Picatiny rings doesn't fit smith&wesson 500 picatiny rail - Volquartsen Firearms Nova Scope Rings

I have a Smith & Wesson 500 mag model 170231 with the 10.5 inch barrel. This model has a barrel shroud with a milled in picatiny rail. Supposidy according to volquartsen these mounts are mill spec for a picatiny rail. Soooo I called up Smith & Wesson and asked them what rail was milled into the barrel shroud. They informed me it as also a picatiny rail to mill spec. Just being pessimistic I called back both company's three different times and was told the same answer over and over. So who's measurements are off? For the quality they look solid and for a quick fix i can do a little filing on the rings to make em work. Although I shouldn't have to. Overall can't give them a proper full review just because I havent used them.