You assume he's guilty. He's presumed innocent and should have good legal representation. Instead of jumping to conclusions that he's guilty, try fighting the case.
It depends on to many factors to answer without being on the case. His criminal history, the judge, the plea offer and his actions all go into the sentence. However, Having Weapons Under Disability in violation of ORC 2923.13 is a felony 3, which carries a possible 1 to 5 years in prison. There is no presumption either for or against prison and he could get community control sanctions. Community control sanction used to be called probation and include up to six months in jail.