I got one of the bad 696's when they first came out.
I thought it was a by-product of the chemical rifling process they were trying, or a forcing cone issue - but it was the least accurate Smith and Wesson revolver I've ever owned. And would lead up horribly. It's possible that in reality it was the afore-mentioned barrel constriction. Sent it back to S&W, who re-cut the crown.
Can't remember if it fixed the accuracy or not. I was relieved to get my money back out of it and am now amazed at the current popularity of these things on the Internet.
Smith needs to re-issue this. Fantastic concept that was poorly implemented.