Despite what you have been told about not being able to own a firearm, after being convicted of a crime that is defined as "Domestic Assault" Title 18, the U.S. Code that governs that specific act in regards to posessing a firearm is pretty clear on the subject.
Unless there are state specific laws that apply, a person can, under certain conditions, have been convicted of a crime of "Domestic assault and still legally own a firearm.
Relevant portion of Title 18 as it applies to eceptions;
Except as provided in subparagraph (C), the term ''misdemeanor crime of domestic violence'' means an offense that - is a misdemeanor under Federal or State law
A person shall not be considered to have been convicted of such an offense for purposes of this chapter, unless - the person was represented by counsel in the case, or knowingly and intelligently waived the right to counsel in the case and; in the case of a prosecution for an offense described in this paragraph for which a person was entitled to a jury trial in the jurisdiction in which the case was tried, either the case was tried by a jury, or the person knowingly and intelligently waived the right to have the case tried by a jury, by guilty plea or otherwise.
If a person was represented by a lawyer then they are considered to be convicted, like wise if the accused knowingly and intellegently waives the right to councel and or trial by jury.
Case law already exists on this matter and can be found in the 9th Circuit Court Opinion on USA v Akins. There are other cases, but this seems to be the most comprehensive one for determining what does or does not constitute a knowingly and intellegent waiver of the right to counsel.
The short of Akins is this; He was convicted of domestic assault, after he signed a waiver to right of counsel. Some years later he was arrested for posessing a firearm. The lower court found him guilty. Akins appealed on the grounds that he did not knowingly and intellegently waive his right to counsel. The 9th Circuit Court agreed with him and reversed his conviction
The moral to this story is; That if you or someone you know was fastracked (read Railroaded) through the system because it was a "petty misdemeanor" and you were not properly informed of your rights and you did not willfully or knowledgeably waive them, then you can still own a firearm.