I did not see it but it came from a reliable friend. The local indoor gun range took in a well worn M&P from the early years I think it was a second change 1905. Since the blue was badly worn and they needed another .38 Special renter it wound up on the rental shelf and digested a lot of commerical reloads for quite a while but one day the cylinder split while firing that commerical reloaded ammo.

I think that it could well be a split cylinder every now and then that caused the the change. In 1909 the cylinder notch shims were eliminated from the double action revolvers and heat treating the cylinders would be a lot cheaper than bringing back the cylinder notch shims.

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Gun Safety is no accident.