I noticed that as well. It looks like it was removed, not broken. Looks like there is some type of replacement on the rear like a Ghost Ring set up.
That's the only knock I have against my MKII.
The front sight eats holsters. With the undercut to reduce glare and the sharp edge it's hell on holsters, flesh, paint, etc.
On this gun the rear is so high at first I thought it was to account for the new lower front, but that's backwards...it would only raise the impact higher.
Does anyone make a ramp sight for the Ruger MK's similar to a S&W revolver? Cutting off the sharp edge would lower the sight height.
Neat video. In the comments section someone thought they saw 'brass flakes' coming out with the ejection of the spent case. I think it's just unburned powder flakes. Notorious with 22's.