What you have left after the stripping process is just a wire with a
thick insulating jacket... The fact that it was part of a coaxial
cable before the stripping has no more bearing on the answer than the
fact that the copper was previously greenish ore nodules buried in the
ground and the jacket was made from nasty smelling crude oil...

So, forget all about 'coax', it has nothing to do with the question...
If your new wire had a jacket of the usual thickness then the loss of
velocity factor would be on the order of 3% compared to the usual 983/F
or 300/F... Given that it is a thick jacket I would guess the VF to be
down by 5%... So take what ever formula you are working with to
determine antenna length and reduce that length by 5% for cutting your
wire to resonance...

denny / k8do