I just purchased a new SUB-2000 and I don’t know what type of ammo they use to proof test these firearms but it was very dirty and it was as if it has dried Cosmoline in the barrel. Wire brushed it then applied Hoppe’s and let sit overnight. Ran a dry patch through it and came out black. Applied JBbore paste several times and then Hoppe’s again overnight. It is finally coming clean. You could see the stuff in the barrel.
Looking forward to doing some upgrades to this rifle. MC