This is an update of a post I made about 20 months ago in this gunwriter's forum.

The original formulations of Hoppe's No. 9 from about a century ago contained nitrobenzene as one of the solvents. It had an odor the chemists call "almond-like". Certainly the odor of Hoppe's changed when the nitrobenzene was eliminated (in the 1960s?). The change is pretty obvious if you can find an old bottle to sniff alongside a current bottle. I don't know whether the change occurred when the original Philadelphia company was bought out by Penguin Industries of Coatesville, PA. Don't inhale the earlier product too deeply, because nitrobenzene can cause real respiratory problems by messing with your blood hemoglobin. As noted above, it's also carcinogenic to humans.

No. 9 is made and bottled in by Tri Pak Inc (www.tri-pak.us), in Vandalia in south-westeren Michigan. Hoppe's is a part of Bushnell, with main offices in Overland Park, Kansas.

The current MSDS posted on hoppes.com is dated 2012. The listed components are:
  • Ethanol
  • Kerosine
  • Oleic Acid
  • Amyl Acetate
  • Ammonium Hydroxide
The MSDS dated 2010 had the same list, except that the first listed ingredient used the alternate and more common spelling "kerosene".

The oleic acid almost certainly reacts quickly with the ammonium hydroxide, producing ammonium oleate, which is a common component of many household soaps and cleaners. The ammonium ion reacts with copper fouling to produce the greenish goo that can be patched out of the barrel. I recall having read that earlier formulations used ammonium stearate. Both are 18-carbon compounds, with the oleate being a mono-unsaturated carboxylic ion, and the stearate being saturated. Both are somewhat soluble in kerosene. I've observed the ammonium salts precipitating in Hoppe's Benchrest No. 9 when my basement cleaning area gets chilly. I presume the Benchrest product has in it the maxium dissolvable amount of the ammonium compound.

Amyl acetate is banana oil, and combined with the kerosene constitutes much of the familiar Hoppe's odor, as noted in a post above,.

In 2003, when Hoppe's was made in Idaho by Michael's of Oregon, the MSDS showed some secret ingredients:
  • Ethyl Alcohol
  • Kerosene
  • Trade Secret Ingredient(s)
  • Organic Ester Trade Secret
  • Ammonia, aqueous
Whether the more recent forumulation of Hoppe's No. 9 is as effective as those that preceded it is an open question. Nothing in it will harm steel, unlike the solvents that contain aqueous ammonia.
--Bob