Last year there was a brief discussion here about the
wonderful smell of Hoppe's No.9 firearm cleaner.
Last week I bought a fresh bottle and. after perforating
targets last evening I opened the new bottle this morning.
It's changed! Smells horrible, like a teen boy who just
discovered body spray. Yecchhh.
A quick search shows that others have noticed as well, at
least one of whom is a chemist. In an all to typical story,
the distinctive odor was from nitrobenzine, which is now
disfavored by the EPA.
I found some vintage No.9.
On Sun, 17 May 2026 19:40:37 -0500, AMuzi <am@yellowjersey.org> wrote:
Last year there was a brief discussion here about the
wonderful smell of Hoppe's No.9 firearm cleaner.
Last week I bought a fresh bottle and. after perforating
targets last evening I opened the new bottle this morning.
It's changed! Smells horrible, like a teen boy who just
discovered body spray. Yecchhh.
A quick search shows that others have noticed as well, at
least one of whom is a chemist. In an all to typical story,
the distinctive odor was from nitrobenzine, which is now
disfavored by the EPA.
I found some vintage No.9.
EU version of MSDS Sheet for Hoppe's No. 9 Gun Bore Cleaner: <https://www.copquest.com/knowledgebase/MSDS_Hoppes_No_9_Solvent.pdf>
Ingredient CAS No % WT
1 Kerosene 008008-20-6 15 - 40
2 Ethyl Alcohol 000064-17-5 15 - 40
3 Oleic Acid 000112-80-1 - -
4 Amyl Acetate 000628-63-7 5 - 10
5 Ammonium Hydroxide 001336-21-6 1 - 5
The pleasant odor is Amyl Acetate: <https://www.cdc.gov/niosh/npg/npgd0031.html>
"Colorless liquid with a persistent banana-like odor"
The unpleasant odor might be the use of industrial kerosene instead of de-odorized (low-sulfur) kerosene, which is used for kerosene lamp
oil, kerosene heaters, diesel fuel etc. My guess(tm) is the factory
used the wrong type of kerosene: <https://wintersunchem.com/product/low-odor-based-solvent-deodorized-kerosene/>
You can remove some of the smell with activated charcoal filtering,
but I don't know what it might do to its gun bore cleaning abilities. <https://zenodo.org/records/3441495/files/Opara%20et%20al_2.pdf>
Maybe it's an attempt to promote the sale of Hoppe's No. 9 air
freshener? <https://www.google.com/search?q=hoppe%27s%20no%209%20air%20freshener>
EU version of MSDS Sheet for Hoppe's No. 9 Gun Bore Cleaner: ><https://www.copquest.com/knowledgebase/MSDS_Hoppes_No_9_Solvent.pdf>
Ingredient CAS No % WT
1 Kerosene 008008-20-6 15 - 40
2 Ethyl Alcohol 000064-17-5 15 - 40
3 Oleic Acid 000112-80-1 - -
4 Amyl Acetate 000628-63-7 5 - 10
5 Ammonium Hydroxide 001336-21-6 1 - 5
The pleasant odor is Amyl Acetate: ><https://www.cdc.gov/niosh/npg/npgd0031.html>
"Colorless liquid with a persistent banana-like odor"
The unpleasant odor might be the use of industrial kerosene instead of >de-odorized (low-sulfur) kerosene, which is used for kerosene lamp
oil, kerosene heaters, diesel fuel etc. My guess(tm) is the factory
used the wrong type of kerosene: ><https://wintersunchem.com/product/low-odor-based-solvent-deodorized-kerosene/>
On 5/17/2026 9:12 PM, Jeff Liebermann wrote:
On Sun, 17 May 2026 19:40:37 -0500, AMuzi <am@yellowjersey.org> wrote:
Last year there was a brief discussion here about the
wonderful smell of Hoppe's No.9 firearm cleaner.
Last week I bought a fresh bottle and. after perforating
targets last evening I opened the new bottle this morning.
It's changed! Smells horrible, like a teen boy who just
discovered body spray. Yecchhh.
A quick search shows that others have noticed as well, at
least one of whom is a chemist. In an all to typical story,
the distinctive odor was from nitrobenzine, which is now
disfavored by the EPA.
I found some vintage No.9.
EU version of MSDS Sheet for Hoppe's No. 9 Gun Bore Cleaner:
<https://www.copquest.com/knowledgebase/MSDS_Hoppes_No_9_Solvent.pdf>
Ingredient CAS No % WT
1 Kerosene 008008-20-6 15 - 40
2 Ethyl Alcohol 000064-17-5 15 - 40
3 Oleic Acid 000112-80-1 - -
4 Amyl Acetate 000628-63-7 5 - 10
5 Ammonium Hydroxide 001336-21-6 1 - 5
The pleasant odor is Amyl Acetate:
<https://www.cdc.gov/niosh/npg/npgd0031.html>
"Colorless liquid with a persistent banana-like odor"
The unpleasant odor might be the use of industrial kerosene instead of
de-odorized (low-sulfur) kerosene, which is used for kerosene lamp
oil, kerosene heaters, diesel fuel etc. My guess(tm) is the factory
used the wrong type of kerosene:
<https://wintersunchem.com/product/low-odor-based-solvent-deodorized-kerosene/>
You can remove some of the smell with activated charcoal filtering,
but I don't know what it might do to its gun bore cleaning abilities.
