giggitygiggity
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- Mar 18, 2009
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I have seen a number of AR barrel finishes offered to include phosphate, melonite, nitride, QPQ, etc. What are the pros and cons to each finish and what do you recommend? Thanks!
Not to nitpick, @badkarmamib, but they don't pour molten chrome down the bore of a chrome-lined barrel. It's done via an electroplating process that only lines the bore of the barrel. (Easy enough to do. Fill the barrel with your plating solution and plug the ends, then hit it with your electrodes to deposit the plating material.) However, plating isn't always very even/uniform. And since they oversize the bore and try to adjust the plating thickness to get back to the desired bore size, @badkarmamib is correct that it's not the most-accurate option available. But, it provides benefits of some wear resistance, corrosion resistance, etc. over a plain or phosphate-coated barrel, which is why it's used in mil-spec barrels.
Phosphate coating is okay. It does provide minimal protection over an uncoated barrel. It's black. But, it's not very wear-resistant. I've worked with phosphate coating at my previous job, and it really didn't do all that much to protect the coated parts. Mostly, we used phosphate as a good intermediate step to allow paint to adhere better. This is because it creates a little extra texture on the metal surface, which also means it will hold onto lubrication better than an uncoated part. I wouldn't choose this coating, unless I really wanted a budget build and it was my only option.
I'm building my first AR, and I decided to go with a nitrided barrel. The combination of better wear and corrosion resistance was very attractive to me. I found a nitrided barrel online on sale, which worked well for my build.
If price is equal across the board, I'd go with nitride coating first.
Not to nitpick, but chrome plating is not done like that either….
Hard chrome electroplating barrels is done is basically done in two steps:
First, you electro etch the barrel, this can be thought of as reverse plating. Instead of depositing material from the electrolyte solution onto the target, material from the target is removed and placed into the electrolyte. Then the bore is plated to resort the removed thickness.
The two processes are basically the same:
With rifle a barrel, the barrel is placed vertically in a solution tank so that the entire barrel is submerged and the breech end is clear of the tank bottom. A movable button electrode is placed in the bore at the chamber end and centered. The barrel itself is the other electrode. Solution is forced down the bore and around the button; this keeps the button centered in the bore to very tight tolerances, as well as keeps a constant supply of fresh solution at the point of action.
The button is pulled from the breech end to the muzzle end with current flowing through the solution and removing, or depositing material, the speed of the button can be varied to account for the different clearance between the button and the bore (say at the chamber), and it allows for the removal/deposition of thicker layers as required. In this manner, the bore itself can be plated to a thicker level than the chamber.
The current, the clearance and the duration the electrode is in proximity to the bore establishes the concentricity and thickness of the plating. A good, well established, barrel plater can maintain 2 to 5 millionths of a millimeter (microns) in diametrical thickness variation and 2 to 5 microns in thickness variation over the length of an average (20 inch) barrel.
The Idea that chrome plating leads to gross bore variations is mostly a myth created by people selling nitride. While nitride does not alter the surface, so what you start with is what to end up with, chrome plating can be damn accurate.
Also, as with any barrel, if you start with a crappy bore, neither chrome plating, nor nitride will make it a good barrel.