I don't know why its that wide either....maybe its ok / maybe not ....but I don't think this is something we can help you evaluate over the internet either.
You might ask around at your local range...see if there is someone in your area that is experienced with S&W revolvers.../ but that scorching and carbon buildup around the forcing cone, is an indication to me, the gun hasn't been that well cared for.
Is the timing tight ...or is it a little suspect too ? Check out the revolver link in detail - on how to check a revolver - if you haven't done that...it'll give you a lot more detail.
and good luck - whatever you decide.