<https://zenodo.org/records/3441495/files/Opara%20et%20al_2.pdf>
Maybe it's an attempt to promote the sale of Hoppe's No. 9 air
freshener?
<https://www.google.com/search?q=hoppe%27s%20no%209%20air%20freshener>
I will assume any EU approved product will be useless. And
'safe'!
https://www.1911forum.com/threads/hoppes-no-9-the-original-revised.700145/
On Sun, 17 May 2026 19:12:49 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
EU version of MSDS Sheet for Hoppe's No. 9 Gun Bore Cleaner:
<https://www.copquest.com/knowledgebase/MSDS_Hoppes_No_9_Solvent.pdf>
Ingredient CAS No % WT
1 Kerosene 008008-20-6 15 - 40
2 Ethyl Alcohol 000064-17-5 15 - 40
3 Oleic Acid 000112-80-1 - -
4 Amyl Acetate 000628-63-7 5 - 10
5 Ammonium Hydroxide 001336-21-6 1 - 5
The pleasant odor is Amyl Acetate:
<https://www.cdc.gov/niosh/npg/npgd0031.html>
"Colorless liquid with a persistent banana-like odor"
The unpleasant odor might be the use of industrial kerosene instead of
de-odorized (low-sulfur) kerosene, which is used for kerosene lamp
oil, kerosene heaters, diesel fuel etc. My guess(tm) is the factory
used the wrong type of kerosene:
<https://wintersunchem.com/product/low-odor-based-solvent-deodorized-kerosene/>
Some more detail. The original odor was from a mixture of kerosene
and banana oil (isoamyl acetate). <https://en.wikipedia.org/wiki/Isoamyl_acetate>
I couldn't find anything on which type of kerosene and its sulfur
content was used.
Oleic acid was likely chosen as a de-oxidising agent, probably because
it is considered food safe. It's the active ingredient in some
electrical contact cleaners. Please do NOT test this by consuming
some Hoppe's No. 9 cleaner.
On Sun, 17 May 2026 21:29:53 -0500, AMuzi <am@yellowjersey.org> wrote:
On 5/17/2026 9:12 PM, Jeff Liebermann wrote:
On Sun, 17 May 2026 19:40:37 -0500, AMuzi <am@yellowjersey.org> wrote:
Last year there was a brief discussion here about the
wonderful smell of Hoppe's No.9 firearm cleaner.
Last week I bought a fresh bottle and. after perforating
targets last evening I opened the new bottle this morning.
It's changed! Smells horrible, like a teen boy who just
discovered body spray. Yecchhh.
A quick search shows that others have noticed as well, at
least one of whom is a chemist. In an all to typical story,
the distinctive odor was from nitrobenzine, which is now
disfavored by the EPA.
I found some vintage No.9.
EU version of MSDS Sheet for Hoppe's No. 9 Gun Bore Cleaner:
<https://www.copquest.com/knowledgebase/MSDS_Hoppes_No_9_Solvent.pdf>
Ingredient CAS No % WT
1 Kerosene 008008-20-6 15 - 40
2 Ethyl Alcohol 000064-17-5 15 - 40
3 Oleic Acid 000112-80-1 - -
4 Amyl Acetate 000628-63-7 5 - 10
5 Ammonium Hydroxide 001336-21-6 1 - 5
The pleasant odor is Amyl Acetate:
<https://www.cdc.gov/niosh/npg/npgd0031.html>
"Colorless liquid with a persistent banana-like odor"
The unpleasant odor might be the use of industrial kerosene instead of
de-odorized (low-sulfur) kerosene, which is used for kerosene lamp
oil, kerosene heaters, diesel fuel etc. My guess(tm) is the factory
used the wrong type of kerosene:
<https://wintersunchem.com/product/low-odor-based-solvent-deodorized-kerosene/>
You can remove some of the smell with activated charcoal filtering,
but I don't know what it might do to its gun bore cleaning abilities.
<https://zenodo.org/records/3441495/files/Opara%20et%20al_2.pdf>
Maybe it's an attempt to promote the sale of Hoppe's No. 9 air
freshener?
<https://www.google.com/search?q=hoppe%27s%20no%209%20air%20freshener>
I will assume any EU approved product will be useless. And
'safe'!
I mention the "EU version" because the ingredients list I provided and trimmed included the European chemical classifications. I didn't
bother trying to find the European version of the MSDS sheet because I
also assumed they had approved Hoppe's No. 9.
I wouldn't know if European products are useless. I get most of my consumables from China. Some is formulated in the US. I don't have
anything in my chemical locker from the EU.
https://www.1911forum.com/threads/hoppes-no-9-the-original-revised.700145/
Good article and thanks. I didn't know about the difference between
isoamyl acetate and amyl acetate. I also didn't consider the
possibility of a mixture to fine tune the odor:
"Hoppe's #9 may be a mixture of the two acetates, and their
proportions are likely proprietary. Careful manipulation of there
proportions would likely yield something very close in all respects."
