If you are on probation for a misdemeanor charge in the state of Ohio, and you have a hand gun in your possession, how much trouble will you be in?

Your probation could be revoked and you could be sentenced to whatever the sentence would have been if you had NOT accepted probation. Plus you would face the hand gun possession charge -

If you are on probation for a misdemeanor charge in the state of Ohio, and you have a hand gun in your possession, how much trouble will you be in?

Do your conditions of probation say anything about firearms?

I have mssed it, but I don't see any Ohio laws prohibiting someone convicted of a misdemeanor from possessing firearms.

"2923.13 Having weapons while under disability.
(A) Unless relieved from disability as provided in section 2923.14 of the Revised Code, no person shall knowingly acquire, have, carry, or use any firearm or dangerous ordnance, if any of the following apply:
(1) The person is a fugitive from justice.
(2) The person is under indictment for or has been convicted of any felony offense of violence or has been adjudicated a delinquent child for the commission of an offense that, if committed by an adult, would have been a felony offense of violence.
(3) The person is under indictment for or has been convicted of any felony offense involving the illegal possession, use, sale, administration, distribution, or trafficking in any drug of abuse or has been adjudicated a delinquent child for the commission of an offense that, if committed by an adult, would have been a felony offense involving the illegal possession, use, sale, administration, distribution, or trafficking in any drug of abuse.
...(B) Whoever violates this section is guilty of having weapons while under disability, a felony of the third degree."

I know that a misdemeanant in possession of a firearm isn't a crime under Federal law.

There is nothing I can read that does not allow a person with a misdemeanor from having a hand gun ( a person with a felony can not)

Did your probation say something about handgun?

If you are on probation for a misdemeanor charge in the state of Ohio, and you have a hand gun in your possession, how much trouble will you be in?

Could you please extrapolate what you meant by "and you have a hand gun in your posession"? Were you stopped by the police and had this gun in your possession? Is that it?