Have a standard Phosphate AR chrome lined barrel. If I wanted to give it the best black corrosion resistant coating what would that be? I have been looking to ionbond the barrel GB and flash hider. Any other suggestions?

What I'd do is completely degrease the barrel then give it a coat of moly resin over the parkerizing.

I have looked at that also. Also cerakote. Anyone have any advice between ionbond, cerakote, and moly resin?

Lets try this again, I have started to look into this and I have been drawn to melonite and ionbond. What I am looking for is the best corrosive protection. As close to a no worry coating for the barrel, gb, and flash hider. Any opinions?

Melonite (nitride) processes are out of the question since you have a chrome lined barrel.

What I'd suggest if you're really that intent on something with maximum corrosion protection is to start over with a QPQ nitrided CMV barrel, and then coat the exterior with ionbond for additional protection.

I don't think so.
Melonite is a little different than IonBond.  IonBond can be applied to a barrel without being applied to the bore & chamber.

This seems like overkill to me.  Where are you goin?, a valley with a lake of sulfuric acid?

Seriously, people have used barrels with a lot less corrosion resistance than what is commonly, cheaply available today, in environments I don't even want to think about.  Plus, they had to deal with corrosive ammunition.

Maybe I don't understand what you are trying to achieve.  The best finish is not going to replace proper maintenance.

Of course regular maintenance is the best way. And I am sure that with it the phosphate is just fine. But if I have some extra money and want to improve the rifles resistance to corrosion, what's wrong with that?

To answer your question I am simply trying to make what I have as corrosion resistant as possible with today's tech. Obviously some of this tech wasn't around years ago. Older tech still works just fine but something tells me your not still running a dos computer

I appreciate the interest in advancing the art but you're really going to run in to diminishing returns here.  As an example, QPQ nitride is a good corrosion resistant finish.  Put something on top of it, and it's improved... but even a wide variation in the amount of improvement would not make much difference in the overall performance of the combination.

I can understand that but are you saying there is no coating that you could put on a phosphate barrel that would, a) realistically improve corrosion resistance, or b) is not cost efficient for the price.  

You mention qpq nitride. Can this be applied to a chrome lined barrel and who does this?

You have several contradictions in your line of thinking.  Are you looking for a coating to put on a phosphated (parkerized), chrome lined barrel, or are you looking at other alternatives?  Most of the things you discuss are not compatible to just apply to the barrel you have.

As an example, as I already mentioned nitride is impossible with a chrome lined barrel.   Nitride is a process in which the entire bare steel part is immersed in various liquid baths at high temperatures (~1000 degrees F) to achieve the chemical transformation of the surface.  Metallic chrome plating would not only be destroyed but would ruin the chemical bath of the nitriding company in the process.  Similarly a parkerized surface is not compatible with nitride and would have to be removed.

Ion bond is similar, it would need to be applied to a compatible surface, which parkerizing (AFAIK) is not.

So you really need to clarify your question.  Do you want to add something to the barrel you have, or are you starting over with a new barrel for your ultimate corrosion resistant finish?  My first response in the thread was my most reasonable suggestion for something effective to coat your existing barrel with (moly resin), in combination with the porous nature of the parkerizing this would create a very durable and corrosion resistant finish.

Sorry I do see you said nitride or melonite are not comparable. Sorry, I keep thinking these are different processes. Honestly I prob keep getting confused with several different names for the same thing.

And I thought ion bond was compatible so I will have to go back and look again.

As far as moly resin, is this similar to the duracoat or cerekote types of finishes? I have read and seen some testing for cerekote. How does moly resin compare.

So as far as moly resin, where or who would you suggest? Don't have a spray gun and would just prefer it done right.

I thought you had to have a spray gun?

Airbrush... little craft store ones are not very expensive.

Got a recommendation as to a particular brand/type?