangent rearsight.

Here's a photo of the B4 target mentioned in the video: https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-xpl1/t31.0-8/13308465_232954337087402_4713610398358302671_o.jpg

And another - the 4 ring is 20cm for scale: https://scontent-ams3-1.xx.fbcdn.net/v/t1.0-0/s480x480/13312751_231649413884561_4240797484083878703_n.jpg?oh=f80beeca5ed3bd803b3555926889f80b&oe=57D460E3