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Chamber Pressure

Discussion in 'Uncategorized Threads' started by Brino, Aug 15, 2008.

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  1. Brino

    Brino Member

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    Can someone explain how two different powders both produce the same 1200fps but have radically differently chamber pressure 8500psi versus 10,100psi using the same wad. Thanks
     
  2. Shooting Coach

    Shooting Coach Well-Known Member

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    Burn speeds are different. Compare it to kicking a door shut with a bare foot, then a tennis shoe, then a boot. The door slams about the same, but the difference is in the foot. LOL

    Your bare foot might move faster, but will stop faster when it hits the door. The tennis shoe will move a little slower, but have more impact. The boot will move slowly, but have the most impact.

    We are not talking about which one will hurt the most.

    I typically prefer to keep my 12 ga loads over 9,000 and under 10,000 PSI.

    Too little pressure seems to cause inconsistent loads, especially in over bored guns.

    As far as maximum pressure, I am aware the factory loads up to 11,500 psi, but they are using NEW brass. I am loading brass which was fired in a shotgun other than mine, which was run through a resizer, which likely weakens the brass slightly.
     
  3. Brino

    Brino Member

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    Thanks, I'm trying to figure out the ideal handicap load without getting hammered, my neck won't tolerate a pounding.
     
  4. phirel

    phirel TS Member

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    Brino- Chamber pressure is not directly related to recoil. Shooting Coach is correct when he suggested a chamber pressure range of 9-10,000 PSI. Pressure less than 9,000 PSI will result in inconsistent powder burns.

    You can, with reasonable accuracy, compare the recoil of different loads by simply multiplying the shot weight by the velocity. The load with the lowest product will have the lowest recoil.

    You indicated that you might have a physical problem with your neck. If this is true, I very strongly recommend that you look at a Precision Fit stock. Several years ago, a friend had to have his shoulder rebuilt as best that surgical techniques allowed. The surgeon was also a shooter. After the surgery, my friend was told that he could never shoot any gun larger than a 22 rifle and he was placed on permanent disability. My friend got a PFS in a couple of months and found he could easily shoot a 100 bird ATA event. After seeing this, both the surgeon and I got a Precision Fit Stock.

    Pat Ireland
     
  5. Quack Shot

    Quack Shot Active Member

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    Chamber pressure has little to do with recoil energy, although there are some on this forum that will tell you they can tell the difference a thousandth of a second can make on a pressure curve. I can't, and really don't see how someone can. The velocity and total ejecta weight has the most bearing on recoil. Reducing velocity or shot payload or both would be a way to reduce recoil, as would adding weight to your firearm.

    I have some severe C-Spine issues and shoot a mild 1oz or 7/8 oz load most of the time. A decent 1 1/8 oz handicap load might start out with a moderate burning rate powder such as Green Dot. I like this load using a Red Versalite wad from Downrange, 20 grains of Green Dot, Winchester primer, STS or Win AA hull, 1 1/8 oz of premium hard shot. I prefer 8s, since they pattern well in my barrels. This load develops around 1225 fps or so. You can use the Figure 8 or WAA12 wads in that load as well. Just confirm the data on your own. If substituting he primer, you are on your own, since that can change pressures dramatically. You can drop the powder charge a little to reduce velocity and recoil. I have used about 19 grains of Green DOt with success and it dropped the velocity to somewhere around 1170, if my memory serves me.
     
  6. phirel

    phirel TS Member

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    Quack Shot- Good post, but I have to make a minor correction to what you stated. The differences in pressure curves is not 1/1000 of a second. These differences are 1-3/10,000 of a second.

    You and I can not distinguish between 1/1,000 of a second, but as you pointed out, others seem to be able to distinguish between 1/10,000 of a second. I guess you and I are not as sensitive as others.

    Pat Ireland
     
  7. Neil Winston

    Neil Winston Well-Known Member

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    Here are the data on which Pat based his post. Though they are from my lab, Pat has confirmed their accuracy using local sources.

    [​IMG]

    and

    [​IMG]

    These examples counter the hand-drawn and basically imaginary published graphs we've all seen illustrating the "push vs jab" effect of powder burn rate.

    Neil
     
  8. Quack Shot

    Quack Shot Active Member

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    Pat,

    I certainly can't tell the difference a few 1/10,000 of a second makes in a pressure curve and apparently gave a big enough interval to almost cover the entire event. A millisecond is a very long time when related to chamber pressures, and I still doubt it would be discernable by most humans. Now, I wouldn't be saying that we are both insensitive people. Only when it relates to recoil. :) Also, just using a higher rib and comb can help by allowing the neck to remain upright. The PFS is a great option, but they don't make one for my gas pipe (1100), or at least I've never seen one. A heavier gun is not an option since I have some serious issues with strength in the left arm. The 1100 has a target contour barrel and is almost light enough for me to hold up. I've been told to stop shooting, but I guess they just had to tell me to quit something and I don't smoke. Hopefully I can get all of these spine and shoulder issues repaired over the next year or two. Afterwards, I should feel like the Six Million Dollar Man and have all of the bills to prove it!

