Is the gas chamber chrome lined?

[CJW]

Is the gas chamber inside the BCG chrome lined?( the area that the bolt slides back and forth in)

Thanks,
Chuck

[A5BLASTER]

None if mine are chromed lined.

I have bcg's from PF and righttobeararms.

[LRRPF52]

Per Mil-Std it is supposed to be.

The inside of the carrier key is supposed to be hard chrome-plated as well.

The dimensions inside the carrier, materials for the carrier and the key, and processes are all called out in the Technical Data Package.

The civilian market is filled with components in these areas that are made by companies who may or may not be aware of these call-outs, many of whom couldn't care less as long as they are filling orders.

There are 3 critical Internal Diameter dimensional call-outs inside the bolt carrier.

The first is the largest opening that allows the bolt to enter the carrier bore.

The second steps down from that ID, compressing the gas rings inside the gas ring flange.

The third is where the bolt tail articulates in and out of. If it is too large, the gas will leak back into the action and down into your fire control group.

A true Mil-Spec bolt carrier and key has many call-outs that when held-to, provides for an extremely reliable AR15 Stoner internal expansion operation system.

If one of these call-outs is out of spec, it can lead to short-stroking and unreliable action.

The carrier key is supposed to be made from much softer steel alloy, then internally hard-coated with chrome. This is so it doesn't win the hardness war with the gas tube flange early, and render the gas tube flange smaller, causing gas leakage and unreliable action. I've seen that happen on 20" Vismod guns more than anything else, since the flex in a 20" RLGS gas tube allows more play and opportunity for mis-alignment when assembling. CLGS and PLGS are the most rigid down on the opposite end, so when properly aligned, they won't clip on you inside the carrier key usually.

Another problem is that many of the BCGs cranked out over the years had mediocre carrier key fastening and token staking on loosely-torqued fasteners, leading to looseness and immediate gas leakage, short-stroking half-o-matic Vismod-15s.

Another problem is imitation gas rings on the bolt, as well as rough tool marks inside the carrier bore for the bolt. As the cheap gas rings grind back and forth against the tool marks, it shreds them to crap, even busting them out of the gas ring flange and into the carrier. You'll see little pieces of gas rings flaking out inside the BCG.

Parts are not created equally.

[CJW]

Very interesting...

[Kswhitetails]

I have heard of carriers that weren't chromed, but I've never personally seen one. A5, you sure about yours?

[A5BLASTER]

I have heard of carriers that weren't chromed, but I've never personally seen one. A5, you sure about yours?

Perrty sure. I have had all of mine apart. I like to tinker case y'all didn't know lol.

Unless it's under the black surface coating there is no chrome in any of my rightobear lowmass bcgs, my PF bcg are my nickoleboron coated full mass (can't remember who it's made by)

[Kswhitetails]

Interesting. I'm not sure if there's a coating that would stick to the chrome, or if they remove it to treat a bcg. I'd be surprised to hear that if they do. I don't have any fancy BCGs, I've got two BCM, a PSA, a Joebobs, and a LaRue. All of them are chrome lined. I've resisted the draw to the fancier treated versions as I don't think I could ever shoot enough to wear out a standard M16 Mil spec version.

[A5BLASTER]

Interesting. I'm not sure if there's a coating that would stick to the chrome, or if they remove it to treat a bcg. I'd be surprised to hear that if they do. I don't have any fancy BCGs, I've got two BCM, a PSA, a Joebobs, and a LaRue. All of them are chrome lined. I've resisted the draw to the fancier treated versions as I don't think I could ever shoot enough to wear out a standard M16 Mil spec version.

I will say this a properly done nickoleboron coated bcg will blow your mind how clean it stays and how slippery it is in the rifle.

[Old Bob]

NiB outperforms chrome in wear resistance & has a better co-efficient of friction. So, the inside of the NiB BCG wouldn't need chrome plating.

[Kswhitetails]

That would make sense. Same for the PVD versions I'd assume.

[stubshaft]

I just got a BCG from righttobear and the gas chamber appears to be only nitride coated.

[LRRPF52]

I have heard of carriers that weren't chromed, but I've never personally seen one. A5, you sure about yours?

There are multiple bolt carriers on the market that don't have Mil-Spec Hard Chrome-Plated bores, and I own several of them.

The different options on the market include:

* ROBAR NP3 (PTFE-Teflon)
* Titanium Nitride (TiN) coated
* Nickel Boron plated (NiB)
* Nitrided (Salt bath quench polish quench)
* Polished Stainless steel
* Ion-bonded / Physical Vapor Deposition (PVD)
* Nano Composite Coatings (NCC)





A lot of these coatings and surface treatments have been around for decades, used in gear boxes, tool heads, high-friction aviation parts, and military-tested firearms components that were usually not adopted.

Everything is a trade-off.

Hard-chrome plating is hard to get right when looking at holding critical dimensional tolerances, yet the US and Canadian militaries specified that process for the AR15 family of weapons.

We did some testing comparing the performance of TiN, NiB, and Mil-Spec carriers over several years in Arctic and Sub-arctic conditions.

No performance differences were noted. NiB and TiN get permanently discolored when exposed to hot carbon gases, but this doesn't seem to affect performance.

Once source of BCGs through Midway was garbage, with falling occurring before test-firing.

Most other NiB BCGs I've used have been fine, as long as they were WMD, FailZero, and the ones from PF.

I've been using a lot of nitrided carriers lately, as long as they pass my initial inspections, including bolt/gas ring resistance in the carrier bore.

[PVBoom]

So, while rooting through my AR parts I found a couple carriers and gas keys I bought at least 15 years ago.
They appear to be just phosphated. I need to take another look at the inside of the gas keys to see if they are chrome lined.

I was regretting they didn't have one of the more advanced modern coatings and was checking out prices and considering ordering something in TiN or NiB.

Then as I read about the coating types it occurred to me I could have them hard chromed. I did this with several pistols in the past.
I send an email to the guy who does this (Mahovskys Metalife in Grand Valley PA) and intend to go that way.
FYI: http://www.mahovskysmetalife.com/#c-jqo31ui4SwVj

Is there any disadvantage to having this done to the carriers and keys?
The bolts are monsters bought here.

[Klem]

With respect, that sounds like a lot of money and effort for something that is unlikely to be of any benefit.

[PVBoom]

With respect, that sounds like a lot of money and effort for something that is unlikely to be of any benefit.

If its of no benefit why are bolt carriers coated in NiB or TiN?

Its considered to reduce wear, increase lubricity and make cleaning easier.

As for the cost, he charges $155 for an entire pistol, which is a lot more work in terms of disassembly and assembly.