2" instead of a 1-7/8" barrel. Chambered in .357 Magnum, so of course it will take that or .38 Special. It’s an all stainless steel gun…so not an airweight. It shoots just fine. I just rarely ever shoot it, in fact it’s been years since the last time, so it’s just taking up space in my safe and I have 2 other .357s so I don’t really rely on having it.
Here’s the S&W page for this model: https://www.smith-wesson.com/product/model-640.