If that Julia rifle is a Vickers, I would think that they ordered a barreled action from Mauser and then added a stock and their provenance. The barrel and action is pure Type A. Mauser made complete rifles for Rigby, to Rigby's spec, in the early days. This is a fact. It would not surprise me if Mauser made the entire rifle for Vickers, but I think it more likely that Mauser just made the barreled action.

The sketch in the Vickers advertisement doesn't exactly match the Julia rifle, but this could be just because the artist didn't make an effort to exactly copy the rifles details. We may never know for sure.