Being the new guy here, and having experienced this response myself, this time I get the opportunity to say, "Use the search button." ;)
Seriously though... a plethora of information already exists on the topic on this forum alone.
I will say that both hard chrome lining and nitriding (in some form or another) have been used on high stress components for a long time - racing pistons as one example of something other than a barrel. Two main differences I have gathered from my research are: 1) Hard chrome is applied on top of a metal, while nitriding is a process that hardens the outer layer of the metal (similar to anodizing aluminum). 2) Nitriding is very hard and maintains a very smooth surface over time. Hard chrome is very hard and develops microscopic cracks over time. This is less desirable in some applications but beneficial in others, as the cracks allow space for oil to collect to maintain lubrication over longer periods of time. I might use nitriding over hard chrome on applications that do not require or allow liquid lubrication, but I would give the nod to hard chrome for things like the inside of a bolt carrier, where oil is needed for lubrication and is not continuously pumped as it is inside an engine.
Agreed. Well, throat erosion kills barrels, and heat is the greatest contributor to throat erosion. This is why the jury is still out for me on whether I'm going with a Noveske chrome lined barrel on my current build, or having a Noveske stainless steel barrel nitrided. I have not been able to find any concrete evidence or reputable source that says nitriding has a higher heat resistance than hard chrome, or vise versa. :shout: (meaning, which one is most resistant to wear at the extreme temperatures present in the throat of the barrel under rapid fire)
You should probably quantify that for people... I've read that while nitriding penetrates deeper than the thickness of a traditional hard chrome bore lining, it is by no means "deep." I agree with you that it is probably not wise to nitride parts that see high impact stress (I personally would not nitride any part of a BCG).
Smith & Wesson