AR Finishes

[giggitygiggity]

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!

 

[badkarmamib]

Phosphate is just a finish on the outside of the barrel, designed to trap oil, thus preventing corrosion. Again, OUTSIDE of the barrel. Inside of the barrel is the same as any hunting rifle, i.e. not well designed for AR applications.

Chrome lined is mil-spec. The bore is oversized, then molten chrome is poured down the barrel. then the bore is electroplated. Great corrosion resistance, easy cleaning, but prone to cracking under high heat (see: full-auto), and uneven plating robs accuracy.

Stainless steel is accurate, and resistant to corrpsion, but will wear out quicker than chrome, since stainless steel is softer.

QPQ, nitrided, melonited, salt-bath, nitrocarbuerized is all the same, which is a surface hardening. IMHO, you get the best of all worlds. Corrosion resistance (same process Glock uses on their metal), accuracy (it is a treatment, not a coating, so bore size is relatively unaffected), hardness (it is surface-hardening, after all), and easy cleaning (it is a very slick surface). I would pick this one, hands down.

ETA: Corrected for stupidity...

 

[MrSpiffy]

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.

 

[badkarmamib]

Whoa, how did that happen? I must have been tired when I was typing, sorry for any confusion on that one. Fixed to save confusing the next person...

 

[lysanderxiii]

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.

 

[Casefull]

Thanks for explaining the chroming process in detail. Obviously not the negative the internet experts make it out to be.

 

[Ibmikey]

Nitride is the only way to go if you intend to keep the rifle for a long time and shoot it often, will that process be more accurate? Maybe a little better than chrome lining and the same as phosphate but in reality you are not going to notice the difference as a plinker or protection arm.

 

[MrSpiffy]

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.

Thanks for explaining this in detail. I didn't realize this is how they plated barrels. This is great information to know, and as an engineer I love to learn about this stuff.

 

[GunnyUSMC]

I remember the AR Fanboys on other forums with their nursery rhymes. Chrome will get you home and Go chrome or go home. This was just a few years ago when Nitride barrels started hitting the market at prices from $100 to $150. Most of the ones putting down Nitride didn't even know what Nitried was. All that they knew was the Nitried barrels were cheaper so, they weren't as good as the chrome lined barrels.
Most barrels are made from Chrome Moly Vanadium Steel. If you get one that is Chrome lined most often it will have a Phosphate finish on the outside. Nitried barrels are treated inside and out. Now don't forget that there are Cryo treated Phosphate barrels also. And there are stainless steel Nitried treated barrels also.
Most of the barrels I use are Nitried treated. I have used stainless steel and Nitried treated stainless steel. I did use a Cryo treated barrel on a build for my brother in law. I'm still waiting on word from him on how it shoots.
When I use a barrel with a Phosphate finish, I like to coat it with Aluma Hyde II for better protection.
Last year a friend wanted a to build an AR with a 15 inch rail but didn't have a lot of money to spend. We bought a complete upper kit from Delta Team Tactical that came with a Nitried barrel for $260. He now has over 2000 rounds through it and it still shooting good.

When it comes to picking out a barrel for a build, pick a barrel that will fit your needs.
I think I have found the barrel for my next build.
1 in 7" twist Pencil Profile 4150 VChrome Moly Vanadium Steel Barrel, Nitride Finished Mid-length Gas System .625 diameter at the gas block.

 

[Coal Dragger]

I have two barrels that are salt bath nitride finished, both Daniel Defense cold hammer forged 18" S2W contour 1:7" twist, and made of chrome moly vanadium 4150 steel, which is the tougher machinegun rated ordnance steel. One came on a complete DD rifle, the other I bought to replace a chrome lined barrel that had a poor lining job and the chrome flaked out (CMMG junk). Both are easy to clean, and have been 100% reliable for extraction and feeding. Both have been very accurate, particularly with heavy bullets.

I also have one really good chrome lined barrel on a Colt M4A1 carbine that is the new M4A1 contour. Uncle Sugar finally figured out that the old government profile barrel was stupid, and they came up with the excellent M4A1 contour which is a true medium contour and shoots a hell of a lot better than the previous government profile. This barrel is also made from CMV 4150 steel, button broached to a 1:7" twist and has chrome lined bore and chamber (not to be redundant). Using good quality ammo it keeps up with my other two nitrided barrels in the precision department. Colt seems to be capable of making a very good barrel, this one has given me sub MOA 10 shot groups with 69gr SMK hand loads. Cleans up easy, and is 100% reliable.

Both methods greatly increase barrel longevity all else being equal. Both are totally acceptable. Pick whichever you like, I'm more concerned about the quality of the barrel materials, and manufacturing quality standards and procedures prior to plating or salt bath. A good dimensionally acccurate barrel made from good steel, cleanly gun drilled and polished before rifling, properly stress relieved, and heat treated, will be good as long as the plating process for the chrome lining is good or the salt bath process is good.

I'm so pleased with both I'd love to see the two processes more widespread among sporting rifle barrels in other categories. A good carefully made CMV 4150 nitrided or chrome lined barrel could make a lot of sense for some of the big over bore magnums to give more acceptable barrel life. In fact if memory serves SAKO used hammer forged chrome lined barrels for their TRG 42 in .338 Lapua.