Blue Plastic-Like Residue Seen in Borescope

[Bidwell]

Hi, got a borescope and started looking at my rifle today. I noticed right away that there's this blue plastic-like residue near the crown. No where else. I use Barnes TTSX 130 grain 308 projectiles with the dark blue polymer tip. Is this what that's from? I've read that these tips don't melt so not sure what's going on. Getting good accuracy so it doesn't seem to be effecting much but would just like to know for sure what it is. I attached an image, any ideas?

 

[fuzzymarindave]

I’d guess it was oxidized copper

 

[Ucsdryder]

Copper fouling?

 

[Erict]

Copper - like the stuff your bullets are made out of.

 

[AZ_Hunter]

Copper oxidizes blue. Look at an old crusty penny or copper piping… also why patches with copper solvent will come out blue.

 

[Bidwell]

Copper oxidizes blue. Look at an old crusty penny or copper piping… also why patches with copper solvent will come out blue.

Wow, well that thought definitely crossed my mind. Just was surprised how crusty and plastic like it looked. Must be it. Here's another picture just from my phone

 

[AZ_Hunter]

You should see what forms on my high volume AR suppressor adapters. Blue chunks.

 

[Bidwell]

You should see what forms on my high volume AR suppressor adapters. Blue chunks.

Interesting! First time I've noticed this.