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Disturbed
03-03-2013, 6:09 PM
I have owned my Colt M4 6920 since October, and have shot about 400-500 rounds (all brass cased)... religiously cleaning the rifle after each use (using Break Free CLP and the methods I learned at USMC OCS).

About a month or two ago I noticed some interesting discoloration on my bolt carrier group, and can't figure out what's causing it. I've tried the CLP mentioned above, and recently Frog Lube, and both have done nothing to fix the stains.

The stains are on the side of the BCG that is visible with the ejection port cover open. The other side of the BCG is immaculate, and there are no discolorations on the inside of the rife that I can see.

Any ideas what is causing this? Or, what I am doing wrong?

Thanks!

b18bturboek9
03-03-2013, 6:14 PM
Looks like dried up CLP or Froglube. As long as it functions and doesnt ruin the BCG keep shooting and enjoy unless u want it to look perfect and pristine then I'd say get a solvent and brush and get to cleaning. Most solvents will make it look dry and chalky afterwards but just hit it up with some clp or whatever oil and it should look fine.

sleepur606
03-03-2013, 6:54 PM
Looks like burnt on lube or oil.

If it worries you enough, try a stiff brush, either brass or stainless but be careful with stainless, or 0000 steel wool to take it off. You just don't want to ruin the finish on the bolt carrier.

Colt562
03-03-2013, 7:40 PM
I would use some 0000 steel wool, lightly try to get it off. Dont want to ruin your finish on the BCG

Dhena81
03-03-2013, 7:50 PM
Don't worry about it.


Even if it was on a friction point which its not it wouldn't matter. It an absolute non issue. I have no idea what could have caused it by you either unless your using some type of other high strength cleaner like paint remover.


I think it was there when you bought the rifle you just didn't notice it until now because what it really looks like to me is a bad phosphate finishing job from Colt. I have a similar stain on the first AK I built and it was from some kind contaminant left on the receiver before I parkerized it.

tomd1584
03-03-2013, 8:06 PM
I would use some 0000 steel wool, lightly try to get it off. Dont want to ruin your finish on the BCG

why even bother? you'll do more damage than good. Leave it be and just shoot the piss out out it.

JDay
03-03-2013, 8:12 PM
Try some Hoppes #9 solvent and a stiff nylon brush, should take it right off.

savagemann
03-03-2013, 9:09 PM
Oh, it's garbage now. You can send it to me for proper disposal. :D

MrPlink
03-03-2013, 9:16 PM
It's probably going to cause all sorts of failures. Lots of jamming due to double feeds, probably even fire out of battery. Very dangerous. Make sure that strange nub on the outside of the ejection port does not have any strange gold coloring on it. Lastly, make sure youre rifle does not make a strange "sproing" side when you fire it, if it does....
Better dump it :p

jeffrice6
03-03-2013, 9:27 PM
Over thinking :)

Disturbed
03-03-2013, 10:20 PM
Thanks for the input guys - I'm not concerned at all about the functionality, I haven't had a single malfunction since I bought the rifle. I just see many more experienced AR owners with spotless BCG's and want to stay on top of my own.

glock7
03-04-2013, 5:02 AM
why even bother? you'll do more damage than good. Leave it be and just shoot the piss out out it.

^this. it's cosmetic, lube it and shoot it. if it does not affect performance, let it be....

glock7
03-04-2013, 5:05 AM
i usually wait 400-500 rounds before i clean it. i used to clean it religiously post shooting, these days not so much. it still functions fine. ymmv

Colt562
03-04-2013, 6:58 AM
why even bother? you'll do more damage than good. Leave it be and just shoot the piss out out it.

I thought the OP wanted a why to clean it. Guess I should go back to reading school :p

saki302
03-04-2013, 5:16 PM
Gas blows out of the holes where the port cover is open- discoloration is normal.

-Dave

vintagearms
03-04-2013, 5:19 PM
I just see many more experienced AR owners with spotless BCG's and want to stay on top of my own.

Thats because they never see the light of day, except in and out of the gun cabinet. They certainly don't see any range time. Marks are normal.

peppermintman
03-04-2013, 5:29 PM
Try some Hoppes #9 solvent and a stiff nylon brush, should take it right off.

That's the way the Army taught me to clean my weapon, solvent then oil. Nothing else. :facepalm:

6mmintl
03-04-2013, 7:40 PM
I would not be seen on the 50/100 yard sniper line with a discolored bolt carrier.