In my Ak-USA build I noticed after bump-firing a lot of 5.45x39 Wolf the inside of the receiver area was caked in red debris of some kind.  What is it?

I believe its the sealent, the red stuff around the primer if you look at the bullet. I usually have it all over my trigger mech and at the bottom there. Its used to seal the ammunition against moisture.

Its an AK, You can throw a handful of gravel in there with the "red primer specs" and the gun will function no different.
Every few years, you may want to blow that shit out of there with an aerosol or solvent rinse of some sort just for "looks."
...but it really doesn't matter.

RS39,
I feel you are wrongfully accusing me.

I was simply trying to graphically illustrate the point to the kid that his AK isn't like other guns, and it will function flawlessly without a thorough cleaning.  How could you accuse me of "talking trash?"  I was just answering his questions.  It was not an argumentative response.

Admittedly, there was a reason before when you sent Templar to straighten things out with me.  I did take Templar's recommendation seriously, and when he told me to "tone things down"  I have done just that.  Any argumentative tone in my writing was meant to be sort of funny, like R. Lee Ermey at his show "Mail Call" on the History Channel.  But guys like you had to blow things out of proportion and CREATE a controversy.  Not once did I personally attack anyone at the board or resort to name calling and the like.  But that is how you've apparently made things out to be.  I have discussed this matter with Templar, whom I might add is a reasonable, honest, fair and just man.  But I feel that you are wrongfully attacking me at this point and abusing your authority as a staff member here at the board.

Furthermore, if you look at other posts from me here in the Maintenance and Cleaning forum you will see that I have been offering my opinion and practical advice for those less knowledgeable members here at the board.  I am not "talking trash" as you have mentioned.

Sincerely, maschinengewehr

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An AK is known generally for it's ability to function under the most adverse conditions, however there is no excuse for not applying due dilligence with regards to it's maintenance.

Personal attacks,underlying issues aside,

Mauser, yes as other members have mentioned those red specks are remnants of the lacquer sealant used on the primers.  I receive them also and notice them after an extended range session.  One good cost effective way to flush the sludge/firing residue from your receiver is to purchase an aerosol can from harbor freight. (about 10 bucks) then fill the aerosol can 3/4 of the way with ED's Red solvent (you can make it your self for under 20 bucks per gallon)  If you want the simple formula IM me.  ED's will remove the stubborn powder residue but be advised it contains acetone and will attack some painted finishes.

Rock on guys.