Years ago I remember reading on the label of Hoppe's #9 that you could soak the bore with the product and let it sit for 2-3 days to remove fouling from "expansion cracks." That instruction no longer appears on the label. Also, the MSDS list ammonium hydroxide as an ingredient at 1-5%. (Hoppe's #9 Bench Rest is shown at 3-7% ammonium hydroxide). I've also read that "ammonia" can damage a bore.
Out of laziness I have often just swabbed a bore with #9 after shooting and left the gun sit muzzle down for several days -- or even weeks sometimes. So, am I potentially damaging barrels with this practice? Thanks in advance.
