Paul,
The Martini is a switch barrel and the chamberings are .17 HMR and .22 RF Mag.
The action is a Model 12 BSA that Morris profiled like the Model 6 takedown versions. The barrels are 24" long and are full ovate profiled. I have an early Francotte .410 Martini that has a top tang and that was the inspiration for the tang. I'm working on a .25-35 Martini and I scalloped it and it was a nice touch that got incorporated in Morris' rifle.
Some years ago I tried to make a peep sight base for a Martini that used the cleaning rod hole as the attachment point. My base never got completed but during the development of this action Morris ran with the idea. I found windage adjustable Lyman peeps that use a lateral dovetail for adjustment and these got incorporated into Morris' base design saving a big effort in making the entire sight. They sights are readily removable with a few turns of the thumb screw and the only mounting vestige visible when the sight is removed is a small dimple where the thumb screw secures the sight.
