Take this for what it is worth ... remember you read it on the internet.
I believe that in the massive Vudoo Repeater sticky thread there is some info on the evolution of the Vudoo repeater breech face. The latest version, which you have, is designed so that some of the crud that comes with shooting suppressed has a place to accumulate between cleanings without affecting function.
If I'm wrong here MB will flame me and I'll never post my vague recollections again. Seriously, if you post questions like this in the sticky thread MR. BUSH is on them quick and you get himself providing the definitive lowdown.