Could someone with a Ruger PC weigh their bolt for me?

Discussion in 'Rifle Country' started by zaitcev, Sep 30, 2019.

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  1. zaitcev

    zaitcev Member

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    I had a case failure in my 9mm AR yesterday. No injuries. Still, I'm thinking about putting a heavier buffer into it, under a suspicion that it extracts while pressure is still too high. I already checked that the case sits deep enough in the chamber, so that's not it.

    But before I go wild with tungsten, I'd like to have hard data, and that's where I need help.

    Could someone with a Ruger PC Cabine put their slide onto a kitchen or postal scale and share the result? Not need to take a photo, I only need the number.

    To start off, currently the weights are: bolt - 13.5 oz, buffer - 5.6 oz, total - 1 lb 3 oz or 540 g.

    Thanks in advance.

    ar9_case_blow_20190929.jpg

    P.S. If folks with Kel-Tec SUB-2000 chime in, it would be welcome too.

    UPDATE: 23.0..23.4 oz for Ruger, or about 657 g. No SUB yet.
     
    Last edited: Oct 2, 2019
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  2. someguy2800

    someguy2800 Member

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    What recoil spring do you have in it?
     
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  3. Elkins45

    Elkins45 Member

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    I had to do the same thing. I ended up pouring a full length rifle buffer full of lead.

    This is one of the reasons I hold the 9mm AR in such low regard.
     
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  4. Rule3

    Rule3 Member

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    I din;t know a Ruger PC was an AR??

    I have a Ruger PC 9 but it's in the safe.

    What ammo, factory or reloaded remanufactured??
     
  5. zaitcev

    zaitcev Member

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    I only want to know the mass of the reciprocating part, which is the bolt in the Ruger. Since the operating system is identical, this is hard data that I need in order to determine the target mass for the AR. I am assuming here that Ruger designed their gun correctly and the mass of their bolt is sufficient.
     
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  6. zaitcev

    zaitcev Member

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    It may seem less than obvious to many, but the spring rate does not matter in this instance. The force exerted by the gas on the bottom of the case, also known as "bolt thrust", exceeds the force exerted by the spring by 2 orders of magnitude. So, the distance traveled by the bolt before the bullet leaves the barrel is only determined by the bolt mass. You can install a spring that is 10 times stronger (!) and it will change basically nothing, as far as possible case rupture is concerned (2% difference of back-out distance or thereabout).
     
  7. someguy2800

    someguy2800 Member

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    I can only tell you I got bulged cases in mine running a normal carbine spring and never got another again after putting in a +10% AR10 spring and a spacer
     
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  8. Rule3

    Rule3 Member

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    I do not know what rifle you are talking about a Ruger PC 9 Carbine is not an AR platform.??

    https://ruger.com/products/pcCarbine/models.html
     
  9. saiga308

    saiga308 Member

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    trucker long hauling everywhere LOL
    primmer looks round so it wasnt a hot charge'o_O out of battery for sure
    download.png
     
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  10. saiga308

    saiga308 Member

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    trucker long hauling everywhere LOL
    sig mag being used found this
     
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  11. saiga308

    saiga308 Member

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    trucker long hauling everywhere LOL
  12. briansmithwins

    briansmithwins Member

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    I’d agree with OOB instead of the bolt opening too fast.

    I also agree that spring weight has almost no affect on opening time. A stronger spring might ensure the bolt is actually closed before firing, which is important too.

    Lots of well designed 9mmP carbines have safeties that prevent OOB case ruptures. I haven’t seen a 9mmP AR that had such a feature.

    BSW
     
  13. Gtscotty

    Gtscotty Member

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    I understand what you're after:

    IMG_20190930_200431942~01.jpg

    I'd say 23 - 23.4 oz for the bolt and the portions of the recoil spring assembly that move with the bolt.
     
  14. sequins

    sequins Member

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    Thanks for actually posting the data. Who cares if it's not an ar...
     
