iron core inductor calculation

It depends...... if you need an accurate 6 Henries then no, its not good enough.

But if you need a rough idea then yes its fine.

Remember the waveform of the second reading will be grossly in error due to the core being in.... hold on I might be wrong. I would have stuck an oscilloscope on it though to see if the waveform you are measuring is causing an error.

I also wouldn't have used the full voltage rating on the coil as if it is meant to only have 22 mA plus a bit for a load, flowing then the wire will self heat causing errors, when using a higher current.

Why didn't you just put and ac load on the output and adjust it to give your primary inductance?

Cutting through laminations sounds a right pain.