You appear to have a vacumatic nib in the Challenger. I have performed this upgrade once, when a friend broke her original nib, and I had a small 1940s Vacumatic that had been "fixed" with glue and so was unrestorable.
It appears to be the same nib as in the other Deluxe Challenger that I own as well as a Deb Challenger Deluxe I just got last week . Why do you think it is a Vac nib ? Both of the others are also button fillers .
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