On the two 929 I have sent back to Smith for accuracy issues. One got new Barrel,cylinder,trigger, hammer,rear sight, the other just a barrel. When I asked Smith about the cylinder spec the engineer said .3575" was the spec for the 929 and yes the .38 Super 627's were .356".
As I have 10 k 115 9mm projictiles I am working on a load with them. 160 Bayous work well, .357" 125 gr and 147gr also load and shoot well. All loads tested at 50 yards. Plan to use the 929 in NRA Action Pistol metallic class.
Tom