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9/19/2017 7:27:10 PM
Posted: 5/2/2004 8:09:51 AM EDT
Are these silver or do they have a black coating over them?
Link Posted: 5/2/2004 8:14:52 AM EDT
They are silver....and are known to have issues.
Link Posted: 5/2/2004 9:59:35 AM EDT
What kind of issues? I bought one off e-bay and it was black not silver as listed in midway's catalog so I emailed them and they said it was chromed which I believe now was wrong but it was cheap enough that I was going to keep it until you started talking about issues so now I gotta know what issues?
Link Posted: 5/2/2004 10:14:44 AM EDT

Originally Posted By TOM64:
What kind of issues? I bought one off e-bay and it was black not silver as listed in midway's catalog so I emailed them and they said it was chromed which I believe now was wrong but it was cheap enough that I was going to keep it until you started talking about issues so now I gotta know what issues?



I was going to buy a DMPS bolt and Carrier too, I am also curious to hear about its "issues"
Link Posted: 5/2/2004 11:35:59 AM EDT
I believe their carriers are OK. I do own one and it's working just fine.

Unfortunately, over the past four years or so almost every report (on arfcom) of a bolt breaking in half through the cam pin hole has been a chrome DPMS part. Almost every "victim" contacts DPMS, sends the broken part back and gets a new replacement part. However, they don't seem to be fixing the problem, just recovering the evidence and never telling the buyers why they broke.

I suspect it's the result of metalurgical condition called hydrogen embrittlement. This is an easy condition to correct but requires baking the parts for a day or so at controlled, elevated temperatures. Perhaps they don't want to spent the extra $ to get rid of this problem.
Link Posted: 5/2/2004 12:01:53 PM EDT
So is it just their chromed parts or all of their bolts and carriers?
Link Posted: 5/2/2004 1:36:42 PM EDT
I use a DPMS chromed carrier in one of my rifles and have has no issues with it. I do not however use a chrome bolt and probably never will unless i get enough dough to buy one of thos LMT enhanced ones.
Link Posted: 5/2/2004 1:58:22 PM EDT
In order to chrome, the bolt has to be submerged in acid. Acid is sometimes not removed completely, and remains under the chrome. The steel is weakened, you fire the rifle, and the result is ugly. Real ugly. I saw it happen at the range, I took the chrome bolt out of my varmint rifle that day, never looked back.
Link Posted: 5/2/2004 2:23:12 PM EDT
H8MTV is partially correct. It isn't really acid trapped under the chrome.

The hard chrome plating process has one dip cycle before the plating is applied where the part is emersed in a sulphuric acid solution. Sulhuric acid has an excess of hydrogen atoms that bond with other atoms in the chrome-moly steel alloy from which the parts are machined. Rinsing the acid off the part gets rid of the acid but not the bonded hydrogen atoms. These hydrogen atoms tend to made the part REALLY hard near the surface which under stress cause the part to essentially be less "flexible". Under load the part breaks rather easily.

The process called "Hydrogen Embrittlement Relief" involves baking the finished parts in an oven for up to 36 hours. This heating breaks the hydrogen atoms loose and they are quite simply released into the surrounding atmosphere and are no longer part of the base material. Thus the design properties of the selected allow return.

This whole process will occur naturally, but at room temperature it takes years. Once the parts is stressed it's too late, the failure is imminent depending on the applied loads.

H.E. does not generally occur with phosphated parts. The black manganese phosphate process doesn't use sulphuric acid dips.
Link Posted: 5/2/2004 3:41:45 PM EDT
Ok so set me straight, a phosphated DPMS bolt and carrier are ok it's just the chromed parts that have issues? Also if mine is black it is not chromed right?

Sorry for all the trouble.
Link Posted: 5/3/2004 9:38:08 AM EDT
After rereading the discription on the bolt carrier it says chrome lined and it is chrome lined where the gas rings go so this was my mistake and all is well now cause after reading these responses I don't want a chrome bolt, thanks guys for the info, this site is great.
Link Posted: 5/3/2004 1:15:14 PM EDT

Originally Posted By TOM64:
Ok so set me straight, a phosphated DPMS bolt and carrier are ok it's just the chromed parts that have issues? Also if mine is black it is not chromed right?

Sorry for all the trouble.



Yours is not chromed.
Link Posted: 5/3/2004 1:44:27 PM EDT
Chrome lined good, chrome plated bad. No trouble, thats what the site is for, I learned something in this discussion, thanks guys.
Link Posted: 5/3/2004 5:45:25 PM EDT
Many aircraft parts and even the front wheels of semi-trucks are not allowed by law to be chrome plated, due to hydrogen embrittlement. The previous post is correct, it weakens the steel surface.
A hard chrome carrier is fine, easy to clean, pretty, and not taking near the stress of a bolt. I too, immediatly replaced my hard chromed bolt with a mil-spec black (manganese phosphate) bolt. It was one of my first builds and luckily the "Smith enterprises" hard chrome carrier and bolt was having problems, it turned out to be a short extractor groove. But after thinking back to my chrome and gold plating days, I remember my old boss explaining Hydrogen embrittlement to me and I decided on my own to use a plain old black bolt...the only way to go!
Link Posted: 5/4/2004 12:03:30 PM EDT
So do people like LMT Bake their bolts before they sell them to get rid of the hydrogen?

What about getting a DPMS bolt and carrier and baking it yourself before you use it. Would this do the same thing?

JErad
Link Posted: 5/4/2004 8:14:56 PM EDT
I would ask DPMS if they would give you a chrome carrier and black bolt combo at a discount, they would probably do it, and you would much safer for doing so. DPMS is not the only AR company that has had chrome bolts crack in half, I know so personally, and it is a potentially lethal situation. I would NEVER use a chrome plated bolt, baked, broiled or otherwise.
Link Posted: 5/5/2004 3:03:26 AM EDT
That's the way my DPMS M4gery came. Chrome carrier and a black bolt. So far no problems at all...but I've only put about 125 rounds thru it...
Link Posted: 5/5/2004 5:21:25 AM EDT
I have an old Colt made chromed Bolt laying around,
IS IT SAFE TO USE ?
Did Colt mfr. these correctly?
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