Hand-wound coil in Colpitts oscillator

Friends and Colleagues, Hi again!
Here is a Colpitts oscillator scheme I'm experimenting with:
https://tinyurl.com/2yq9754k (simulation, NPN with common-base I suppose)
I wound a coil from some length of wire I had at hand - and it has the
following parameters:
diameter - about 32mm,
about 75 turns
wire - 0.3mm
It is wound "heap-style" - so it has only about 6-7 mm "length" and perhaps
about 2mm "thickness".
I measured frequency with oscilloscope (actually, with two different ones)
and it is about 350 kHz, which means that inductance is about 400 uH.
However, calculating by winding parameters over and over by certain
formulas in books and internet I get result twice lower. For example this
calculator
https://www.66pacific.com/calculators/coil-inductance-calculator.aspx
(formula matches with some old book I have at hand) - gives 250 uH.
Questin 1: What may I be missing? perhaps, capacitance between turns? how
can I add this in simulation - should it be capacitor in parallel with the
coil?
Question 2: If I move ferrite core into the coil, frequency reduces perhaps
1.5 times (I tried few different pieces of ferrite found on my desk) -
which at first amused me as I thought inductance is increased hundreds
times. But most probably this doesn't work this way because coil has almost
unidirectional current and the core is saturated by magnetic field?
--
to email me substitute github with gmail please