U.S. Citizens Also Holding Russian Passports: If you are a dual U.S./Russian national, you are expected to enter and depart both Russia and the United States carrying the passport of that country. If you are a Russian citizen carrying a Russian passport, you should confirm that your Russian passport is valid beyond your planned departure; you will not be permitted to depart Russia with an expired Russian passport, and obtaining one in Russia, as a non-resident, is extremely difficult.
Russian external (international) passports extended by Russian consulates or embassies overseas are not considered valid for departure from Russia no matter how long the extension. Bearers of such passports must apply for a new passport in Russia. Males of conscript age (18 - 27 years old) who are deemed to be Russian citizens may experience problems if they have not satisfied their military service requirement.
http://travel.state.gov/travel/cis_p...y_requirements
Information on how to give up your citizenship is here:
http://www.russianembassy.org/Embass...zhdanstva.html
Only in Russian, sorry!
Personally, I would not try to return to Russia being of military age without renouncing your citizenship. Maybe others haven't had problems, but do you want to risk spending the time in the army to see if you're not going to have problems too?