The Contender is available in a .45 cal ml'er but it is in a "carbine" configuration, not a pistiol. If you were interested in a pistol you would have to get the Encore frame.

Specifications:
Caliber: .50
Ignition: 209 Shotgun Primer (Closed Breech).
Barrel Length: 15".
Rifling Twist: 1 in 28" twist for use with Sabots and Conicals.
O/A Length: 20 1/2".
Approx. Wt: 4 lb.
Sights: Click adjustable steel rear sight and ramp style front sight.
Grip: Solid American Walnut Grip and Forend.
Extra Features: Interchangeable barrels offered as accessories. The centerfire pistol barrels listed at the Encore Pistol section of this site interchange easily with the muzzleloading barrel. Drilled and tapped for scope mounts.
Loading: Accepts Magnum charges of up to 110 grains of FFG Black Powder or Pyrodex® equivalent (or 2 Pyrodex® 50 caliber, 50 grain Pellets).