The number 28 stamped on various parts - including mag button and cutoff - is important. But what you really want to know is whether you have a 28 ga receiver in your hands, and not a 16/20 that was built into a 28 ga gun using 28 stamped parts.
It's really pretty simple:
http://www.shotgunworld.com/bbs/viewtopic.php?f=60&t=391354I consider the cutoff raceway/shellplate stop more reliable than the 28 stamped on the back of the frame. What does it take to remove about .020" (to preclude ghosting) of metal from a nice flat surface, then restamp a 28? Welding/recutting an internal raceway and welding up and reconfiguring the shellplate stop seems like a whole 'nuther level of difficulty.
Maybe so, never under-estimate the criminal mind- the surface where the original gauge of the receiver was handstamped at the top inside of the rear receiver boss was usually a tad rough- as it was invisible in the assembled gun- and very small area to get a, let us say, Dremel or Do-All grinder with the right stone to do this "trick" you mention. And there were then be a slightly lower surface from this grinding, detectable by indexing a depth gage micrometer from the outer radius and checking the depth all the way around the radius of the inner boss of the receiver rear. Also, all the WRA gauge stamps were made as sets- that is to say- a 12 gauge was a single stamp with a double head- 12, ditto for the 16, 20 and 28- and the tool room was charged with maintaining them as to type face sharpness- so one blow from the assembler's machinists hammer was sufficient to "double stamp" (if I may coin a phrase here) the specific gauge. I am 99% sure I could spot this "counterfeiting" in this area in a New York minute- Oh, a segue perhaps, but FWIW here- I own 2 Model 12 Heavy Duck 3" magnum models- one mfg. in 1939, the other in 1948- I have removed the factory buttstocks on both in the many years I have owned them- they are stamped in identical fashion to my standard 12 gauge Model 12's--
