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Why does everyone worry about pressure?

Discussion in 'Shooting Related Threads' started by short shucker, Jan 20, 2010.

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  1. short shucker

    short shucker TS Member

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    I've been reloading for 10 years and have learned that as long as the load is below SAMMI spec's then everything is groovy. I've yet to get data from the manufacturer that exceeded SAMMI spec's.

    Every time someone refers to data the first comment is how low the pressure is. Why? It has nothing to do with recoil.

    The only loads that I get concerned about keeping the pressure low on is my 28ga and 410 shells. I can usually get a little more life out of them if I keep the pressure down.

    ss
     
  2. myevh3

    myevh3 TS Member

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    My guess is wear and tear on the gun over the long haul.
     
  3. Unknown1

    Unknown1 Well-Known Member

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    <I>"Every time someone refers to data the first comment is how low the pressure is. Why?"</I>

    The ballistics specialists I know won't load a shotshell that comes in at less than 9500 PSI peak chamber pressure. If the chamber pressure is too low (lower than 9000 PSI for them) the powder burn is incomplete and irregular and consequently the performance of those shells will be inconsistent.

    MK
     
  4. PerazziBigBore

    PerazziBigBore TS Member

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    Higher pressure fatiques metal quicker.. Anything under 10,000 poses no problems in just about any modern shotgun.. Some like to put things to the brink edge.. then complain when something fails.. In thicker barrel.. made of hi grade steel.. Most will outlive us... But those paper thin jobs..especially on some of the older doubles.. Well.. less pressure is a prudent thing.. There is a book out.. "Feeding fine doubles"..I think Ballistic Products sells it.. and it goes into detail..about the how and why a pressure number is so important..
     
  5. wayneo

    wayneo Active Member

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    I don't know where to begin with this one. You have to understand that gunpowder deflagrates.

    Higher pressures always means higher temperature.

    You want a complete burn of the gunpowder with the lowest pressure. (More efficient, less waste). In other words, you want the energy of the expanding gases to preform work on the shot column and not create useless heat dissipating into the barrel.

    This doesn't mean you want low pressure, just the lowest pressure for complete combustion. Its been a long time since my physics class, I'm sure someone can explain it better. Wayne
     
  6. Quack Shot

    Quack Shot Active Member

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    The main reason to select lower pressure loads is VERY simple. There are many variables that can change the pressure of the load that you assemble. If you select a load that develops, say 10,000 PSI, then you would expect to be somewhere in the ball park, right? Add a deeper crimp, a different primer, a sligtly different wad, etc., and your pressures could stack up over the max. Components will even change from lot to lot, so it's best to have a little headroom for error. Temperatures can also have a marked impact on pressure. Load a shell with a load developed at 70 degrees and leave those loads in the car in the summer months. The pressures could easily go over the limits just from temperature alone. Now add to that the fact that Trap/Target shooters shoot a tremendous amount of shells, you have the opportunity for disaster.

    Now I don't know about all the other "Experts" on this forum, but I'm one of the few that do not have my own ballistics lab. I have to outsource any pressure testing and that gets expensive real fast. I do have a few chronographs, but they will not give me an indication of pressure. I therefore, have to rely on published data, or my own test results. I approach published data with some caution and am very conservative when it comes to pressures. I test my loads over a chronograph and look for consistent velocities. That's the best we can do unless we have the facilities and resources to do otherwise.

    Think about the gun surviving a few over pressure loads. Most guns will, with little effect. Then think about feeding it 50,000 of your pet wonder loads for the back fence games. It would have to be pretty strong to take that. I don't wish to tempt fate.
     
  7. phirel

    phirel TS Member

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    Wayne- You did a good job explaining the required pressure for good loads. I would add that reloading manuals publish safe loads. Some of the low pressure loads found in reloading manuals are safe, but not real good.

    Pat Ireland
     
  8. TinMan88

    TinMan88 TS Member

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    Shucker, Isn't it usually the second poster that cautions a person to follow DATA and BE SAFE! The first poster asks the question "how bout this load" (or practice) and calls for comments about pressure. Some folks just need reminding. Lets all do it the right way. Regards, The TinMan


    P.S. You post a cute graghic about fishin. Did you just throw a long cast?
     
  9. short shucker

    short shucker TS Member

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    Here's an example of what I'm talkin' about.

    Remington hull, 21 grains Green Dot, Winchester 209, DRF8 wad, 1 1/8 oz of shot, Yields a 1225 FPS load out of my gun and has a pressure of 9,000psi.

    Remington hull, 18 grains of Titegroup, Winchester 209, DRT12 wad, 1 1/8 oz shot, Yields a 1235 fps load out of my gun and has a pressure of 11,000 psi.

    Both of these shells shoot fine year round. Both are clean burning (very little residue in the barrel). No discenable heating difference between the two shells. The felt recoil is the same to me.

