Home made Ferrite Core inductor

I bought some cheap ferrite pot cores from Bulgaria (via eBay).

They have 2 part ferrite and a plastic bobbin.

I hoped to get up to 500mH from them in order to use them on guitar effects pedals but on first attempt only got 218mH... Still that's a pretty huge inductance!

Hopefully I'll get chance to build a Wah pedal in the future, when I can source a cheap enough enclosure.