10-4 that the .17 Javelina is a bit longer than the Mach IV; the Javelina is a shortened .222 whereas the Mach IV is on the 221 Fireball case necked down. I'm thinking of going to the latter as case forming/prep for the Mach IV is much easier.

I can't find dimensions for the Javelina to get a feel for how far the barrel is going to be set back.

Does anybody have experience doing this rechamber?