I recently bought a M&P 15 Magpul model, the one with the mid length gas tube, 5R rifling, and nitrided barrel (I forget the S&W trade name for it).
I have noticed that the barrel seems to accumulate more copper fouling than my other rifles, possibly due to the higher bullet velocity. I normally would use Sweet's copper fouling remover to deal with this, but I read in the owner's manual that S&W have cautioned against using cleaners containing ammonia on this gun. I assume this is because of the nitrided surface.
Anyhow, I am using Hoppe's #9 and the patches continue to turn blue much longer than they would in my other rifles.
I am wondering why so much copper, and if you guys have the same issue. What are you using to remove the copper?
Also, I have seen references to cleaning the gas tube, although my owner's manual does not mention this procedure. Should I be cleaning the gas tube? If so, how and with what? Looks like I would have to remove the front gas block/sight assembly to do this. Kind of a pain.
Thanks in advance for your replies.

Can't answer your gas tube cleaning question as that's one I have myself.

With regard to the copper fouling - I've had great success with Bore Tech products. Normally their Eliminator gets it all but for stubborn copper their Copper Eliminator does the trick for me every time.

Good luck.

Bill

Nothing goes in the gas tube. Putting anything down it leave the possibility of it breaking off in the tube and causing far more problems.

In short leave it be.

For copper, hoppes #9 is a great all around cleaner with the exception of copper there are much better copper solvents. Sweets 762 is pretty strong and I've had good luck with wipe out patch out which also wont kill you with fumes. Ammonia is what eats/dissolves the copper, just don't leave it sitting in a barrel. 10 minutes should be plenty of time, then chase with a dry patch followed by oil and another dry patch to get excess oil out. When you leave ammonia products sitting in your barrel you run into problems, this goes for all barrels.

Might help to keep the rifle right side up while using solvents, prevents fluids from entering the gas ways.

Brownells and Midway have long pipe cleaners that will clean the gas tube. (In the Army we used to clean the M16 uppers in a 50 gal drum of some kind of boiling cleaning solution, smelled like diesel but not sure of what it was. I think we used the same drum to heat the ration cans as well)

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Minimize the variables

I like Shooters Choice. Seems to get the copper out pretty fast but I don`t believe it has ammonia in it.

I use Wipe-Out Patch-Out and Wipe-Out Bore Cleaning Solvent Accelerator. They do not contain ammonia and will not affect the Melonite treatment.

Patch in on, Leave overnight, and you will not believe the amount of color that drips out when you push a clean patch through it in the morning. I've given up scouring bores like a farmer churning butter.

Ask you local gunsmith how gas tubes he has replaced because he couldn't get the pipe cleaner out. If you are truly anal about such thing, squirt some brake cleaner down the tube after cleaning. Just remember to oil the bore.