You must be doing it wrong.
What's the "black residue" in the grooves? That might be better answewred by first answering "What are you using (product type/name) to clean with?" You also need to tell what you are shooting - FMJ, bare lead, some exotic supermetal?
It will also help if you mention what you are using to spread the product type/name about in the barrel & cylinders.
BTW - there is some (not much, but some) truth to the old saw that you can
overclean some things, and can accelerate wear by brushing too much.
By black resedue i meant carbon resedue which comes out on the patch. Even after multiple patch runs it still comes out with some black stripes on it where it touched rifling grooves. I use Hoppes # 9 on the snake (for hanguns) and then on patches which i put on a brass jag - pretty standard. That was for the barrel. As for the rest of the gun, i use same Hoppes #9 ona nylon toothbrush first, then on a simple cloth. This part doesn't take too long - its barrel which just seems uncleanable... I normally shoot simple FMJ target ammo - Federal, Independence or Winchester. Any ideas what i'm doing wrong?
OK then! I think we have found the problem.
Sounds as of you are not
using a bore brush - just a bore snake of some variety. Use of a bore brush (preferably from chamber to muzzle one way only) a few times could help. If you must go from muzzle to chamber it is OK, although you may want to put a rag over the back end to prevent drips from getting down into the action.
Another "trick" is to squirt carb cleaner/brake cleaner (either one, not both at once) down the bore - chamber to muzzle only) to flush out carbon before you do anything else.
And since you are shooting FMJ you might want to occassionally add a copper remover. I favor the foams and let it stand for at least 15 minutes before running patches through. (No bronze brushes, although stainless or plastic are OK and their use is recommended- copper solvent will eat phosphor brushes.) Once you use a copper remover, do not use phosphor or brass jags until you clean it out of the bore - otherwise you will be dissolving your jags bit by bit.
If you use copper remover, check your patches for blue color - if present it means you still have copper somewhere. Once you get to gray you are good to go.
You will NEVER get a perfectly clean patch out of your bore unless you have scoured the bore completely clean of all copper. brass, lead and carbon. Your bore should look smooth - no lands or grooves - to be that clean.
If you are really paranoid, find someone with a borescope and have a look-see as to what's in there and what condition the bore is in. Once you have looked ypu will be even more paranoid.