can someone tell me what this is and how to safely remove it? I assume its rust that pitted the barrel of my 870 12 gauge. This is my truck gun and used for SD
pitted rust. I would try to clean it out with a brass brush and some gun oil. It's a smoothbore so I wouldn't worry too much about it. If guns are left in trucks, the constant change of temps can lead to condensation, which can lead to rust. They need to be well oiled and checked on every once in a while.
Stop at the hardware store and pick up a 7/16" dowel rod and some 00 steel wool. Cut the dowel to a length that will go from end to end on your barrel. If the dowel is too short you can clean from both ends. Take a pad of steel wool and remove about 1/3 of the pad. Stretch the remaining 2/3 over the end of the dowel. Pull it over the dowel until you have a huge Q-tip with about 4" of steel wool on the dowel. Secure the end of the steel wool with some tape. I used electrical tape. Put the dowel into the barrel and connect it to a cordless drill. Run the drill and move the rod along the length of the barrel. Use your off hand and monitor the heat built up in the barrel. Do not let it get much better than warm. If you have a 2nd dowel, cover the end of that one with a whole pad of steel wool. This one can be used to clean the chamber. These can be re-used. The guy that has this site knows a crap load about the 870. http://www.aiptactical.com/install---cleaning.html
I agree it looks like some minor barrel pitting. Biggest thing is if there is this little there may be more so give it a good look over. Personally i would hit with some Qtips with solevent or other cleaning agent being careful to not spread even the juices around to much until clean. Then i would def do a over all barrel cleaning Ive never seen that! Looks like a awesome idea!
I know this is late, but the big 45 from frontier has been recommended to me by guys who restore antique guns. http://big45metalcleaner.com/