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Thread: Extractor Spring Questions....

  1. #31
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    I just realize how damn old this thread is....and I've added nothing new. *Feeling intelligent*
    Last edited by BufordTJustice; 07-17-13 at 22:38.
    "That thing looks about as enjoyable as a bowl of exploding dicks." - Magic_Salad0892

    "The body cannot go where the mind has not already been."

  2. #32
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    Thanks for the additional information.

    Quote Originally Posted by WS6 View Post
    I run in everything from unsuppressed 16" middy to a suppressed 10.5" and it works great. Boringly consistent. Colt designed it to eliminate the need for the O-ring, while correcting all of the geometry flaws of the "5-coil" and other poorly designed springs out there. They compress far beyond what is healthy for a spring, the Colt spring does so only marginally. It's a very small spring, and wire-thickness and geometry play a big role. I remember when RSilvers was modeling all of the springs using software, this one far and away was better than any of the others, except the original M16 spring, which had much less tension than this one. However, it is designed to compliment the mil-spec ejector spring, and won't over-power it.
    Is there a link to this anywhere?

    Quote Originally Posted by BufordTJustice View Post
    I just realize how damn old this thread is....and I've added nothing new. *Feeling intelligent*
    It happens. But at least they can't gig me for not using the search!
    Steve

  3. #33
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    Quote Originally Posted by SteveL View Post
    Thanks for the additional information.



    Is there a link to this anywhere?



    It happens. But at least they can't gig me for not using the search!

    Quote Originally Posted by rsilvers View Post
    Just measure up the spring and put it into spring design software.

    The new Colt spring seems to double the force without having that much more stress. So if I wanted to use an extra-power spring, I would pick the Colt design. I would never use it with an o-ring.

    The HK 416 spring is not extra-power and seems identical to the old Colt spring.

    By the way, I put the USGI rifle-length action spring into spring design software and it claimed it would last for a million cycles. Not sure if that is correct or not. The important thing from that is the action spring is not under-designed and so there is no reason to look for ways to improve it. 17-7 is the best material for it due to corrosion resistance. You could do A228 music wire or certified (not commercial) chrome-silicon if you painted the spring. The software thought either would make it last 10 million cycles.

    By the way, a sure-fire way to know if your action spring is out of spec is to remove your upper and put the lower on a scale. Balance it so it stands by itself. Zero the scale. Push on the center of the buffer buffer until it just starts to move. Replace the spring if you have less than 5.3 lbs of force on the scale. 5.8 is normal. More than 6.3 is out of spec.
    http://m4carbine.net/showpost.php?p=...&postcount=166

    Quote Originally Posted by rsilvers View Post
    You can't identify extractor springs by the number of coils. The drawings do not even specify the number of coils except as a reference which is variable. That means the spring maker tests the spring and adjusts the coils and OAL to achieve the lbs of force that is specified on the drawing. Also, each brand may use its own wire thickness and a different OAL.

    I just measured every extractor spring Brownell's sells. I can say there is some scary stuff there.

    The USGI spring from 1971 had a stress/strain ratio under 50% when compressed to 0.112. Those can last 18,000+ rounds. True, they only have 4 lbs of force at this height, but the o-ring will add in the extractor tension without having to resort to an extra power spring.

    Why is an extra power spring bad? Because more force means more stress. Some of the springs from Brownell's had stress/strain ratios above 80%! If you monkey around with extra power springs, then change them every 1500 rounds.

    The new M4 spring that is Copper colored is pretty interesting. It has exactly double the force of the earlier spring but does not have a huge amount of additional stress. If I were going to run a spring without an o-ring, I would use the new Colt M4 spring.

    Or use an old-style 0.022 wire diameter USGI (people call this the '4 coil') with an o-ring and it should last the life of the bolt (but since it is cheap, might as well change it at 5000 rounds).


