Page 2 of 2 FirstFirst 12
Results 11 to 18 of 18

Thread: POF E2 extraction chamber technology?

  1. #11
    Join Date
    Jan 2010
    Location
    Depends on the day
    Posts
    82
    Feedback Score
    0
    Quote Originally Posted by Eric D. View Post
    How does a lubed cartridge increase chamber pressure? A lubed cartridge will increase the force (shear stress) on the bolt lugs because of reduced friction between the chamber wall and casing but I don't see how it will increase chamber pressure.
    Not an expert here but I'm assuming it's because liquid does not compress and the lube on the casing prevents it from expanding.

  2. #12
    Join Date
    Oct 2010
    Posts
    962
    Feedback Score
    21 (100%)
    If we're talking boundary layer film thickness I'm a little skeptical.

    Now, I'm not tracking here. It sounds like a rehash of the same statement - "the effect that lubing cases has on bolt thrust is minuscule compared to the increased thrust due to lack of friction between the case and chamber wall" is how I'm reading it. One causes the other.

    Quote Originally Posted by patrick sweeney View Post
    However, as a variable effecting bolt lug stress, it would be miniscule compared to the increased thrust due to lack of case adhesion to the chamber wall.
    Last edited by Eric D.; 04-14-14 at 18:03.
    B.A.S. Mechanical Engineering Technology

  3. #13
    Join Date
    Sep 2010
    Location
    OR
    Posts
    202
    Feedback Score
    0
    Quote Originally Posted by patrick sweeney View Post
    Theoretically, the film of lube would decrease case expansion, and thus make the combustion chamber just a bit smaller.

    However, as a variable effecting bolt lug stress, it would be miniscule compared to the increased thrust due to lack of case adhesion to the chamber wall.
    Patrick has it right. However, case adhesion to the chamber wall is a highly variable factor and no competent gun designer would use that to determine bolt lug strength. Instead, they simply make the lugs much stronger than necessary. They know that lube will get on ammo and in the chamber. For instance, how many of you use a strong degreaser such as lighter fluid to give the chamber a final cleaning? The first round is almost always from a lubed chamber if the barrel has just been cleaned. The current "best way" to lube the carbine is to be very generous with the oil. Some of this gets on the ammo, especially if the gun is just lubed for a considerable time and not cleaned. Have you seen pictures of carbines lubed and not cleaned for thousands of rounds? They are an oily mess inside! Some of that gets on the brass.

    As Melvin Johnson, the designer of the WW 2 Johnson Automatic weapons, stated, the extractor is greatly helped by lubing the cases and when the ammo is lubed "almost any old hook will do.". Ideally, your weapon should run well without lubing the ammo, and then for added reliability when it really matters put a very light coat of grease or wax on the case. In other words, lube your duty ammo.
    Dave

    INNOVATION IS SELDOM ACCOMPLISHED WITHOUT CONTROVERSY.
    My first rule of a gunfight, thanks to John Farnam's wise advice. "Get away from there!"

  4. #14
    Join Date
    Oct 2010
    Posts
    962
    Feedback Score
    21 (100%)
    Yes, typical practice in engineering. It would be interesting to know what kind of safety factor AR bolts are designed with. I agree that good design would take into account the possibility of lube coming into contact with the ammo or chamber.

    If adhesion is a different phenomenon than friction, though, how is it measured or quantified? What are the units?

    Quote Originally Posted by spdldr View Post
    Instead, they simply make the lugs much stronger than necessary.
    B.A.S. Mechanical Engineering Technology

  5. #15
    Join Date
    Sep 2010
    Location
    OR
    Posts
    202
    Feedback Score
    0
    Eric,

    In addition to friction, there is the strength factor. Brass varies in thickness and can stretch accordingly. As an extreme example, a case that has been reloaded several times may have a ring of weakness in the body. The head may be ready to separate from the forward portion at any time. If it does that, there is almost no "friction" whatsoever. The designer of the weapon must design the locking system as if there was no case at all and still provide a large safety margin.

    "Never put lube on the ammo" is just one of the conventional wisdoms found in the world of firearms. Conventional wisdoms are very often completely false.
    Dave

    INNOVATION IS SELDOM ACCOMPLISHED WITHOUT CONTROVERSY.
    My first rule of a gunfight, thanks to John Farnam's wise advice. "Get away from there!"

  6. #16
    Join Date
    Nov 2008
    Posts
    212
    Feedback Score
    0
    Agreed, any competent firearms designer will design a bolt to have double-safe strength. That is, bolt thrust safety margin to deal with all the potential "no case friction" situations." And then a margin on top of that, simply as good engineering practice.

    You want to keep lube off the case for more reasons than increased bolt thrust, such as lube attracting grit and other smut, cooked lube building up in the chamber to confound proper feeding and locking.

    The operating envelope of the AR is narrow in many parameters. This is one of them; too little case adhesion/friction, and you increase bolt thrust, and accelerate wear. Too much, and you have extractors slipping off rims, tearing through them, or breaking.

  7. #17
    Join Date
    Nov 2007
    Location
    New Mexico
    Posts
    2,958
    Feedback Score
    1 (100%)
    Where we at with this? Anyone tried an E2 barrel? The idea makes sense and I doubt the four small flutes are enough to do anything to bolt life.

    As an aside I believe the HK417 uses a fluted chamber.

    Sent from my SM-G930P using Tapatalk
    Last edited by Tokarev; 11-07-19 at 14:57.
    “The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter cannot be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles."

  8. #18
    Join Date
    Oct 2012
    Posts
    4,013
    Feedback Score
    10 (92%)
    Here is my dumb question for all of the bright people here.. Wouldn't the pressure applied to the case shoulder through the grooves be the same as everywhere else inside the case/barrel behind the projectile? What does pushing on the shoulder do that pushing on the inside base of the case isn't already doing?? I guess the grooves could equalize the pressure between the outside of the case neck and chamber to allow the brass to rebound away from the chamber neck before the extraction process begins.

Page 2 of 2 FirstFirst 12

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •