I am going to buy a Glock 35 Gen 4 and was planning to put an aftermarket 9mm barrel in it for competitive shooting. Would that disqualify it for any stock classes? What if I put a threaded barrel in it that makes the barrel a little longer? What's the difference between Iron Sight & Production Class? I am guessing Production Class is more restrictive? I would like to hear what if anything is allowed to be done to the firearms in these two classes. Basically I am interested in shooting in classes that do not allow comps or optics and am trying to figure out what these classes are and what is allowed.