Do the normal inspections .. ring the bbls and be sure it is on face by removing the forearm and wiggling it by the bbls to see if any play can be detected. If it meets those tests then the $300 is likely fair. It is unlikely that the gun will not have reasonable proof marks, but you will have to tell us what they are or look at some of Larry Brown's remarks on previous posts to get a better idea of what to look for. Most of the French guns, inclusive of MAC's will have more than adequate proofs as far as pressure goes. That does not mean that you will be comforatble shooting any heavy loads in a typical French shotgun. That is the normal paradox w/French doubleguns .. the guns are well made and carry proofs to prove it, but do not weigh enough to allow use of heavy ammunition. Odds are good that it will have short chambers, but that is not such a big issue. At the risk of being slammed for having done so, I have had Kirk Merrington lenghten the chambers on one of my own French doubles and open the chokes while he was at it, both for my own enjoyment. A MAC could undergo similar conversion if needed and if judged to be safe to do so by a competent g'smith. A MAC or the sort you are describing will not be more than a well made utility gun, but it will prolly be better made & fit than a lot of American 'behind the door' guns as Lord Glenthorne is wont to call them. Hope this helps you out. There are others here who can offer additional and prolly better insight on MAC's, but you said that you needed some input NOW. I have never owned one, but I have examined several over the years. FWIW, none were particularly striking, but all were well enough fit.