Incidentally, the author mentions a change in formulation that might
reduce the ability to clean copper. I think that might be why the
chart does not include a % WT figure for oleic acid. Oleic acid
attacks copper. Contact cleaners, such as the original Deoxit
formulation, include a warning to remove any residue from the contacts
with a solvent, after applying Deoxit to prevent damage to copper
contacts. <https://www.eevblog.com/forum/metrology/contact-cleaner-for-metrology-grade-connections/>
On 5/17/2026 9:51 PM, Jeff Liebermann wrote:
On Sun, 17 May 2026 19:12:49 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
EU version of MSDS Sheet for Hoppe's No. 9 Gun Bore Cleaner:
<https://www.copquest.com/knowledgebase/MSDS_Hoppes_No_9_Solvent.pdf>
Ingredient CAS No % WT
1 Kerosene 008008-20-6 15 - 40
2 Ethyl Alcohol 000064-17-5 15 - 40
3 Oleic Acid 000112-80-1 - -
4 Amyl Acetate 000628-63-7 5 - 10
5 Ammonium Hydroxide 001336-21-6 1 - 5
The pleasant odor is Amyl Acetate:
<https://www.cdc.gov/niosh/npg/npgd0031.html>
"Colorless liquid with a persistent banana-like odor"
The unpleasant odor might be the use of industrial kerosene instead of
de-odorized (low-sulfur) kerosene, which is used for kerosene lamp
oil, kerosene heaters, diesel fuel etc. My guess(tm) is the factory
used the wrong type of kerosene:
<https://wintersunchem.com/product/low-odor-based-solvent-deodorized-kerosene/>
Some more detail. The original odor was from a mixture of kerosene
and banana oil (isoamyl acetate).
<https://en.wikipedia.org/wiki/Isoamyl_acetate>
I couldn't find anything on which type of kerosene and its sulfur
content was used.
Oleic acid was likely chosen as a de-oxidising agent, probably because
it is considered food safe. It's the active ingredient in some
electrical contact cleaners. Please do NOT test this by consuming
some Hoppe's No. 9 cleaner.
A comment in a firearms forum by a chemist mentioned that
nitrobenzene has an almond smell which, with the banana
ester, made the distinctive odor.
On Mon, 18 May 2026 07:32:23 -0500, AMuzi <am@yellowjersey.org> wrote:
On 5/17/2026 9:51 PM, Jeff Liebermann wrote:
On Sun, 17 May 2026 19:12:49 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
EU version of MSDS Sheet for Hoppe's No. 9 Gun Bore Cleaner:
<https://www.copquest.com/knowledgebase/MSDS_Hoppes_No_9_Solvent.pdf>
Ingredient CAS No % WT
1 Kerosene 008008-20-6 15 - 40
2 Ethyl Alcohol 000064-17-5 15 - 40
3 Oleic Acid 000112-80-1 - -
4 Amyl Acetate 000628-63-7 5 - 10
5 Ammonium Hydroxide 001336-21-6 1 - 5
The pleasant odor is Amyl Acetate:
<https://www.cdc.gov/niosh/npg/npgd0031.html>
"Colorless liquid with a persistent banana-like odor"
The unpleasant odor might be the use of industrial kerosene instead of >>>> de-odorized (low-sulfur) kerosene, which is used for kerosene lamp
oil, kerosene heaters, diesel fuel etc. My guess(tm) is the factory
used the wrong type of kerosene:
<https://wintersunchem.com/product/low-odor-based-solvent-deodorized-kerosene/>
Some more detail. The original odor was from a mixture of kerosene
and banana oil (isoamyl acetate).
<https://en.wikipedia.org/wiki/Isoamyl_acetate>
I couldn't find anything on which type of kerosene and its sulfur
content was used.
Oleic acid was likely chosen as a de-oxidising agent, probably because
it is considered food safe. It's the active ingredient in some
electrical contact cleaners. Please do NOT test this by consuming
some Hoppe's No. 9 cleaner.
A comment in a firearms forum by a chemist mentioned that
nitrobenzene has an almond smell which, with the banana
ester, made the distinctive odor.
Yep. Apparently, the formulation changed. I couldn't find a date for
the change.
<https://www.shootersforum.com/threads/did-hoppe-change-no-9s-formula.242744/?post_id=2317054&nested_view=1#post-2317054>
"Hatcher said an analysis done about the time of WWII showed it was:
Ammonium oleate 16%
Neutral saponifiable oil 24%
Nitrobenzene 6%
kerosene and amyl acetate 54%
The neutral saponifiable oil is probably banana oil.
Nitrobenzene is toxic and a carcinogen, to boot, so it has
been removed since then."
Nitrobenzene is some nasty stuff. Please be careful with your old
bottle of Hoppe's No.9:
<https://en.wikipedia.org/wiki/Nitrobenzene#Safety>
"It is classified as an extremely hazardous substance in the United States..."
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