Barrel Corrosion?

[rod5591]

I bought a used "upper" for an AR-15 style rifle. Former owner is deceased. It was a Colt 20 inch barrel. C MP 5.56 Nato 1/7 HBAR. I went and built a lower around it. Haven’t fired it yet.

When I was cleaning the bore with a brush noticed a spot 2/3 up the barrel where there was resistance. The rest of the barrel is smooth, but in this one spot over and over these is resistance, not enough to stop the brush or come close to stopping it, but enough to notice. I tried looking down the barrel but it is too dark to see anything.

Any thoughts? Safe to fire?

[Jim Watson]

You aren't rubbing the gas port, are you?

[KodiakBeer]

I tried looking down the barrel but it is too dark to see anything.

Use a light?

[jonmerritt]

sounds like the gas port.

[rod5591]

It wasn't anything I guess, since this gun shoots like a dream now.