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I own both.
They are both excellent imo.
imo as to best possible accuracy, I would say the VIS more ridgid & slightly heavier.
When your talking SPR & sub MOA accuracy the slightest barrel harmonics/recoil impluse may make a difference in terms of a surgical shot.
YMMV...
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I can't speak of the VIS as I don't have one, but the Noveske/SWS rail is very narrow, is pinned internally to the upper receiver for anti rotation, and it has multiple QD swivel sockets. The VIS doesn't have the QD swivel sockets.
I'm very impressed with the SWS/Noveske rail on my N4 low profile.
http://noveskerifleworks.com/imimg/swsmur_2d.jpg
http://noveskerifleworks.com/imimg/swsmur_5d.jpg
http://noveskerifleworks.com/imimg/swsmur_6d.jpg
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My SWS rail is solid and well made, but I wouldn't call it lightweight. That barrel nut is 5 oz alone. My 11" rail - including the barrel nut - weighs in at 19oz. It is several ounces heavier than competing rails from LaRue and Daniel Defense.