It is important to keep the insides of your barrels unharmed after processing in anything corrosive (Like if it is likely to ever be shot, since damage will increase fouling) should be plugged. Below are reusable plugs that will stand up to heat, acid, and caustic solutions for every size of handgun, rifle, shotgun, and musket barrel to cover everything?
There is even a "sub-caliber" (too small for any firearm .17 caliber and up) plug if there are any small openings you want to keep the hot Parkerizing solutions from leaking into the barrel.
Shown below are the smallest first to the largest last, with the not-so-good multi-purpose (long) in between.
Keep in mind the order button is below the description, not above it, and the chamber plug must be either one size bigger, or two sizes bigger for the .300 necked-down to mid-caliber cartridge. Thanks.