1. Attention: We have put together a thread with tips and a tutorial video to help with using the new software. Please take a moment to check out the thread here: Trapshooters.com Tutorial & Help Video.
    Dismiss Notice

Auto function - how much pressure needed ?

Discussion in 'Shooting Related Threads' started by amboy49, Feb 6, 2011.

Thread Status:
Not open for further replies.
  1. amboy49

    amboy49 Well-Known Member

    Joined:
    Jul 23, 2007
    Messages:
    1,161
    Location:
    out in left field
    Shot some targets today in Indiana - temp was about 30 degrees. Shooting reloads with 1 oz of shot in my Beretta 391. The loads are designed to be light ( I hate recoil ) but the shells didn't have much ejection " umph !" Is there a minimum shell pressure I should be striving for to get reliable shell ejection ? If so, I can recheck my reloading data. If not, I'll keep shooting the "light" loads.

    Thanks.
     
  2. Pull & Mark

    Pull & Mark Well-Known Member

    Joined:
    Mar 9, 2006
    Messages:
    5,419
    amboy49, I'm not a autoloader shooter or have vast knowlegde of these guns per say, but I'm pretty sure that Berreta has different gas check valves for your gun that are made for light, normal, and heavy loads. You might try using one made for light loads and also see which one is in your gun right now. This should solve your problem and let you keep shooting your nice light loads. You may or may not have to replace a spring or two as well. Good Luck and Break-em all. Jeff
     
  3. mrskeet410

    mrskeet410 TS Member

    Joined:
    Jan 29, 1998
    Messages:
    3,064
    For gas operated autos it's not the pressure that works them, but the gas. Some powders, e.g. PB and International Clays, produce a lot of gas with low pressure, and consequently work autos very well. Other powders such as Red Dot produce less gas at higher pressures. But if you are using load that isn't working your auto, add more powder as long as its a published load.
     
  4. pyrdek

    pyrdek Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,296
    A while back I read an article about gas operated semi-automatics. It had some graphs of pressure curves and the function results.

    What I came away with from the article was that it was NOT the peak pressure (what is normally listed in reloading manuals) but the time/pressure curve. A higher pressure peak that only lasted an instant did not function as well as a lower pressure that was sustained for a longer period of time. The longer time/pressure curve load gave a gentler but more sustained push to the action. It is kind of similar to a quick sharp jab punch to the arm versus a longer push kind of punch. Think which one moves your arm more. The same holds true to your shotgun's action.

    Some very fast burning loads would generate their peak pressure and already be dropping before the wad got to the gas ports while other loads would generate their peak pressures when the wad had cleared the ports and thus allowed more gas to get in to work the action. This problem was especially true with lighter loads of shot and very fast burning powder.
     
  5. mrskeet410

    mrskeet410 TS Member

    Joined:
    Jan 29, 1998
    Messages:
    3,064
    Pyrdek - That's the kind of stuff "gunwriters" write about. Only problem with that theory is that peak pressure with fast or slow powders is reached while the wad is still in the hull. What matters is whether a strong gas bubble extends past the gas ports.
     
  6. Shooting Coach

    Shooting Coach Banned User Banned

    Joined:
    Sep 14, 2006
    Messages:
    8,357
    Location:
    Nashville Tn
    The good thing about the Beretta is, with different springs, it can be tuned for the loads you shoot.

    Call Cole's and ask for their "red" spring. It keeps the gas valve closed with lighter loads to better operate the gun. Heavier loads use a lighter spring to open the gas valve to allow excess gas to escape and not damage the action.

    With the red spring, do not shoot "Atomic Annie" loads. A new action spring might be a good idea as well.

    Some powders are so fast that pressures have peaked and are dropping before the wad leaves the hull. Pyrdek is on the money. Breech pressure means little as far as to the level of residual pressure at the ports.
     
  7. pyrdek

    pyrdek Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,296
    Here are a couple of links that lead you to information on pressures in firearms. One very interesting thing occurred when a test barrel was being used on a rifle caliber. The Peak Pressure occurred AFTER the bullet would have left the barrel had it not been for the longer pressure test barrel! The pressures in that case exceeded 81,000 PSI, which approaches the yield strength of the steel of the barrel. This particular test was a rifle, as are most but not all tests shown, so it can only suggest a possibility of something similar happening in a shotgun barrel. It was thought that unburned powder may have deflagration causing the high pressure spike. What is scary is that this was with a factory load! There are shotgun tests results listed which did not exhibit this phenomenon.

    Personally, I do have to wonder if such a thing happened in a shotgun could it explain the, oft quoted here, problems of some shotguns blowing up. That is just a thought and not a definitive statement.

    Wolfe Publishing also has a book out involving pressure factors in firearms. I have not seen this book so I can not comment on just what it says or doesn't say.

    As for mrskeet410 comment, yes, the peak pressure does occur in the shell. My statement was poorly worded. I intended to tell that the higher pressure spike had already dropped well off before the wad cleared the gas ports and not that it had occurred after the ports were cleared while other loads did continue to exhibit a higher sustained pressure AFTER the wad had cleared the ports even though it was not the peak pressure nor necessarily even as high a peak pressure as the shorter duration peak.

    Here are some links you may want to check out.

    RSI Pressure Tests

    Shotgun Pressures

    For the Rifle shooters, here is the link to the Wolfe Pressure Factors book (on CD). <A href="http://www.riflemagazine.com/catalog/detail.cfm?ProductID=823"> Link </A.
     
Thread Status:
Not open for further replies.