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I've been thinking about this in regards to BCG coatings/treatments and their durability. Apples to apples. Same quality level of the components, consistent heat treat, etc.
Phosphate is probably the least durable of the coatings, but mil spec BCGs are chrome lined. Which will enhance durability in those areas. I don't know of phosphate BCGs without chrome lining of the bolt carrier. Perhaps there are bottom of the barrel BCGs that are phosphate without being chrome lined, but that's not relevant if we're talking about quality parts.
Nitride is a great surface treatment. It is very durable and corrosion resistant and the finish is applied to the entire BCG. Making the BCG more wear resistant and easier to clean. However, it lacks the chrome lining in the carrier, which may make it less wear resistant in that area.
There's also nickel boron, which seems to me to fall somewhere in between chrome and nitride. Some lower quality NiB BCGs have had the coating flake off, but again, low quality or defective parts are not good for comparison. It does seem to be the best of both worlds, but I suspect it is not as durable as the chrome lining or fully chromed BCGs.
There are also other coatings and treatments. Fully chromed BCGs, which are very durable, but also expensive in comparison. There are also QPQ, titanium nitride and other variations. Which seem to be close to nitride finishes in durability and other properties.
While coatings other than phosphate have definite advantages, I'm not sure how much of an advantage they are overall. I don't think a nitride BCG is going to be as durable as the chrome lining of a phosphate BCG. So while the phosphate BCG's surface may wear, the chrome lining where it contacts the gas rings is likely to outlast the nitride.
In any case, I'd rather have a high quality BCG that's worn down to bare metal from use than one with a more durable surface but unknown heat treat and QC processes. The most likely failure seems to be shearing a bolt lug or breaking a cam pin, which the coating has nothing to do with. I'm skeptical of a lot of the claims in regards to lubrication. Claims that because of the surface it can be run without lubricant. It seems that regardless of the properties of the BCG, proper lubrication will always be better than none, even if it
is possible to go without.
In my opinion, I don't see a lot of reasons to spend much more than what it costs for a good quality mil spec BCG. In a lot of cases, the nitride BCGs seem to be coming in under the cost of a phosphate mil spec these days. Probably due to the lower cost of this type of metal treatment compared to chrome plating.
So which type provides the best performance or best price/performance, with all else equal? No wrong answers. I think the only wrong answer would be sacrificing overall quality for a certain type of BCG coating. If some of my opinions or information is way off, I'm interested to hear why.
Phosphate is probably the least durable of the coatings, but mil spec BCGs are chrome lined. Which will enhance durability in those areas. I don't know of phosphate BCGs without chrome lining of the bolt carrier. Perhaps there are bottom of the barrel BCGs that are phosphate without being chrome lined, but that's not relevant if we're talking about quality parts.
Nitride is a great surface treatment. It is very durable and corrosion resistant and the finish is applied to the entire BCG. Making the BCG more wear resistant and easier to clean. However, it lacks the chrome lining in the carrier, which may make it less wear resistant in that area.
There's also nickel boron, which seems to me to fall somewhere in between chrome and nitride. Some lower quality NiB BCGs have had the coating flake off, but again, low quality or defective parts are not good for comparison. It does seem to be the best of both worlds, but I suspect it is not as durable as the chrome lining or fully chromed BCGs.
There are also other coatings and treatments. Fully chromed BCGs, which are very durable, but also expensive in comparison. There are also QPQ, titanium nitride and other variations. Which seem to be close to nitride finishes in durability and other properties.
While coatings other than phosphate have definite advantages, I'm not sure how much of an advantage they are overall. I don't think a nitride BCG is going to be as durable as the chrome lining of a phosphate BCG. So while the phosphate BCG's surface may wear, the chrome lining where it contacts the gas rings is likely to outlast the nitride.
In any case, I'd rather have a high quality BCG that's worn down to bare metal from use than one with a more durable surface but unknown heat treat and QC processes. The most likely failure seems to be shearing a bolt lug or breaking a cam pin, which the coating has nothing to do with. I'm skeptical of a lot of the claims in regards to lubrication. Claims that because of the surface it can be run without lubricant. It seems that regardless of the properties of the BCG, proper lubrication will always be better than none, even if it
is possible to go without.
In my opinion, I don't see a lot of reasons to spend much more than what it costs for a good quality mil spec BCG. In a lot of cases, the nitride BCGs seem to be coming in under the cost of a phosphate mil spec these days. Probably due to the lower cost of this type of metal treatment compared to chrome plating.
So which type provides the best performance or best price/performance, with all else equal? No wrong answers. I think the only wrong answer would be sacrificing overall quality for a certain type of BCG coating. If some of my opinions or information is way off, I'm interested to hear why.
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