https://imgur.com/a/ZaceuuY
Here is the 45 beside a Gecado/Original 25
The cylinder is shorter on the 45 and the gun overall looks a similar size.
I purchased these 2 rifles together and these are the photo’s sent by the seller.
Geezer I think your spot on with where this gun lies in the in the BSF line up. Spec’s for the 45 are also only for .177 so probably only produced in that caliber because of its power limitations I guess.

The catalog is pretty hopeless in terms of properly describing the different models! Could be another reason BSF are gone.