Model 10?

I recently came into a Smith Model 10 with adjustable sights. I was just told that the adjustable sights make it a model 15.

I think it's from the 50's. The butt has a "K" stamped on it, and the serial number 2880xx, and the numbers 76130 under the cylinder. There is also an "X" stamped on the bottom of the barrel.

What do I have and when was it built?

Thanks in advance for the info!!