Two new uppers I have, a Bushy M4 and a Dpms M4 are new and only factory test fired. Both are chrome lined. I swabbed them out with break-free when I got them and stuck them in my safe for a few months not thinking anything of it. Now I notice especially with the Dpms that the chamber face nooks and crannys just won`t come clean even after moderate chamber brush use. Whatcha think and recommend??

My first guess would be a carbon build up, which is normal.

Unless it’s heavy, I wouldn’t worry too much about it.  Scrubbing the chamber with a chamber brush and a bore solvent (Shooter’s Choice, Hoppes No. 9, or whatever) should loosen it up.  You may have to scrub a bit since carbon can be hard to loosen up.

Then patch the chamber out with about a .30 cal patch and see what you get.  If it was carbon, you should get a black residue.

If the chamber throat is part of the problem, you may also need to clean with a new .22 cal bore brush and solvent, followed by .22 patches

Note that you don’t try to push the .30 patch into the smaller, rifled part of the bore or it might get stuck.  Also note that if you use a copper cutting type bore solvent, be sure and clean your chamber brush and/or bore brush afterwards, or the solvent will attack the bronze bristles.

When you’re finished and have patched all the solvent out, give the chamber and locking lugs areas a light coat of CLP or such.

If you’ve been using Wolf ammunition, what you’re seeing might be some sort of lacquer build up.  Cleaning the chamber as described above should also handle this.

I can’t imagine that you’ve got rust in a chrome-plated chamber.  If you do, the patches should come out with a dark reddish-brown residue, though any carbon mixed in might make it look black.  

Well, the deposits are a brownish color and are not in the chamber but in the area in between the locking lugs on the bolt extension and the chamber. I soaked everything overnight with breakfree and got most of it out but you would think that damn chamber brush would take care of it. Is there a good bore cleaner that would do a better job??  Like I said these are new uppers right out of the box, only test fired at the factory. I thought I had them thoroughly cleaned and lubed before I put them away.

I think it's still not polished out from firing aka 'broken in'.  Mine Bushy was that way until I had about 500 rounds through it.  I believe Bushmaster says not to clean for the first 200 anyway.  I only ran a bore snake down mine after 200 rounds and only wiped out the chamber with CLP.  I didn't use a chamber brush until 1000 rounds.  And a bore brush until 500 rounds.  Most of the time I don't use a bore brush, usually just a chamber brush followed by the bore snake.

I just took my chamber brush, chucked it a variable speed drill and got most of it. My bad, it was the barrel extension that had the gunk build-up and probably was a little surface rust. I will check more often than every few months now in between lubing.