If the Buffalo Bore company says they are getting similar numbers I would be inclined to believe them. The owner of BB knows what he is doing.
This is great. Sounds more or less identical to the BB 38 sp 158 +P LSWCHP I've chronoed. That stuff all got 1100 fps from several different 3" steel framed S&W's I shot it in. Creeping right up on .357 mag with a fraction of the bang and flash.