LCR meter and iron core inductors
A simple LCR meter will not give accurate measurements if the core is very lossy. 

It it's truly an iron core (not iron powder) then the eddy current losses will be significant- like a resistor in parallel with the coil. That translates to a lower impedance which the LCR meter will interpret as a lower inductance since it is not measuring the phase angle of the result. Iron powder is also lossy.

An LCR bridge would sort this out for you (and show you the equivalent parallel resistance as well as the inductance), but the bottom line is that your core is going to be way too lossy to use at RF frequencies and you should use a ferrite core or air core that is suitable for RF.