Cleaning rust inside upper

[AwesomeScreenName]

Hello!

I recently received a 7.62 AR upper receiver. It's a nice one but it's clearly been sitting forever as there is a layer of rust aaaaall down the bore. It's a nice thick coating. I have a 30 cal brass brush and hoppes, but I was just wondering if I could soak it in white vinegar for a while to make the cleaning easier. I know the barrel would be fine but I'm mainly thinking of the gas tube. I don't want to clog it up or eat away at it or anything. I'm assuming it's fine but wanted to check with yall first to make sure I'm not being an idjit.
Thanks!

 

[dcloco]

Kroil would be a good first step. Dribble lots, brush, plug bore, and fill to let soak.

Or automatic transmission fluid. Or, diesel...but diesel can leave a smell.

 

[Zahn]

White vinegar will attack aluminum. You will need to disassemble the upper. That's not to say the barrel is fine, but the vinegar will react with the iron oxide. The bubbling is the oxygen being released and the iron will precipitate to the bottom. Depending on the severity of the rust you might have pitting in the bore.

 

[Nodakdad]

Possible corrosive ammo fired and not cleaned properly. I would clean it with a brush and some water based cleaner to flush out any salts. Then go at it with standard cleaners, would start with the mild stuff before moving to anything too aggressive. Could be just "surface rust" or could end up pitted depending on how heavy it was.