best AR-15 barrel coating

You don't.

Get stainless or carbon steel.

You don't.

Honestly, I think chrome lined bores are starting to be a little passé.

You get very similar benefits from the various nitride treatments, without the side effects. Similar longevity, better accuracy, lower cost.

My go-to rifle is just plain stainless steel, so I wouldn't even say you need the fancy coatings. The only major benefit of chrome lining is with continued heavy fire. If you're dumping mag after mag frequently chrome may be of benefit.

It was used as a durability measure in full auto pencil bbl M-16s.

If you frequently spend the night in a wet and humid place, like a jungle, you might need that chrome chamber so the verdigris doesn't "weld" the cartridge into the chamber and cause problems, and like was said might be some advantages to chrome for full auto, but I'm not sure about that. Stainless is a very good choice. Harrison at ARP uses and advocates for melonite coating in his barrels. I don't have one but know those who do hold them in high regard. I do have a barrel with the melonite coating, on a couple of barrels and they have shot very accurately. Word on the street has always been that stainless will shoot more accurately than chrome, because the chrome plating process might not be consistent coating the barrel and that's not the problem with stainless. The most accurate AR I've ever had was stainless.

Nowadays, almost all military rifles are universally chrome-lined to protect the rifle barrel from excess erosion. AR-15 rifles are particularly prone to erosion when fired rapidly, in part due to the high velocity of the round, and in part due to the high pressures generated by the cartridge.

416 stainless steel. Already had the "chrom"ium in it.

Hard chrome is much more durable than any stainless alloy

army_eod said:

Hard chrome is much more durable than any stainless alloy

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That is true. But chances of the average Joe shooting enough to see the difference is low. I'd prefer nitrited treatment on the 416r. That would give the case hardening and rust resistance. The plus side of 416r is the machining part of it. Easier to have uniform cuts. But that's all my opinion.

Of my 6 separate 5.56 AR rifles, two have chrome lined barrels. The rest, and my 7.62x39, don’t.

Since I’m not living in a swamp or dumping magazine after magazine I haven’t noticed a difference. Neither will the vast majority of AR owners.

To a lot of newer gun folks, the gun shop counter and forum talk sent your way about what you have to have for a pistol or AR is a lot of opinion told by people who got their info from the same places... Internet forums and gun shops. Take it all in not as verbatim gospel, but rather as nuggets of info that you can use and compare to your own experiences to as you learn and gain knowledge.

Good luck with your search.

Stay safe.

Because its "TACTICAL"!

OP. No.

Melonite.

I wouldn't use a rifle with a bare steel barrel for home protection, unless it was a stainless steel barrel. Chrome, nitride, whatever.... I just want some sort of corrosion protection.

If you have to shoot someone with your rifle you've already won the "really horrible day" lottery, so I wouldn't want anything else to go wrong either.

joker1969 said:

why DO I need a chrome barrel/chamber for my home defense AR-15

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My home defense AR has a nitride finish on the barrel. Maybe not quite as good as chrome lined CHF but 99% of users will never notice a difference. Stainless does wear faster from what I understand but I would also bet most AR owners would never wear out a stainless barrel either. I have a Model 7 with a stainless barrel and I consider wear a non-issue with it but it's a hunting rifle so it'll never see a high round count.

Nitriding likely is even better than chrome for bores, both mechanically and chemically.
Mostly, such linings are to help prevent corrosion and/or wear in the barrel in adverse (read military) conditions.
Is that necessary for a home defense weapon?
Not necessarily.
However, if there's no price point difference, there is no reason to deselect a rifle for having a lined ore.

Nitride/Melonite. I became a believer after reading the instructions with my piston kit regarding carbon build up on the surface of the barrel, "Scrape it off with a sharp object such as a knife or scraper." I did tentatively and then with gusto, no harm at all to the finish on the barrel. SOLD!

Next test was trying to drill through it.

This was for an upper dedicated to eating several cases of corrosive 7n6 5.45x39. Since then, I opt for nitride barrels every time.

joker1969 said:

(What is the) best AR-15 barrel coating?

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Carbon over a light coat of copper, because that means you've been shooting it.

Skip coatings until you have a reason not to, somewhere in your second 10k rounds fired.

CapnMac said:

Nitriding likely is even better than chrome for bores, both mechanically and chemically.

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Yep.

Unlike chrome, which is bonded to the steel, nitride is the steel, nothing can debond. Ever. Nitride gets into the high 60s Rc, so it's like having a tool steel barrel from a wear standpoint, but without the brittleness of a through-hardened tool steel part.

Same reason double heat treated carburized 8620 steel is used in bolt carriers, ring gears and other applications that require high surface hardness but also good fracture toughness.