EDIT: Duratrax - the MC-59 is classified as a hot plug but is designed to run with wider ranges of nitro which makes it a good equiv. for an OS 8, see link below.
Originally Posted by sheveman
... I am running 30% fuel, that is what the guy i got from told me to use
The three most common causes of blowing plugs regularly are running too lean, too high of compression, or improper plug temp for the nitro percentage you're using (forsaking engine break-in's.) If your temps are accurate, it's not likely it's too lean. Running rich usually doesn't burn out plugs but it can.
Generally you pair the plug temp range with the nitro percentage you're using: high nitro=cold plug, low nitro=hot plug, with 20% being "medium." The plug temp changes the ignition point of the engine, much like altering timing on a full-scale. Your MC-8 should be right on for that being cool to medium with 30%, but you could try an MC 9 or OS 5. Additionally a cold plug will outlast a hot one due to the thicker element.
If all lese fails you could **try** a hotter plug just to see how it fares, if you bought it used maybe someone's fiddled with the head clearance.
Good page on plug temps