I am assuming, based upon the fact you did a 120, that you received an SES ("suspended execution of sentence") and were, therefore, convicted of a felony. If you were convicted of a felony, you are forever barred from possessing a firearm. If you plead guilty and received an SIS, you are permitted to own a firearm in Missouri, but you are not eligible for a concealed carry permit.
Pursuant to §571.070 RSMo., it is a Class C Felony to possess a firearm if you have been convicted of a felony.
See this recent article on the topic from the Riverfront Times:
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