There’s J frames that are Square and round, from my reading the square are a bit older, and current production is round. Hogue sells great grips for either butt style, they’re inexpensive, a bit larger so you wont have a dangling pinkie, and are super easy to install. I’m sure you can contact SW give them the serial number and they can give you all the info you need from production date to the approved ammo. I’d be curious how far back +P ammo has been in production, J frames go back to 1957 I think. The Higher pressure ammo started in the 70s I think. But I’d want to know what’s safe to shoot.