    Now here is why I feel Chrome Silicon magazine, action, and extractor springs are BS:

    A magazine with the standard 17-7 stainless spring may be stored fully loaded with 30 rounds indefinitely. Note that Chrome Silicon springs will not resist taking a set better than MIL-STD 17-7 magazine springs. A spring 'takes a set' when it reaches the proportional fatigue limit. The higher the tensile strength, the more it can resist taking a set. Here are the material properties of three premium materials*:

    Chrome Silicon:
    Minimum Tensile Strength: 235-300 psi
    Max Operating Temp: 475F
    Fatigue Properties: Fair

    Music Wire ASTM A228
    Minimum Tensile Strength: 230-399 psi
    Max Operating Temp: 250F
    Fatigue Properties: Excellent

    17-7 PH Stainless
    Minimum Tensile Strength: 235-335 psi
    Max Operating Temp: 650F
    Fatigue Properties: Good

    As you can see, all three materials are about the same with the main difference being temperature, corrosion, resistance, and price. 17-7 costs 2.75 times as much as chrome-silicon ** so it only makes sense to give up the corrosion resistance if the price is much lower and you are not worried about rust.

    The CS spring makers would have to believe they have something new and better and that the military is just behind the times or penny-pinching for not using it. That is not true, as CS is far cheaper than stainless springs. The reason the military has not changed is likely because they have actual engineers who work with facts.


    *
    http://optimumspring.com/technical_reso ... _wire.aspx
    http://optimumspring.com/technical_reso ... _wire.aspx
    http://optimumspring.com/technical_reso ... _wire.aspx
    http://www.docstoc.com/docs/4884305/Typ ... CIFICATION
    **
    Fundamentals of Spring Design from the Spring Manufacture's Institute, page 13, table SM-8
    http://m4carbine.net/showpost.php?p=...&postcount=156
    Last edited by WS6; 07-17-13 at 22:49.

  4. #34
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    Quote Originally Posted by SteveL View Post
    Thanks for the response. I noted a typo in my post above and have corrected it. This is what it now ways.



    I didn't mean to say that I would NOT install the black insert.

    I'll go ahead and put the BCM spring and new black insert in the gun. This has me anxious to try shooting some more Wolf ammo (which I happen to have) and see if reliability is improved with it.

    On a side note you mentioned this is an older version of the spring. Do newer DD rifles come with the longer 5 coil spring now?
    I ordered the MK-18 last September so that is as recent as I can state, and it's a sample size of one. You may want to shoot DD an email to verify, but they do build military grade guns, so I can only assume that the 4 coil spring is standard on their BCGs. My DD LW has a BCM BCG installed (I bought the upper and lower separately and added it myself), as well as two other carbines. When I first joined M4C seven years ago, and purchase my first 6920, it had a silver 4 coil spring with a blue insert. As far as I know, the 4 coil spring is milspec, so I considered it an older version. As far as the origin of the 5 coil spring, I recall reading about it in small arms review magazine back in the day, which had an article on the SOPMOD kit. It stated it was part of a SOPMOD (I can't remember if it was in Block I or II) bolt upgrade kit, along with the black insert and O ring, developed thru Crane as a replacement for the milspec 4 coil spring. I could be wrong since it's been many years since I read it. Hopefully, someone with more in depth knowledge will chime in to verify that claim.
    Last edited by RogerinTPA; 07-17-13 at 23:03. Reason: add info
    For God and the soldier we adore, In time of danger, not before! The danger passed, and all things righted, God is forgotten and the soldier slighted." - Rudyard Kipling

  5. #35
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    Thanks for the info and links. I'll read that thread over the next couple of days.

    Quote Originally Posted by RogerinTPA View Post
    I ordered the MK-18 last September so that is as recent as I can state, and it's a sample size of one. You may want to shoot DD an email to verify, but they do build military grade guns, so I can only assume that the 4 coil spring is standard on their BCGs. My DD LW has a BCM BCG installed (I bought the upper and lower separately and added it myself), as well as two other carbines. When I first joined M4C seven years ago, and purchase my first 6920, it had a silver 4 coil spring with a blue insert. As far as I know, the 4 coil spring is milspec, so I considered it an older version. As far as the origin of the 5 coil spring, I recall reading about it in small arms review magazine back in the day, which had an article on the SOPMOD kit. It stated it was part of a SOPMOD (I can't remember if it was in Block I or II) bolt upgrade kit, along with the black insert and O ring, developed thru Crane as a replacement for the milspec 4 coil spring. I could be wrong since it's been many years since I read it. Hopefully, someone with more in depth knowledge will chime in to verify that claim.
    I appreciate the follow up. Until I asked about it here I had been under the assumption that the newer 5 coil spring must be the current mil-spec. That's why you shouldn't assume.


