I’m thinking Bendutro has the JR model 500 Smith, which does have a 1:10 twist. I also have the JR model. I haven’t messed with the 700 grain but I have with the 600 and @ 1,160fps the recoil isn’t all that bad – a tad less felt recoil than a 500 grain @ 1,300fps. I would think if you pushed to 1,300fps and beyond it would be a wakeup call. Haven’t seen a need to go there yet with 600 grains.
For those with the JR model – I sent mine back to S&W, as the cylinder would bind occasionally. Smith advised the problem was with the barrel and they returned it with a cylinder gap set at 0.007. They stated I would not experience that problem again with a cylinder gap of 0.006/0.007. I haven’t noticed any difference in velocity/accuracy with the larger gap. I know of two other JR models that experienced the same problem after a couple thousand rounds and Smith returned those revolvers with 0.006/0.007 cylinder gaps and the revolvers aren’t any different relative to accuracy.