Argo44, thanks for reminding me. That New Zealand gun is a real beauty, and like all 1850s British pinfires, a rare treasure. I've just rambled at length about these early designs in your Reilly thread, so I won't repeat it here!
The original Lefaucheux double-bite fastening system partially raises the barrels when the forward underlever opens fully. This assisted opening would have helped speed up loading and unloading. In the New Zealand Reilly I'm guessing it has the Lang-designed rising stud on the action bar near the face, which moves when the forward underlever is rotated. While a feature of the early single-bite forward-underlever (and some single-bite rearward-underlever) guns, this mechanism was never patented by Lang and it was widely copied.
