A ferrule is NOT a reliable or permanent crimp device for your application. The metal walls are far too thin.
Try it: crimp two resistors in a ferrule. Bend them at right-angles to each other and try to spin them inside the ferrule. You will find that they spin quite freely.
What DOES work reliably is the barrel from a standard non-insulated crimp terminal. Find a crimp terminal that both wire fit inside and cut the terminal portion away from the barrel. Put both wires inside the barrel and crimp with a proper crimp tool.
This makes a permanent, gas-tight connection that will last for decades.
FWIW - my preferred crimp style for non-insulated barrels of this type is known as a "W" crimp - so-called because of the "W" shape left in the barrel after crimping. The AMP Certi-Lok tool with the "W" crimp die-set is one popular choice.
Almost as good is the T&B "StaKon" crimp tool that electricians use - the small crimp nest works well for barrels up to 16 AWG, the large crimp nest works up to 10 AWG.
Finally, if you don't have any non-insulated crimp terminals handy, just remove the plastic insulation from insulated terminals. The barrel is pretty much exactly the same as the non-insulated terminal.