Sorry, Avvo is not for homework.
If it were, your question cannot be answered without knowing why the expert is testifying. E.g. to identify caliber of weapon, powder residue, product liability.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.