Any of the large frame shrouds will go on the mdl 40 (with some work) The 357 mag is a small frame. If you found a 6" HEAVY shroud only for a 357 MAX or 41 mag and up, you could make it work ( your caliber may be marked wrong though). If it is not a Super Mag shroud you will need to lengthen the ejector rod channel in the shroud. A brave preson could do it in a drill press, but a mill makes life alot easier.