Welcome to the forums! Glad to have you here! 
I'm thinking the buildup in the barrel is most likely copper. How many rounds do you have through it? Probably the cleaning you did exposed the copper so you could then see it. Copper fouling can easily be mistaken for rust... kinda orangeish.
For copper removal you can try either of these two products:
I personally use the Sweet's 7.62 and when you follow the directions on the bottle, (wet a patch with Sweet's and basically swab the barrel for 60 second intervals) it will work quite well. IF you have copper fouling, the patches will come out a light blue color. Keep giving it "treatments" until it's all gone or as much as you can get out of it.
For just general light rust, I think Hoppies No. 9 would work... probably any solvent really would work to remove light rust. I wouldn't use Sweet's just for rust because it has a strong ammonia smell!
Let us know what you find out, whether it's copper or rust.
I'm thinking the buildup in the barrel is most likely copper. How many rounds do you have through it? Probably the cleaning you did exposed the copper so you could then see it. Copper fouling can easily be mistaken for rust... kinda orangeish.
For copper removal you can try either of these two products:
- Sweet's 7.62[/*]
- Barnes CR-10 (another forum member recommends this stuff)[/*]
I personally use the Sweet's 7.62 and when you follow the directions on the bottle, (wet a patch with Sweet's and basically swab the barrel for 60 second intervals) it will work quite well. IF you have copper fouling, the patches will come out a light blue color. Keep giving it "treatments" until it's all gone or as much as you can get out of it.
For just general light rust, I think Hoppies No. 9 would work... probably any solvent really would work to remove light rust. I wouldn't use Sweet's just for rust because it has a strong ammonia smell!
Let us know what you find out, whether it's copper or rust.
