First, it probably was not outside temperature related, just shooting gets a gun a lot hotter than being outside. Second, I don't believe you can hurt a revolver by "over cleaning" it. That said, there may be firearms that may be affected by over clearing, but not the GP100. I clean my guns every time I take them out no matter how many rounds I put through them and have had no indications that they show any extra wear. In fact, when I was shooting PPC, I would clean my revolver between every stage (as most all the competitors did also) and nothing bad every happened. Third, 250 rounds without cleaning is going to be hard on any gun, especially with cheap ammo. The build up of crud could/will affect pressures and that isn't a real good thing to happen. If you see a lot of crud/lead build up and can't get it all out with your normal cleaning tools and solvent, a Lewis Lead Removal tool is you friend. It will pull out stuff from a barrel/cylinders that looks like they are clean.
Even with what your barrel looks like in the picture, a call to Ruger, as stated above, will probably result in them fixing your revolver at no charge.
Oh, by the way, from the picture, it looks like the rear sight retaining pin is sticking out too far, if it falls out under recoil you could lose your rear sight. If it moves easily, take it out and put a very small bend in the middle of it, that will make it a lot more secure and won't come out under recoil.
