Hoppes #9 if left for a while comes out green if there's copper, so it DOES remove it.
Here's one from my prepper files, I obtained from Frugal Squirrel, homepage for patriots back in the late '90s
Quote:
Combat Arms
2869 Grove Way
Castro Valley, California 94546-6709
Telephone (415) 538-6544
BBS = (415) 537-1777
REMOVING COPPER FOULING FROM RIFLE BARRELS
As a copper jacketed bullet passes through a rifle barrel, it leaves a
tiny trace of copper on the lands and grooves of the rifling within the
barrel. The more the weapon is fired, the greater the amount of copper
deposited within the barrel. The copper begins to fill the grooves and the
accuracy of the rifle will drop off considerably. What you will initially
notice is that the shot groups will begin to widen as well as start to
stray from point of aim.
The obvious cure for this problem is to simply remove the copper from
the barrel! That's where the fun begins. The shooter typically uses
Break-Free CLP, Hoppe's No. 9, Shooter's Choice or some less well known
substance. Anyone who has ever seriously cleaned a barrel will know the
labor involved in doing it correctly. The use of the bore brush rubbing
against the inside of the barrel increases the likelihood that, sooner or
later, the rod will ding the barrel and that will do nothing for accuracy.
Worse yet, if you clean the barrel from the muzzle end and ding the barrel
area within one inch of the muzzle, you can cause damage which will upset
the correct bullet flight path (trajectory).
Chemically removing the copper
If we could safely chemically remove the copper, we would lessen
the real chance of barrel damage. The problem then arises for a way to do
the chemical removal without damaging the weapon. One of the best ways to
remove copper from anything is to coat the copper with a solution contain-
ing ammonia. In more concentrated forms it is called ammonium hydroxide.
When copper comes into contact with ammonia, it begins to dissolve. To
see an example of this phenomena, drop a simple one cent coin into a cup of
household ammonia. It will take a bit of time to do it because the house-
hold ammonia is a 9% solution and the variety sold by Combat Arms is a 28%
solution. Our type is sometimes known as "aqua of ammonia."
Preparing the copper removing cocktail
To chemically remove the copper fouling, get an uncontaminated bottle
of Hoppe's No. 9 and pour half of the bottle of Hoppe's No. 9 into another
small sealable container. Now take our 28% solution of ammonium hydroxide
(this is also called ammonium hydroxide rated at 26ø on the Baume' scale)
and top off the bottle of Hoppe's No. 9 with this ammonium hydroxide. This
gives you a copper removing cocktail made up of Hoppe's No. 9 and aqua
ammonia in a 50-50 solution. The only thing even remotely critical here is
to follow these steps.
SAFETY INSTRUCTIONS
1. Always mix up your copper removing cocktail using a fresh and un-
spoiled bottle of Hoppe's No. 9. It is easier to use this cleaning
method when you use the wide mouth 4 ounce size of Hoppe's No. 9. So,
spend some money on a new bottle of Hoppe's No. 9.
2. The fumes of this concentrated ammonium hydroxide can be a bit
overpowering, so do not mix this solution in a closed room. MIX THIS
SOLUTION UP OUTSIDE WHERE THERE IS PLENTY OF VENTILATION! Concentrated
ammonium hydroxide will really clean out your sinuses.
3. If you spill any of the ammonium hydroxide on your skin, you should
wash it off immediately in clear, cold running water to avoid any
possible sensitivity and irritation.
Applying the solution
To clean the barrel now becomes a simple job. Just position the weapon
muzzle down in a plastic bucket that has some rags in the bottom of the
bucket. The purpose of having the rags underneath the muzzle is to catch or
collect all of the contaminants and fluid coming out of the barrel. The
reason behind the bucket is to prevent the rags from contaminating the
flooring the bucket is on. For Pete's sake, don't be so stupid as to try
this over your wife's new carpet because you will be moon bound if you do!
Now take an eyedropper and carefully fill it with the cocktail. Then
drop the cocktail into the chamber end of the barrel with the eyedropper.
Rotate the barrel to get the cocktail over all of the internal surfaces of
the barrel.
Once the inside of the barrel is sufficiently covered with the
cocktail, it is necessary to give the solution some time to dissolve the
copper. So, go eat breakfast/lunch/dinner, mow the grass or something for
15-20 minutes while the chemistry does its magic. While you are doing
something else, your barrel is really cleaning itself!
The finishing touches
Once the ammonium hydroxide has had a chance to work on the copper,
you then need to swab out the barrel and put a coat of Break-Free CLP or
other gun oil on the inside and outside of the barrel. The barrel is now
copper free!
Because of the mess this makes (the rags that were under the muzzle
will have a blue-green tint to them indicating the copper is coming out of
the barrel), Combat Arms recommends that you clean all of the other parts
of the gun before you treat the barrel.
If you will treat the barrel with this method after about 250 to 500
rounds, you will be much more satisfied with your weapon's accuracy.
Something that some of our shooters do is to carry a bottle containing the
cocktail with them to the range. Then, during a lull in the shooting, they
simply put a patch on a cleaning rod, dip it into the cocktail and run the
patch down the barrel. This is then followed by a series of dry patches
until the bore is completely dry. The gun is now ready to fire again. This
procedure is used to keep the copper from building up and reduces the need
to strip all of the copper out as previously outlined.
