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Posted: 9/24/2002 6:42:57 PM EDT
Which is more resistant to corrosion? A bolt/bolt carrier that is hard chromed and is dry (no CLP) or a parkerized bolt/carrier coated with a light coating of CLP? I know the hard chrome will wear the upper reciever more but I just want to know if its more corrosion resistant in the old Vietnam era coating.
Link Posted: 9/25/2002 7:21:35 AM EDT
Here is a link to a metal finishing company. They discuss the properties of a huge number of finishes and address corrosion resistance. They give the nod to parkerizing over chrome.

toccoametal.com/plating.html

Link Posted: 9/25/2002 1:04:07 PM EDT
That webpage talks about decorative chrome not hard chrome.
Link Posted: 9/26/2002 6:03:49 AM EDT
According to Armaloy. who does hard chrome for finishes, hard chrome meets the ASTM-B117 standard (5% salt spray at 95F for 12 hours).

Depending on the type of parkerizing process and the metal it is applied to, parkerizing can stand up to the same ASTM-B117 test for 1,000 hours. I believe mil-spec parkerizing is a manganese phosphate (DoD-P-16232 Type M is the spec for M16s). This site shows that finish as lasting 168 hours under the ASTM-B117 test.

If you want to do more research on this, there is lots of info available on Google; but I'm pretty sure parkerizing will beat any type of chrome - decorative or hard for corrosion resistance.
Link Posted: 9/26/2002 8:17:37 AM EDT

If you want to do more research on this, there is lots of info available on Google; but I'm pretty sure parkerizing will beat any type of chrome - decorative or hard for corrosion resistance.


Not being a smart ass, I really am curious here, but why not parkerize the chamber and bore instead of chrome lining if that's the case?
Link Posted: 9/26/2002 11:56:17 AM EDT
[Last Edit: 9/26/2002 12:06:39 PM EDT by Bartholomew_Roberts]

Not being a smart ass, I really am curious here, but why not parkerize the chamber and bore instead of chrome lining if that's the case?


Good question and one I don't know the answer to; but I bet it has something to do with the hardness, adhesion and lubricity of chrome.

Just guessing mind you, but I imagine that a copper 55gr bullet traveling at 3,200fps would make whatever interior coating you used irrelevant unless it was harder than the bullet. Otherwise wear would scrape it down to bare steel in no time.

Of course, I might just be wrong as well; but I don't think I am on this one. Here is a picture of a bearing in a thin coat of hard chrome after 24 hours of the ASTM-B117 salt spray test.

Edited to add:

I've found a few hard chrome coatings that appear to last 100-200 hours in the ASTM-B117 salt spray test. The main factor seems to be how thick the hard chrome is applied, what type of chrome alloy is used and the surface it is applied to - so its possible some hard chrome would beat parkerizing.

The stuff offered by Armaloy porbably doesn't since they compare it to 440C stainless steel, which shows rust by 24 hours in the test.
Link Posted: 9/26/2002 2:25:24 PM EDT
Well I have been doing some research and I also have some first hand experience with hard chrome. I was none too impressed with Armoloy. I had S&W revolvers in .357 Mag, .41 Mag, and .44 Mag I hated the cleaning process I had to go through after shooting and thought hard chroming would help so I had em all Armoloyed. But the vapor honing that Armoloy does just gives grime a place to hold on to. If I didnt clean every tiny crevice it would rust (not bad though) and any where it wore due to friction it would self polish bright spots. I am no fan of revolvers or Armoloy and I sold em all. I even sold the nickle plated 686 because I didnt like the bright shiny nickle even though it never rusted.

As for chrome there is 3 types. There is thin film coating. This is whats done on top of nickle to help get rid of nickles yellowish cast and does not help much at all. Then there is a "flake chrome" like whats used in chrome lined pistons. The surface looks like the desert (cracked and flaky) and is designed to hold oil well but is not good at resisting corrosion. This is the type that wont stop corrosion you cited. Finally there is a 100 hour salt spray even thick coated hard chrome. This is what I want to use.

