Part 310 is an AR donut

Discussion in 'RDB Bullpup Rifle' started by iamscottasus, Aug 2, 2020.

  1. iamscottasus

    iamscottasus Well-Known Member

    Feb 21, 2014
    Hi group! I hope I can confirm this as universally true, but YMMV.
    I was digging in my AR parts to look at some extractor dounts I had. I don't remember who I got them from so I Googled the part number and they reference to an extractor donut from Primary Arms. I suspected these might fit the RDB firing pin retainer, did the side-by-side, fit, test, and yes, they work perfect.
    In the pictures, the donut with the mold flash is the KT supplied and the clean one is the Primary.
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    20200801_235631.jpg
    ^^100 points to anyone who can identify what's wrong in this picture above^^(no, its not the missing retainer pin)
    20200801_235845.jpg
    20200802_091025.jpg
     
    Last edited: Aug 2, 2020
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  2. dazed

    dazed Active Member

    43
    Jun 9, 2020
    Thanks for starting this post, scottie. I was too embarrassed to start one over a silly o-ring, but I'm glad we had our little exchange on the issue.

    A couple weeks ago, I was cleaning my RDB, and took out the retaining pin and firing pin for a deeper cleaning, and the retaining pin was not seating firmly, coming out with a slight touch, noticed that the o-ring was shedding, and coming apart. Split and fell off.
    Obviously, didn't want to fire it in that shape, called up KT and asked if it was just a standard o-ring I could get at a hardware shop. They didn't really answer that question, but took my address and mailed me a replacement part.

    Thing was, I had a 50th bday range and BBQ trip planned that weekend, really wanted to show off my baby. Went to several hardware shops, nothing that small. Went to a specialty plumber shop, and they had them. (1/8 × 1/16) Bought a dozen for $2.

    Got the KT replacement in after the weekend, and it's absolutely the same size, but seems like maybe a slightly different material? The store bought ones are shiny, the KT replacement is dull. Does it mean anything? Idk. Ran 500 rounds through it, no issues.
     
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  3. iamscottasus

    iamscottasus Well-Known Member

    Feb 21, 2014
    The flash on mine was keeping it from seating properly.
     
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  4. RogueIV

    RogueIV Well-Known Member

    283
    Dec 2, 2018
    Only thing I can think of is oil resistance might not be so good on the ones from the plumber. I assume those were made to deal with water not oil.
     
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  5. whynotthinkwhynot

    whynotthinkwhynot Well-Known Member

    135
    Dec 7, 2018
    Good find both of you! I imagine the same size part can be found in auto parts stores now that we know the size. It would be good to have some laying around JIC.
     
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  6. stephen urban

    stephen urban Member

    3
    Jun 23, 2020
    That is exactly the difference. Gun oil and cleaning compounds will swell and soften the one designed for plumbing.
     
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  7. iamscottasus

    iamscottasus Well-Known Member

    Feb 21, 2014
    That depends. What kind of plumbing?
    O rings that small are often made for valve stem seals and designed to last 20 years. Lets find out what Daze has.
     
    Last edited: Aug 9, 2020
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  8. dazed

    dazed Active Member

    43
    Jun 9, 2020
    I don't know a whole lot about the subject, if I'm honest. But I took that into account, and only used the replacement ring for a weekend. And for shorter runs, I'm confident in them. There was absolutely no wear or peel from the ring when I removed it. And it was definitely tougher than the original that fell off.
    If I can get ahold of more of the ones used by Kel-tec, I'll do a "soak" test, put one of each in CPL for a few weeks.
     
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  9. whynotthinkwhynot

    whynotthinkwhynot Well-Known Member

    135
    Dec 7, 2018
    Place your bets! I personally bet there is not going to be any difference. Why? Manufacturing and marketing. The same product is marketed to a different purchasing group by touting different properties. Sometimes there are even different prices. I have a friend who paid $5 for a box of “Squirrel Repellent” to protect his tomatoes, but it was a $1 box of moth balls.
     
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  10. stephen urban

    stephen urban Member

    3
    Jun 23, 2020
    That was just some creative marketing of a product known to repel rodents.

    Which is not the case with things like o-rings. Ones made for use in water systems are of a different material than those used in applications where they are exposed to oil, fuel and other chemicals.
     
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  11. iamscottasus

    iamscottasus Well-Known Member

    Feb 21, 2014
    Dazed was kind enuf to to send me some of his "plumming" Orings. Thanks.
    Side by side with the AR rings, I can't see any differences. One isn't stiffer or softer than the other. Both black soft rubber.
    Like Whynot says, probably the same item. How much competition is there to produce a better 1/8x 1/16 black rubber O-ring anyway? If one supplier makes a good one, why compete?
     
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  12. RogueIV

    RogueIV Well-Known Member

    283
    Dec 2, 2018
    O-rings are made of a variety of different materials and blends to suit whatever the intended use (and price point) is. I mean it won't really matter for our use as it's rather non critical and it's literally just holding a pin in so the cheapest is probably fine.
     
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