    Neil,

    As always, a picture or a graph is worth a thousand words. :) I remember looking at some graphs illustrating when gun movement started. If I remember correctly, the gun started moving well after the chamber pressure had peaked and mostly dissipated. Great info.
     
  9. Brino

    Brino Member

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    Thanks to all of you, this has been helpful. I have a precision stock that I may have to go back to if my spine gets worse but for now I'm being stubborn about having a wood stock. I do have less trouble with my ljutic being a heavier gun and I have a very upright head position with a fitted stock. Maybe I could weight down my Perazzi for doubles. Thanks again
     
  10. Brino

    Brino Member

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    Thanks to all of you, this has been helpful. I have a precision stock that I may have to go back to if my spine gets worse but for now I'm being stubborn about having a wood stock. I do have less trouble with my ljutic being a heavier gun and I have a very upright head position with a fitted stock. Maybe I could weight down my Perazzi for doubles. Thanks again
     
  11. rifle guy

    rifle guy TS Member

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    I dont believe that the pattern suffers as much as the consistacy of the burn. It may be noticable maybe not but the shot to shot velocity won,t be consistant. hope this helps.
     
  12. Quack Shot

    Quack Shot Active Member

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    chauncy

    PB is a single base powder and it has been a little hard to ignite in cold weather, in my experience. I had decent results, but not with lower pressure loads. I found loading it at, or over, about 8000 PSI was alright, except at temps lower than about 45°. The patterns should not be adversely affected by lower pressures. It wasn't a very economical powder and most of the IMR series powders are also expensive.

    Brino

    I have also tried adding a little weight to my buttstock. I didn't like the change in balance, but it did have a very slight effect on recoil. It just felt funny to me and didn't handle tha same way it did before. I can't add weight to the barrel or forearm, since that would make the gun too heavy for my left arm. Good luck!
     
  13. phirel

    phirel TS Member

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    rev- Can you explain to me how a 1 1/8 oz load traveling at 1200 ft/sec pushed by 7625 could be softer than the same load pushed by another powder. After I understand what you explain to me I will send an e-mail to I. Newton and point out his mistake. Would you happen to know his e-mail address?

    Pat Ireland
     
  14. trappermike

    trappermike Well-Known Member

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    Pat I think I found the email addy. Try NewtonI@appleorchard.org/falling/apple

    Mike
     
  15. omahasportingsupply

    omahasportingsupply TS Member

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    Love the charts Neil. It seems easier to understand when a pictures demonstrates the words. Omaha
     
  16. Quack Shot

    Quack Shot Active Member

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    chauncy

    I have several chronographs, but the one I use the most was the cheapest. I carry a Chrony F1 in my car and use it quite often. It was about $70 on sale at MidwayUSA.com. I have a few others, but the convenience of a cheap unit to kick around works for me. I use it on a simple tripod and have had good results. Be sure to use the tall diffusers and you should be fine. I put a small piece of plexiglass in the front to keep powder and stuff from getting all over the display. Using an open choke seems to give more consistent and accurate results.
     
  17. phirel

    phirel TS Member

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    rev- You are absolutely correct about felt recoil and acceleration rates. Acceleration rate of the shot is related to chamber pressure, but as illustrated by Neil, the pressure differences and resulting acceleration rate differ between a slow and a fast powder by only 3-4/10,000 of a second.

    Using your example of automobiles, could you distinguish between one car reaching 60 MPH in 45 seconds and another reaching 60 MPH in 45.0003 seconds?

    You may be convinced that one powder feels softer on your shoulder than another. But, you really don't feel anything on your shoulder. Shoulder nerves send signals to your brain and you really feel recoil in your brain. You can trick your brain into perceiving something is less or more painful. Not only can you trick your brain, your brain can also trick you.

    Pat Ireland
     
  18. hmb

    hmb Well-Known Member

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    When it comes to recoil, some powders are good and some powders are bad. When you find one that is good, use it, and after each shot is fired, say, "good powder". Golfers will understand. HMB
     
  19. Bird30

    Bird30 TS Member

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    strate The difference is speed. The nitro's are not going as fast, so as everyone has been saying speed and weight means more or less recoil.

    Dave
     
  20. JerryP

    JerryP Active Member

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    If there is any difference I would suspect vibration, but I'm skeptical too.
     
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