My idea is this... I am going to hard chrome EVERYTHING in my upper and lower recievers. Bolt/carrier, trigger group, mag release assembly, bolt catch assembly, and an ambi safety. This will make it more corrosion resistant than the raw steel as well as giving it less friction. Then I will coat in a Teflon or Moly based finish to make it all black again, make it impervious to corrosion and add lubricating qualities to make it quick to clean up. The parts that rub together will eventually be the only parts that have exposed hard chrome. This will be better than the normally exposed steel after the parkerizing wears away since its more corrosion resistant and slicker. The rest of the parts will be maintenance free (not need to be protected to stop rust) and I can use a minimum of non-particulate accumulating lube on the parts that rub together to stop the buildup of carbon and dust thus improving reliablity.

As far as the chrome lined bolt carrier wearing out the upper reciever after the Teflon/Moly finish has worn away, I will have a moly dry lube on the upper reciever to help slow this and even if it does wear it out its not an expensive part and it wont wear out before my barrel so I will just get a new upper reciever when it time to replace my barrel so its a non issue to me.

What do you guys think? I know its expensive but my preban is only half way built up and I already have over $2000 in her. I expect it to go past the $4000 mark by the time I am done. I just have one simple goal... To creat the ultimate AR. Cost be damned!
Link Posted: 9/26/2002 10:13:24 PM EDT

Originally Posted By DevL:
What do you guys think? I know its expensive but my preban is only half way built up and I already have over $2000 in her. I expect it to go past the $4000 mark by the time I am done. I just have one simple goal... To creat the ultimate AR. Cost be damned! hr


I think that sounds like a really cool science project :) Wish I had the cash for something like that! If you end up getting that done, it would be interesting to see if your theory is borne out in practice.
Link Posted: 9/27/2002 6:06:02 AM EDT
I'm with Ryan, I'd sure like to know what the results are.

I guess I'd be concerned with a few things in your experiment though:

My main concern would be function afterwards. A layer of chrome and then a layer of a teflon or moly finish is going to make tolerances much tighter. Will it effect reliability and function?

You'd be hard chroming aluminum and steel. Will the hard layer of chrome over the softer aluminum be a problem? Also, I think the aluminum receivers are hard anodized anyway prior to the manganese phosphate parkerzing and may be superior to your proposed coating in corrosion resistance.

Finally, the AR15 is a machine. Its not just a single part but a system of parts that are all designed to work together - and the parts are designed based on certain assumptions and standards used to build them. You are proposing to significantly alter those standards. How is that going to affect the system as a whole to see less friction (increased cyclic rate, harder recoiling bolt?) and extra thickness internally?

What you propose might be a better AR; or you might just be trading one set of problems for a different set. Tough to say; but I'd sure be interested in how it works out for you. So if you do decide to do it; I bet we would all appreciate regular reports on the project (and not just immediately afterwards but two and three years down the road as well)
Link Posted: 9/27/2002 6:49:59 AM EDT
Im not going to touch the upper or lower receivers themselves. They are retaining the hard anodized finish. The parkerized parts are the steel internals and the barrel. The barrel I will leave alone. Its already chrome lined and the phosphate finish is tough and easy to keep coated with oil and rust free. There is no park on aluminum its a physical imposibility. To chrome aluminum requires a coating of copper first then nickle then chrome... not going there. I intend to fire 200 rounds through the gun first to get it broken in then pull the guts and have them refinished. The moving parts are what I am concerned about here. Before I have the Colt upper barreled I will be spraying it with Perma Slik to give it the same internal lube as Bushmaster uppers have. Then after 200 rounds the rest of the parts get done. I still need to find out which coating will be the toughest... I dont want to have a soft outer coating on the mag realease, trigger and bolt release to the point that my finger rubs it off and shows bare hard chrome underneath. So far I have found that both Accurate Plating and Weaponry and Tripp Research both do coatings on top of hard chrome in firearms. Accurate plating appears to do this "standard" while its a special order job and more expensive through Tripp Research.

I am leaving all external parts alone. My FF RAS is aluminum and already is hard anodized. Same goes for everything else going on it. ACOG scope, Surefire M900 both are mil spec hard anodized. The outside of the gun is getting left alone. because these coatings are somewhat soft and I dont want them to be exposed to any rough handling the outside of the weapon might see. The point is to need less lube inside the gun thus allowing less fouling to accumulate and getting a rifle that holds up to rough conditions and infrequent cleanings better and is also easier to maintain.
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