If your needs are not simple and you actually have to re-order "every" vert's order to match another model whose vertex size is the same ( and is essentially the same model. Tho I suppose the following is valid for any "UV matchable area" ) Chances are you have committed to UV layouts already and have turned on the…
Overall, looks good. Only crit, is since you've added some plausible subtle wear over various metal parts (BTW nice touch) but not those polymer/plastic bits, especially the perforated barrel jacket albeit heat-shield?! It's designed for SF work, so highly likely there'll be noticeable discoloration and a few hard surface…