I have been using Hoppe's Nr 9 bore cleaner for about 60 years. One thing I liked about it is that it was safe to use, you could leave it in the bore for extended periods of time. The Directions recommended running a wet patch through the bore after it was clean. 
Today I emptied by bottle of Hoppe's Nr 9 and opened a new bottle. I noticed that the label says "Traditional" on it and it also says "Corrosive". 
the directions now state you should clean the bore, run a dry patch through (presumably to remove the solvent) then apply oil to the bore. 
Apparently it is no longer safe to leave the bore wet with Hoppe's Nr.9, which is too bad, I am not interested in using a product if I have to remove it in order to prevent damage. 
I suppose the word "corrosive" could be limited to brass and copper, but then why would they recommend removing the product and applying oil?
Before I get a flood of e-mails saying "I have been using Hoppe's #9 for years without problems, make sure your bottle says "corrosive".
Not sure what to do with the bottle that I have, maybe I can use it to start my charcoal grill. I like the aroma of Hoppe's, not sure about the taste. 
Joe S

Went shopping this afternoon to see if there was a version of Hoppe's Nr9 that did not say "corrosive", tried two stores, no luck. Lots of other products to choose from, but I am a little leery of mixing different products. I have some  old Outers Gunslick bore cleaner that recommends you run a wet patch through after cleaning to "annoint" the bore, never had a problem with it. Apparently its no longer available. I also have some Ballistol, which is probably what I will use unless something better comes along. According to the label, its good for just  about anything that ails you, never heard anything bad about it, except it has a strange smell. 
I did contact Hoppes, no answer yet. Will let you know what I find out. 

Joe S

Someone asked Hoppes and got this reply.

Thank you for contacting Bushnell customer support. I’ll be happy to help you.

The Hoppes 9 is the original formula with ammonia that is highly corrossive. You want to make sure not to let it sit on non metallic parts as it can cause damage to those parts. The Synthetic Blend is a non toxic, ammonia free cleaner that is much less corrossive and not as likely to damage non metallic materials. For complete information regarding the chemicals in the solvents and proper use, refer to (You need to Login or Register to view media files and links) for the material safety data sheet info on them.

Another post on 24 hour cmpfire says no:

It is true that "ammonia" can damage steel. Several copper-removing bore cleaners contain ammonium hydroxide, just as does Hoppe's #9. (Sweet's is a good example.) These bore cleaners warn not to leave the cleaner in a bore more than about 15-20 minutes, before patching it out. The reason is that oxygen from the atmosphere will dissolve into the liquid of the bore cleaner. The oxygen reacts with the ammonia, producing products that can etch steel.

This does not happen with Hoppe's #9. As the MSDS sheet indicates, Hoppe's #9 is also formulated with oleic acid. This acid reacts with ammonium hydroxide, a base, to produce ammonium oleate and water. Ammonium oleate does not react with steel, but will dissolve copper.

So, there are no worries with leaving Hoppe's No. 9 in the bore for long periods.

So the answer is yes and no

I use Kroil

Jack

This will be heresy, I know, but I detest the smell of Hoppes #9

And along the same vein, there are several oils that I truly enjoy the aroma of, Kroil, MML, and plain old sewing machine oil, 3 in 1

Go figure, right?

Good Old #9

Kurt_701 wrote on Sep 20^th, 2021 at 11:21pm:



We should be getting a check from Hoppes........

Hello everyone, 
Here is the official answer from Hoppe's:

"Joe,
Thank you for contacting Bushnell Customer Support.   I’d be happy to help you with this question.   

That is correct, you do not want to leave solvent in the bore. Run some dry patches thru and then apply oil

If we can be of further assistance, please contact us again via email at CustomerSupport@Bushnell.com.
We appreciate your business.  Thank you. "

I think they should change the label to remove the word "Traditional" because it falsely implies that this is the old product that could be safely left in the bore. Not holding my breath on that. 

For the time being, I will be using Ballistol. Anyone aware of any problems with that product?
Thanks!
Joe S

of course!