Some of the cheaper new brass rounds have a gold colored coating on them (ZSR).  This gold coating flakes off and leaves a mess in the gun.  It gunked up my Glock enough to cause light strikes after several hundred rounds.  What is it and why do they use it?  

Gold colored bullet

 

 

Copper colored bullet

 

It is probably a poorly done copper wash.  Similar to how 22lr is coated.

The answer is going to be specific to the particular ammo, and require more info on what you are talking about about "flaking". 

Seldom is the jacket of an actually jacketed round pure copper, but rather an alloy.  For some ammo, the jacket is actually brass. Typically a brass alloy identical to the case material. For those that specify, they usually refer to this as gilding metal jackets.  If the manufacturer can manufacture both cases and jackets from the base stock (usually metal ribbon where they punch planchets out of it), it reduces cost due to economies of scale (i.e. they can negotiate better prices when they buy more). These will not flake.  Montana gold bullets are a good example of this. Also sometimes RMR bullets uses gilding metal. 

Then you have plated lead bullets. These will look like copper because they are copper. The chemical plating process requires copper. In general these won't flake, but can under certain circumstances. 

Then you have plated steel jackets. This is a soft mild steel plated with something that resembles gilding metal. S&B has skus like this. I haven't used them and have no idea if they flake. But all the examples I know of are cheaper eastern european ammo, so ZSR would be a candidate for them. They often tend to use steel cases that have been plated to look like brass. 

Which brings us back to the flaking. Do you have pics? Because it is not uncommon for there to be brass dust in the fouling on a gun with any brass cased ammo. It comes from the action of feeding a round and the minor scraping that occurs on the cartridge. But it tends to look like  someone took a file to brass, not flakes, with the naked eye.

I'd take a magnet to the cartridge, both projectile and case, and pick up some of the casings after use to see if the plating is scraped off. 

 

Montana Gold uses a gold color for their bullets as well, although they are a very good quality.

Is it inaccurate?

Here is the round with the gold colored coating/plating.  

 

This is the mess it leaves behind after just under 100 rounds.  

 

 

This is after I tried cleaning it.  Some still there.  Needed to be blasted away with half a can of gun scrubber to get it all.  

 

That looks more like unburned smokeless powder residue to me. 

I agree.  Cheaper is not always better.

10 hours ago, JohnnyB said:

That looks more like unburned smokeless powder residue to me. 

It's the exact same color as the coating on those bullets. It looks like its coated after its pressed together, then when the bullet separates from the case, parts of the coating come off near where the bullet meets the case?  

I know that silver bullets are for werewolves, but not so sure about gold.