    Either way I have installed the BCM spring and black insert (no O-ring). I also backordered one of the copper colored colt springs linked to above. I'll run the BCM spring and if/when it gives me trouble I'll throw the Colt in it and go from there. I'm not going to worry too much about it in the mean time though. It's not like we're being bombarded with reports of the BCM springs causing problems.

    Thanks again to everyone who responded.
    Last edited by SteveL; 07-17-13 at 23:14.
    Steve

  6. #36
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    Quote Originally Posted by RogerinTPA View Post
    I ordered the MK-18 last September so that is as recent as I can state, and it's a sample size of one. You may want to shoot DD an email to verify, but they do build military grade guns, so I can only assume that the 4 coil spring is standard on their BCGs. My DD LW has a BCM BCG installed (I bought the upper and lower separately and added it myself), as well as two other carbines. When I first joined M4C seven years ago, and purchase my first 6920, it had a silver 4 coil spring with a blue insert. As far as I know, the 4 coil spring is milspec, so I considered it an older version. As far as the origin of the 5 coil spring, I recall reading about it in small arms review magazine back in the day, which had an article on the SOPMOD kit. It stated it was part of a SOPMOD (I can't remember if it was in Block I or II) bolt upgrade kit, along with the black insert and O ring, developed thru Crane as a replacement for the milspec 4 coil spring. I could be wrong since it's been many years since I read it. Hopefully, someone with more in depth knowledge will chime in to verify that claim.
    Pretty sure that is in the MK18 ndia thingy.

    That was before Colts copper or "gold" spring I believe. DD is a good company but in my experiences their MK18 barrels are very overgassed and their extractor spring is underpowered compared to Colts current spring.

    The 10,000 round thing Andrew did for lucky gunner showed the Colt springs lasted far longer than standard springs which were good for around 5,000.
    Last edited by sinlessorrow; 07-19-13 at 14:00.
    Quote Originally Posted by C4IGrant View Post
    Colt builds War Horses, not show ponies.
    Quote Originally Posted by Iraqgunz View Post
    This is 2012. The world is going to end this December and people are still trying to debate the merits of piece of shit, cost cutting crap AR's. Really?

  7. #37
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    Quote Originally Posted by sinlessorrow View Post
    Pretty sure that is in the MK18 ndia thingy.

    That was before Colts copper or "gold" spring I believe. DD is a good company but in my experiences their MK18 barrels are very overgassed and their extractor spring is underpowered compared to Colts current spring.

    The 10,000 round thing Andrew did for lucky gunner showed the Colt springs lasted far longer than standard springs which were good for around 5,000.
    Springco recently debut'd a new 4-coil spring that is not quite as powerful as their original AR15 extractor spring....I wonder if this is closer in performance to the new Colt copper washed spring?

    Thx for adding that about Andrew's test at LG....I had forgotten that.
    "That thing looks about as enjoyable as a bowl of exploding dicks." - Magic_Salad0892

    "The body cannot go where the mind has not already been."

  8. #38
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    Coffee

    Quote Originally Posted by Iraqgunz View Post
    You guys need to drink more coffee or something.
    One cup coffee + Two shots = Good morning America

  9. #39
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    Quote Originally Posted by Robb Jensen View Post
    I see fairly often, usually it's people beefing up extractors on middys and rifle length guns. Their problems are failure to go into battery sometimes and odd jams.

    My trick to getting the extractor pin is to press the extractor on the edge of the workbench and slide the pin in, it's actually very easy.
    Yes, I've heard about over beefin' the extractor and the bolt having a hard time going into full battery. I've personally never needed to add the O-ring or anything on neither of two BCM 14.5 Middies or BCM 20in Rifle upper but, some others may.

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