I had N679xxx, an 8-3/8" M25-5 I bought new in early 1980. It was the worst S & W shooter I've owned before or since. The problem with that revolver wasn't the cylinder throats, which at about .454". No problem, since I have .45 molds that drop bullets at that diameter or larger. The problem was the cavernous forcing cone, both too wide and deep. A cast 454424 would drop completely into the forcing cone so that its base was below the end of the barrel. A bullet would be completely unsupported by the cylinder throat before it engaged the rifling. It would shoot jacketed bullets into 4-5" at 25 yards (which to me is poor accuracy), but cast bullets were wild. You can imagine what was happening to cast bullet bases during the trip from from the cylinder to the rifling. Needless to say, leading was very bad in the forcing cone.

I looked at other 25-5s in that same time period and they were all the same. M29's shared the same affliction around the same time.

As an aside, I traded that M25-5 for an HK91. Kind of shows you how times have changed.