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Broken gas ring jam


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#1 OFFLINE   zoomy

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Posted May. 23 2018 - 08:04 AM

I was testing my new light weight AR-15 build when after the eight shot it jammed and would not go into battery. Despite using all known methods I was unable to pull the charging handle back.
I pulled both take down pins and pulle off the upper. I had to use an aluminum rod and hammer to knock out the BCG. The bolt was completely jammed. I removed the firing pin and cam pin and knocked out the bolt with a brass rod. Turns out one end of the front gas ring was pulled out of the groove.
This is a new Rubber City Titanium BCG. I inspected the bolt bore on the carrier and everything looked good.
What would cause this to happen?


#2 OFFLINE   Pepper

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Posted May. 23 2018 - 01:13 PM

I was testing my new light weight AR-15 build when after the eight shot it jammed and would not go into battery. Despite using all known methods I was unable to pull the charging handle back.
I pulled both take down pins and pulle off the upper. I had to use an aluminum rod and hammer to knock out the BCG. The bolt was completely jammed. I removed the firing pin and cam pin and knocked out the bolt with a brass rod. Turns out one end of the front gas ring was pulled out of the groove.
This is a new Rubber City Titanium BCG. I inspected the bolt bore on the carrier and everything looked good.
What would cause this to happen?

Faulty gas ring. Or, out of spec bolt or carrier. Your gas rings should give a fairly snug friction fit. Meaning, when you insert the bolt into the carrier, they should be snug enough to hold it in place fairly firmly, requiring you to pull on the bolt to get it back out. If it's a loose fit, they can be proud of the slot, and can get folded over. Check the diameter of your bolt, and the bore in the BCG too. If the bolt is too small, or the groove too shallow, it could force a gas ring up and out of the slot. 




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#3 ONLINE   MontanaLon

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Posted May. 23 2018 - 01:33 PM

Titanium and steel together are prone to galling unless you lube the snot out of it. The gas rings are sliding on the titanium and due to their different molecular structure the surfaces bind on each other.




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#4 OFFLINE   Longhair

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Posted May. 23 2018 - 02:06 PM

Titanium and steel together are prone to galling unless you lube the snot out of it. The gas rings are sliding on the titanium and due to their different molecular structure the surfaces bind on each other.

Sorry, but nope.

In fact, metals need to be sufficiently dissimilar to resist galling. And titanium is more than enough tougher and different from tool steel to work together just fine.

Don't believe me? Just try to cut a piece of titanium with a file (hardened tool steel) and see what happens.

 

As an example, I offer the history of the original AMT Hardballer. The first ones used the same stainless alloy for the slides as the frame, and they had terrible galling issues.

 

The required difference doesn't have to equate to much, as long as one is harder than the other.




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#5 ONLINE   MontanaLon

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Posted May. 23 2018 - 02:33 PM

Stainless steel in some formulations are more likely to gall than others. Some are closer to bubble gum in how willing they are to stick to each other. It isn't the hardness of the metal that causes the issue but the molecular structure and titanium is very susceptible because of the structure. A file won't cut it because it is very hard but it will gall almost as bad as aluminum because they are similar in molecular structure. The hardness is only tangentially involved because hardened steel has a very different molecular structure which is very resistant to galling. 

 

Either way, without lube it will continue and likely get worse. 


Edited by MontanaLon, May. 23 2018 - 02:34 PM.



#6 OFFLINE   zoomy

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Posted May. 23 2018 - 06:10 PM

I took out the bolt and lubed it well. The bolt moved with slight resistance. The titanium is surface hardened using black nitride. It is a thermal chemical process that infuses nitrogen and carbon into the material.
I’m leaning towards a bad installation of the gas rings. I ordered a JP Enterprises bolt with the one piece gas ring.
.


#7 OFFLINE   gshayd

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Posted May. 25 2018 - 12:05 AM

Gas rings and extractor parts can break. I have had an extractor fail on an AR15 without completing 30 shots. Ordered a new spring with an o ring and it was working great. One test I use: remove the complete carrier from the rifle. With the bolt in its forward position, stand the carrier up on a hard surface. If it collapses under its own weight, the gas rings are probably shot. I also take the bolt in the closed position in my hand and snap it forward. The bolt should come out.

 




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#8 OFFLINE   Rampy

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Posted May. 25 2018 - 12:21 AM

I've got a original AMT hardballer in the safe, has thousands of rounds thru it...and no galling.....

 

 

Sorry, but nope.

In fact, metals need to be sufficiently dissimilar to resist galling. And titanium is more than enough tougher and different from tool steel to work together just fine.

Don't believe me? Just try to cut a piece of titanium with a file (hardened tool steel) and see what happens.

 

As an example, I offer the history of the original AMT Hardballer. The first ones used the same stainless alloy for the slides as the frame, and they had terrible galling issues.

 

The required difference doesn't have to equate to much, as long as one is harder than the other.




#9 OFFLINE   gshayd

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Posted May. 25 2018 - 12:42 AM

Lubriplate's 130-A Mil Spec Grease might have helped that




#10 OFFLINE   Longhair

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Posted May. 25 2018 - 12:54 AM

Rampy, on 25 May 2018 - 01:21 AM, said:

I've got a original AMT hardballer in the safe, has thousands of rounds thru it...and no galling.....

Not a low serial numbered one. The first ones were recalled because of the issue. A minor alloy change and they were fine.

I was a LGS at the time, and a friend and employee of mine bought one that had to go back.




#11 OFFLINE   zoomy

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Posted May. 25 2018 - 01:28 PM

Lubriplate's 130-A Mil Spec Grease might have helped that[/size]


I used the T25 grease.


#12 OFFLINE   gshayd

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Posted May. 29 2018 - 01:21 AM

That's good too. I use the Lubriplate on my M1 garand




#13 OFFLINE   Winkel

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Posted May. 31 2018 - 09:50 PM

I bought a BCG from Midway for my last build.  Admittedly, it wasn't the best quality.  It absolutely ate the first set of rings I had in it.  The second set is holding up fine.  I can only guess the chrome lining in the bolt carrier was rough and finally wore in.







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