Mikey:
It was developed specifically to give good ballistics within the pressure limitations of a Contender. It's a rimmed cartridge based on the 225 Winchester (it's just a fireformed and necked up 225).
It was popularized and made proprietary by JD Jones (i.e., "JDJ") of SSK industries. It is his the most popular of his many cartridges. The other two cartridges he is best known for is the 375 JDJ, which is for taking large game with .375 caliber bullets, and the 309JDJ, which is a deer cartridge that shoots .308 bullets. Both of these cartridges are based on the necked down 444 Marlin case. They are also specifically designed for use in the Contender.
It shoots a 120 grain bullet at 2300 to 2400 fps from a 14" Contender barrel. That's pretty darned good for a Contender.
The available bullets for the 6.5 are very compatible with the 6.5JDJ because most of them were developed for the relatively low velocity of the 6.5 Swede.
Since the Encore was released it has become obsolete, except to those cranks among us (me included) who like the smaller and lighter Contender rather than the Encore.
The 6.5JDJ has no practical value in guns other than the Contender. Other cartridges are better.
As to results, it sure is deadly, and it has light recoil for a bonafide hand cannon-- about the same as a light-but-not-powderpuff 44 magnum load.
Barrels and dies are only available new through SSK.