Hoppes #9
Works just fine, and no boiling water unless you just have to.
Hoppe's No. 9 cannot and will not dissolve potassium chloride salts. Something that is properly advertised as being able to displace moisture is just not going to do that.
It will remove powder residue, lead fouling, and copper alloy jacket fouling. To the extent that it also displaces moisture, it may
retard the corrosion process, and to the extent that it takes out powder residue, some of the corrosive priming compounds may happen to be shoved out on the same patches. However, I would not rely on that. All of the authoritative literature available when I was young said that it was not suitable for cleaning out corrosive residue because salts are not soluble in Hoppe's No. 9 (or in Outers or Winchester solvents, for that matter).
Hoppe's No 9 came out about the same time that Julian Hatcher (later Major General Hatcher) was brewing his bore cleaners, and Col. Townsend Whelen was trying different mixtures. Their objectives were the same: to clean bores that had been fouled by bullets with jackets made of copper-nickel alloys, fired at almost two and a half times the speed of sound from high intensity smokeless cartridges. That fouling had been identified as a major problem in the then new rifles. I read recently that at the range, some people in those days tried lubricating the bullets with a product made by Mobil to prevent the buildup of metal in the bore.
Corrosion was also a problem, but the cause was not evidently widely understood initially. In some early publications, people opined that the smokeless powder residue was itself corrosive. Some people thought the problem was acid. Of course, we know now that it was the electrolytes left from the priming compound.
So, why was bore corrosion now such a problem? Well, anyone who has fired, for example, a .45-70 with black powder (that's what Julian Hatcher, Frank Hoppe, and Townsend Whelen had been using, along with the rest of the Army) will realize that (1) using the same amount of priming compound with a powder that left far more residue than did the later smokeless propellants resulted in a far lower concentration of corrosive salts in the residue mixture in the barrel and (2) one ultimately had to get all that residue out of the barrel, and the only practical way was to use water. Corrosion had not been a great concern. Replacing the black powder with a relatively clean burning smokeless propellant changed all that.
So, they now needed to get rid of the salts and clean out that pesky bullet jacket fouling, hence the need for new solvents.
Later bullet jacket alloys significantly reduced the problem of bullet fouling.
Of course, the change to non-corrosive priming compounds eliminated the problem of electrolytes accelerating the oxidation of barrels and eliminated the need to dissolve those salts.
I acquired a rather substantial number of corrosive Frankfort Arsenal FA70 primers about fifty years ago from a guy who was moving whose moving company would not transport explosives. I wrote the
American Rifleman about them, and receved a reply saying that they were extremely stable but that I should clean the bore with water after firing them. I kept them in reserve but I never used them, just to aboid the hassle.
I seem to recall that the letter was signed by Julian S. Hatcher, but I could be wrong.
