Sixpack from www.bellmtcs.com :
Basic Differences
Frame Sizes: Encore is bigger than G2 or Contender,
Barrel diameters where they seat in the frame: Contender/G2 13/16," Encore 1" so they do not interchange, thus,
Scope Bases: Encores have the larger radius on the bottom,
Internal mechanism: Contender has a hammer block, Encore and G2 sears lock the hammer at half cock,
Trigger Mechanisms: Two different types of Contender trigger groups both of which are removeable while Encore and G2 trigger mechanisms are not removeable,
Firing Pins: Encore is center fire only, Contender and G2 have a selector on the hammer to fire either centerfire or rimfire,
Hinge Pin Hole Diameters: Encore is 7/16" (.4375"), and Contender and G2 are 3/8" (.375"),
Internal Frame Mechanism Springs: No Springs in the Contender frame interchange with Encores & G2s,
Forend Screws: Contenders & G2s use No. 10x32, and Encores use No. 8x40 screws,
Hammer Extensions: Two different sizes for Contenders--vintage with the selector lever on top of the hammer is the same size as on Encore and G2,
Dry Firing: Encores and G2s should not be dry fired unless the firing pin bushing is removed and the fall of the hammer cushioned while Contenders can be dry fired continuously with no harm at all to the frame SO LONG AS THE HAMMER IS NOT COCKED (Dry firing simply releases the striker in the trigger group and gives the full effect of the trigger pull, independent of the hammer being cocked. Opening and closing the barrel resets the striker),
Forend Screw Hole Spacing: Hole spacings for handgun barrels is different carbine hole spacings in both Contender/G2 barrels and Encore barrels.
Grips/Buttstocks: Contenders, G2s, and Encores all take different grips, buttstocks, and forends.
The Encore action is almost a pound heavier than a Contender. The G2 Contender has stiffening bars on the side of the frame at the top like a Winchester 94 Big Bore. The original Contender has smooth sides. Much more info at Bellm's website.