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  15. zaitcev

    zaitcev Member

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    Thanks a lot for the data. So, for 13.5 oz bolt in my case, buffer ought to be about 9.5 oz in order to achieve similar parameters.

    Honestly, I'm thinking about OOB too. But I can't see why. The bolt is not too short, so it is under tension through the buffer when in battery. This is not full-auto where it can bounce out.

    I'm going to look into something like Sprinco's buffer spring that QuarterCircle10 sell. Some people also suggested using an AR-10 spring instead.

    In addition, is there a better firing pin return spring out there?
     
    Last edited: Oct 1, 2019
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  16. mgmorden

    mgmorden Member

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    That's not an AR bolt.

    I kid, I kid :).

    Just be aware if your gun is setup for last round hold open - 9mm AR's have a habit of breaking bolt stops. The heavier bolt/buffer combo when it slams back forward puts a lot of stress on it. Some people stack quarters behind the recoil spring to lessen the travel distance, but either way, a heavier bolt/buffer impacting the bolt stop coming forward will exacerbate the issue.
     
  17. zaitcev

    zaitcev Member

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    Or, they could use this:
    https://www.joeboboutfitters.com/New-Frontier-Armory-9MM-40S-W-Buffer-Spacer-p/nfa-9mmbufferspacer.htm
    Or, a longer buffer.
    Quarters are good to measure how much you exactly need, given your specific buffer tube and buffer. And then you dump the quarters out and insert a wooden dovel of the same size. Or, print a spacer on a 3D printer.
     
  18. someguy2800

    someguy2800 Member

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    I have the NFA spacer as well as the above mentioned +10% AR10 spring in mine. It really calms down the jump and recoil from the buffer slamming into the back of the buffer tube. Much nicer to shoot. I bought the NFA one rather than making a spacer because I assumed the NFA spacer was some type of rubber or urethane to absorb some of the bolt carrier energy, but its not, just a hard plastic.
     
  19. Elkins45

    Elkins45 Member

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    The best spacer IMO comes from the hardware store. Remember the rubber stoppers that went into flasks from high school chemistry class? You can get them in the miscellaneous drawers where the specialty fasteners are stored. Drop one between the coils of your recoil spring and it actually does disperse a little bit of the recoil of a heavy bolt. If you get the right size it jams into place and doesn’t need to be secured.

    I turned a spacer out of a nylon rod but I think I like the rubber stopper better.
     
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  20. ponchh

    ponchh Member

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    I've seen brass do that before. Just for fun, do a plunk test. And don't ask me how I know.
     
  21. Elkins45

    Elkins45 Member

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    This is what my brass looked like before I made my heavy buffer. Not every round, but a good percentage.

    [​IMG]
     
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  22. zaitcev

    zaitcev Member

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    It passes the plunk test fine. That really is the mystery of these OOB issues.

    I am going to collect brass and see what it looks like. I forgot to examine it for bulging.

    With that out of the way, I have a DPMS red 308 spring on order, as well as an 8 oz buffer. We then can compare the brass and see if anything changes.
     
  23. Demi-human
    • Contributing Member

    Demi-human maybe likes firearms a little bit…

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    Everytime a Nine AR starts to make sense to me, one of these threads gets posted...:what:

    Keep me updated, @zaitcev.
     
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  24. zaitcev

    zaitcev Member

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    It really is a question of money. Until I put the extra spring on order, I spent $390 on this gun. But someone else can buy a CMMG Resolute nee Guard, which uses exactly the same OOB safety as AR-15 in .223, because it features a normal bolt and its carrier. It's a great little system, if you have $1,300 for the peace of mind.
     
  25. Varminterror

    Varminterror Member

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    I absolutely love seeing photos like these. I’ve had a couple OOB’s and one over pressure event (several blow outs with an old 10/17HMR), been at matches with a few others, but have never captured my own muffin-top case.

    These always astound me - getting SO CLOSE to falling off of the cliff without actually falling is almost an art form. A guy would fail many times even TRYING to accomplish this, so accidentally stumbling upon the conditions to produce it is truly amazing to me.
     
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