Chrome versus phosphate bolt carrier and bolt

[Harvest123]

When I built my first rifle, 5.56, I ordered a Noveski barrel. Noveski folks were great to me. When I asked about a chromed BCG, the technician told me that the chromed bolt carrier did not hold on to oil nearly as well as the phosphate coat. Since I was not buying the BCG from him, it made no financial sense to lead me astray either way, and the guy was really cool to talk specs with. He seemed to know his business very well.

What is your opinion on the Chrome BCG and the military phosphate finish. So far the standard BCG has run like a top. Is there a reason for the chrome if the phosphate does stay lubricated better (or so I am told)?

[invisiman]

I am curious to find out what they say. I am getting ready to order a bolt carrier and bolt from AA to have an extra one.
They have two on there, the standard and chromed hard use ones. I think if it is chromed it is less likely to rust
under harsh conditions, but I am not sure. I know both of AA's bolts are excellent, but would like to know the difference between the two.
Please chime at any time....

[invisiman]

I just checked with AA about the two bolts. The gentlemen told me the upgraded hard chromed one is also Ion Bonded. Very nice.

[LRRPF52]

The original Armalite AR10 and AR15 rifles used a complete hard chrome bolt carrier group. The only part not hard-chromed on the Colt Model 601 was the Bolt Cam Pin.

All bolt carriers are chome-lined on the inside of the bolt recess, which is basically a floating cylinder for the piston (bolt). The inside of the carrier key is hard chromed as well on Mil-Spec guns, and the tolerances have to be very exact. If they deviate on the large side, you have short-stroking. If they fall on the tight side, the flange on your gas tube will get worn eventually, which will cause short-stroking.

I use both chrome and milspec manganese phosphated (Parkerized) carriers. On both of them, I polish the raceways (4 total), which are the only contact surfaces of the inside of the dry film-lubricated 7075 Aluminum upper, hard coat anodized (Type III). I use Slip2000 EWL as lubricant, which has great viscosity, but is quite thick as well, so it has more lasting effect than CLP/Break Free, and other thin lubricants.

With the chrome carrier, when in a worst-case scenario with all the lube burned off, it still has great surface lubricity, especially when the raceways are polished. If the Parkerized carrier burns off the lube, it still has great surface lubricity on the polished raceways.

The area that really absorbs liquid lubricants is the anodized aluminum.

In the end of the analysis, the chrome carrier offers more corrosion resistance in high humidity climates, leading to longer service life of a critical operating part. If I lived in the South East United States, East Coast, or any high-humidity climates, I would lean towards a chrome, Nickel Boron, or Titanium Nitrided carrier. I have been running tests on all 4 types, and I like the buttery smooth surface of the NiB carriers a lot.

In any option, I polish the raceways, so reliability based on surface lubricity and ability to hold oil is the same. Another key thing to do is always keep your Bolt Carrier well-lubricated, and the gun will run. It takes a bit of repetition in the early stages of breaking in a new blaster to get the lubricant embedded into the metal surfaces that contact each other, and 100% reliability can be expected during that initial process, as long as sufficient lubrication is applied to a properly-built gun.

[ericv]

Excellent and interesting explanation, thank you

How would using Cerakote on the BCG figure into this equation?

Eric

[LRRPF52]

I have tried Cerakote, and it adds too much surface thickness for my tastes, and galls with friction. I think Cerakote does best as an external firearms finish, but not as an articulating mechanical parts coating.

[kamrr4437]

I guess the phosphate being a little more porous would hold oil a little better. Chrome would be slicker so i could see where there would be fact in the oil not adhering to it as well. But you can clean up a Nickel Boron or a Chrome carrier up so much easier. And i dont really plan on going into battle and running 4 to 500 rounds full auto in a battle situation. I dont think in normal practical usage whether it be hunting, going to the range or defending from zombies you would have a problem with either finish. But as LRRPF52 says lube is important. A well lubed AR is more critical or crucial than a clean AR.

[LRRPF52]

A carbon-fouled AR runs better than a white-gloved AR. Carbon fouling on the bolt tail especially, leads to better gas seal. We were pounded and pounded with the BS that we had to have immaculately clean weapons in the military, while someone forgot to tell that to guys in units where they burned 500+ rounds a day, and detail-cleaned once a month, while lubing generously.

I figure all the white glove inspections I did for 10 years in Infantry units is enough to carry over to my personal blasters, so I just keep them lubed with Slip2000, and blast away.

[pinzgauer]

A carbon-fouled AR runs better than a white-gloved AR. Carbon fouling on the bolt tail especially, leads to better gas seal.

Curious how carbon on the bolt tail results in a better gas seal? All the input I've seen was that carbon on the bolt tail worries folks, but essentially has no impact as it's in a non-critical area. I may have to go study the exploded views again.

The word from the armorers/mfg's/hard use crowd on M4carbine was that Colt went to phosphate on the BCG as it retained oil longer, and wore less when dry. I had always assumed it was a cost savings measure, but it probably cost more to selectively chrome the inside of the carrier and not the outside.

There are carbines pushing 20k rounds without cleaning in extended tests. On my son's M4gery 5.56 (J&T) and my Grendel carbine we've been using the 2 drops of CLP in the bolt holes lube approach, which keeps them quite wet. I'm probably several hundred Grendel rounds down range w/o interior cleaning, and 1500+ 5.56 including much dirty wolf/tula 5.56. They run like champs. We keep an eye on the barrels, bore snake them periodically.

The only place we ever see carbon buildup is on the tail.

But run them wet and even when dirty a properly spec'd AR works great. It still makes sense to keep an eye on the wear areas, but even with just "2 drops in the bolt holes & cycle" lubing, the inside of the action stays lubed.

The Marines & Army are both starting to see extended wear from running carbines too dry, and also from loss of the phosphate coating from scraping with dental tools, etc due to the white glove mindset.

Lot's of love for "Froglube" in the sandbox apparently. Goes on wet, then dries a bit at room temp. But sticks rather than running off. Guys who can use anything are saying really good things about it it in the real world. I've not tried it, but a LGS is now carrying it so I might try. Does not take much, so a small bottle last a very long time.

[LRRPF52]

Think about the carbon acting as a gasket inside the chamber formed by the bolt tail, flange for the gas rings, and the bolt carrier. The more build-up, the less chance of leakage.

[VASCAR2]

I bought some of the Froglube paste and so far I really like it.