dartblaster.de have got their hands on a pretty awesome Zombiestrike blaster,the Doublestrike.
It looks like it has the same intelligent AR design like the Roughcut,which delivers air only to the chamber in which the dart is inserted.I think it is a front loading blaster,because breech opening will only complicate the overall design and function.
This certainly reminds me of the Derringer,
Check out their video on the link below
The video also shows the slingfire,which seems to have a slimmer profile than previously thought.