Question on the finish on my '03

I bought this #996xxx, SA 10-18 barrel back in 2003. Doesn't seem to be a Greek return.
Was changing the stock today and noticed (for the first time) the barrel seems to have a matte finish under the handguards and front barrel band, but shiny like the receiver else where. doesnt look like paint. Was just curious as to why the different finishes.
https://www.milsurps.com/images/impo...100_0382-1.jpg
https://www.milsurps.com/images/impo...100_0381-1.jpg
https://www.milsurps.com/images/impo...100_0379-1.jpg
https://www.milsurps.com/images/impo...100_0378-1.jpg
https://www.milsurps.com/images/impo...100_0376-1.jpg
https://www.milsurps.com/images/impo...100_0383-1.jpg

If that isn't some type of dried sprayed on oil it must be rust. Looks like the rifle was stored in a place where there were big temperature swings causing the rifle to attract condensation and rust.
The area under the front band looks like something was sprayed on it, but the pictures of the rear sight look very rusty.

The rust color is the from the photo and flash, reflecting off some oil I think. Doesn't look that way in person

Try making some pictures without the flash, and how about a close-up of the back sight.

If it isn't rust, & it isn't dried oil, it might be some kind of lacquer. I'd try acetone & a nylon brush on it.

In the past, some people have used motor oil on their rifles. It was whatever came to hand. Oil is oil right? It will dry and give you exactly the result you have there. If that's it, no harm done just do like Neal says and all will be well too.

Sunburn?

I would submit that the metal finish has been treated with some type of varnish or wood finish. It is entirely conceivable that, over time, the rifle was wiped down with an oily material like linseed oil or a light varnish like furniture polish. Some polishing oil has a distinct reddish color but repeatedly applying linseed oil could also produce such as result.

If I might inquire, what was the stock like that you removed? Heavily coated with finish and smooth?

The original stock was a beat up scant stock if I recall. I replaced it with a new one from Dupage a few years ago and linseed oiled it like crazy. There is no reddish tint in person, just when photographed.

Try taking the rifle outside on a "high cloudy" day or in some light shade and taking some more pictures. DON'T use a flash. Pictures taken inside and with flash often distort the color and/or finish of the rifle.