    You tell people the psi on the Titegroup load and they just start getting all weird. They start saying that is too much pressure as they are holding a new Nitro 27 in their hands. Yet they'll load a 1200fps shell with Clays and the pressure is nearly the same.

    ss
     
  10. luvtrapguns

    luvtrapguns Well-Known Member

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    I always used SR 7625 powder. Data from the Lyman Book at the time (mid 70's) showed pressures in the 5000 to 6000 range. According to some of the comments I have seen on TS the shell should not go BANG, but the funny thing is they always fired just fine. I always felt new shells were inferior to my reloads. They were a little dirtier but not a problem with a break open gun. No intention to start another debate but felt recoil seemed less.

    RXP hull, 18.5 gr SR7625, CCI 209, Fed wad (spiral type mid section), 1 1/8oz Magnum 8 1/2 shot.

    For HC: Substitute 20.5 to 22gr and use 7 1/2 or 8 shot.

    Marc
     
  11. birddog1964

    birddog1964 TS Member

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    Tell me if this is right or wrong,


    I can load 2 shells with the same components and add 50lbs more wad pressure and a tighter and deeper crimp and raise the PSI a lot more.

    thanks
    lee
     
  12. Unknown1

    Unknown1 Well-Known Member

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    That's right.

    An increase in the crimp depth of .020" can raise the peak chamber pressure 1000 PSI and more.

    MK
     
  13. Shooting Coach

    Shooting Coach Banned User Banned

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    One reason I stay away from red-line loads is simple. The factory is loading new brass, and I am loading hulls that have been picked up and fired in who knows what kind of gun, that may be in good or poor condition. It could have an over sized chamber that has stretched and weakened the case head.

    I also prefer over 9,000 PSI and less than 10,000 PSI for my reloaded shot shells.
     
  14. dverna

    dverna Active Member

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    Quack Shot has pretty well nailed it. Why push the envelop when we do not need to?

    Engineers understand that a factor of safety is incorporated in any design. A higher safety factor is a good thing.

    Using a high pressure load load in trap does not offer any advantages.

    Don Verna
     
  15. scott calhoun

    scott calhoun Well-Known Member

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    You guys are going about it from the wrong direction.

    I recently purchased one of the first new guns available from the Kuhner Gun Manufacturing company - you remember the one Joe was starting that would build guns that were safe for any load?

    With the new gun I can load a shell to any pressure that I want (still observing the ATA rules on velocity and charge weight). In addition, since there is nothing in the rulebook that I can find that specifically prohibits it, I'm able to drop a 20 gauge shell in the tube first so that I'm really shooting over 2 ounces of shot at each target. Ammo cost for each event is double, but you should see how hot the core of my patterns are.

    Scott
     
  16. TinMan88

    TinMan88 TS Member

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    Does everyone weigh the SHOT DROPS? Small booboo here and your metre is off the meter. Tight crimp. Summer day heat? And look at the poster elsewhere that followed max data and later edition powder book redlined it. No wiggle room. 4 thousand shells to cut apart. OUCH!

    It might not be recoil that makes ya flinch!
     
  17. Quack Shot

    Quack Shot Active Member

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    TinMan88

    Yes, I actually weigh the shot drops as well as the powder drops. There are some differences in Shot that can cause a slight variation in the shot payload's weight. Harder shot usually comes out a little light, so some modification or adjustment might be needed to get an exact amount as desired.

    I don't temp fate when loading ANY ammunition. I'd rather have a little less velocity and know that my loads are safe enough to shoot in Quantity.

    My comfort range for the 12 ga target loads would be between 7500/8000 and 9500 PSI or so. I try to stay well under 10,000 for a little margin of safety. If I need more velocity, I use a different powder and keep the pressures reasonable.
     
  18. phirel

    phirel TS Member

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    Apparently many shooters are concerned about pressure but I believe very few have tested the pressure of their loads.

    A reloading manual will state that a certain size bushing will drop a given powder charge, but all of us know that is only an approximation and the powder charges must be checked with a scale. But then many will turn a few pages in the manual and read that a certain load will generate 9,000 pounds of pressure and accept this number without question. Has anyone wondered why the published pressures always seem to be in nice round numbers? Could they simply be reconciled approximations? If a load generates 9,000 pounds of pressure at 70 degrees F, how much does it generate at 85 degrees F? How does a primer or wad from a different lot affect chamber pressure? Not every primer and wad are exactly the same.

    Pat Ireland
     
  19. Andy44

    Andy44 Active Member

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    LURE CHANGE!!!
     
  20. Unknown1

    Unknown1 Well-Known Member

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    I had my pet loads P & V tested using Eagle shot, which is softer and heavier per drop than either Lawrence or West Coast (which I also use). Once I have an acceptable pressure with the heavier shot I have little to worry about when using the same data with the lighter, harder shot.

    MK
     
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