I have made a few thousand 17 fireball and 20 vartarg but I used Redding case forming dies and formed brass for both from LC 223 brass, which was very labor intensive.
I also necked down some Lapua 221 brass to 17 FB using a 20 VT fl die then a 17 FB die but I had to turn the case necks since mine has a custom chamber.
You should be able to just get a Hornady 20 VT FL die probably the cheapest and run the 221 brass thru it then the 17 FB die, Imperial sizing die works good use it very sparingly or Hornady one shot lube it works very well also.