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Velocity variance in factory ammo?

Discussion in 'Shooting Related Threads' started by Zoom.Golly, Jul 22, 2013.

  1. Zoom.Golly

    Zoom.Golly Well-Known Member

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    I think Neil had a post on this, but darn if I can find it. So......

    In a box of 25 factory shells, what is the typical extreme variance in velocity?

    If it makes a difference, let's assume AA, STS, Gold Metal quality ammo.
     
  2. zzt

    zzt Well-Known Member

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    Sam, for STS 10z, light 8s and Nitro27 shells, the ES averages 25pfs and the SD comes in between 9 and 10. I do recall seeing data posted by Neil and others suggesting some other brands of supposedly premium ammo are not as good.
     
  3. JT 27

    JT 27 Member

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    As memory serves me, the study showed Big Purple to have the lowest standard deviation.
     
  4. Zoom.Golly

    Zoom.Golly Well-Known Member

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    Sarge the question is to find a base-line to compare reloads.
     
  5. Neil Winston

    Neil Winston Well-Known Member

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    Sam, the problem is that how you measure it is probably going to be more important than any of the variables you mention, the especially brand. The name on the box is probably least important, over the long run.

    Average reloads, if chronographed "correctly," are likely to show SD's in the 8 to 12 range. Factory loads are usually at least as good, often better, ranging From a range SD of 4-s to through a common bulge of 6-10's and hardly ever more than that.

    "Chronographed correctly" is really the key here, not brands. For home chronographs that means cylinder-or-close constriction, a distance that works, and lighting that works too.

    Full-choke chronography, with light-operated chronographs, doesn’t mean a thing. Nor do data which requires you to throw out reading which are "all wrong." Two chronos can't be beat if you want the real answer.

    Cylinder chokes, correct lighting (see photos at reference above) and you will find that the factories are, on the average, a often a bit better than you most of the time, but not much. And both are close enough.

    Neil
     
  6. Zoom.Golly

    Zoom.Golly Well-Known Member

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    Thank you Neil.

    Check my memory of Statistics 101. A load with a mean speed of 1200 fps and a SD of 10, will put 68% of its shells between 1190 fps and 1210 fps?
     
  7. Neil Winston

    Neil Winston Well-Known Member

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    Over the long haul probably something vaguely like that, sam, but experience tells me not to think that unless I have data from a _lot_ of shots. Shot-to-shot velocity variability is a moving target and while these ten shots may give an SD of 10, the next may be 5, or 10, or something else.

    I've found that SD's are not very repeatable at all (especially the ultra-low ones) so I just make categories:

    1. Good, under 11

    2. Average: 11 to 16 (Average in the sense of nothing special, not most typical.)

    3. Below average 16+

    Most factory shells will hover in the good ranges, most of the time, while reloads may or may not though they most often do. Over 16 indicates problems which should be tracked down; again assuming you are using a very open choke and are having a good day. Some days things don't work right and you have to test again. It's nice to start a test session with something you know should do well - say factory lights - to be sure the rest of the ammo and day won't be wasted.

    If you want to test with a full choke, don't try to evaluate the consistency of your ammunition, just go for speed.

    Neil
     
  8. Neil Winston

    Neil Winston Well-Known Member

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    Eddie, take note that in section 4 I tested one brand - it was Remington, by the way - of shells from lite to handicap and all had pressures centered around 10,000 psi. I would have found the same from other manufacturers.

    Ed Matunas wrote that while he had covered every shell pressure possible in a career of shotgun writing, looking back he'd have concentrated on the ones around 10,000 psi a lot more because they were the best ones.

    Neil
     
  9. Wass

    Wass Member

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    Neil-

    Sounds like you have some experience with chronographing shotgun loads.

    I own a fairly nice chronograph and use it to test the velocity of my hand loads for my rifles.

    I once tried to chronograph my shotgun hand load, but it didn't work. I couldn't get a reading that made sense. I was short on time and had to give up quickly and haven't tried since.

    Do you have any pointers for how to effectively measure velocity of a shotgun load using a basic chronograph that you can purchase for $200 or so?

    Does the chronograph actually trigger on the shot string, or does it sometimes trigger on the wad instead?

    thanks,

    Wass
     
  10. Avaldes

    Avaldes Well-Known Member

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    Wass, read Neil's website. He goes into great detail about his experiences using light operated chronographs. Like he said here, the results will be directly tied to the quality (and details) of your test setup. That doesn't mean $$, but attention to the details of your test.
     
  11. Bob Butler

    Bob Butler Active Member

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    Neil,
    is the answer to the full choke vs Cylinder information in one of your write ups? I do not remember reading it.
    How much does the full choke effect the reading and is it repeatable across different guns, or specific to a single choke?
    To the OP, if you want to measure your shotgun loads Neil's writing on it is very helpful.
    I learned a lot from it.
    Esp. about making a more effective sky screen and how many to test.
     
  12. shot410ga

    shot410ga Well-Known Member

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    In my test, nitro 27's were the worst, from 1325-1220 fps out of one box. 3 dram AA's were the best +/-10 fps at 1250 fps out of one box. Others I tested over the years were generally around 20+/- fps. Unscientific, but that's what I found.
     
  13. Neil Winston

    Neil Winston Well-Known Member

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    Wass, though your fairly nice chronograph didn't work with shot, I don't think the "quality" of the unit is a reliable predictor of shotshell usefulness. For example, I had a famous-name unit which I couldn't make work at all in spite of two trips back to the factory and a gift from them of several sensors. I gave it to a friend who test his AR reloads and he says it couldn't work any better - it's just great for bullets.

    Light operated chronographs are said to trigger off the leading pellet but that can't be true based on results with full chokes - two units will randomly differ by 30 fps reading the same shot. Better to think that they trigger on "some shot" and conscious design differences - not "quality" - will result in good or bad shot performance.

    I think that variability with full chokes discounts the common theory that the units trigger off the wad. If they did, two in a row would read the (about) same regardless of choke. But they don't - they only read the same with cylinder chokes. So it really has to be the shot - it's the shot's distribution that changes when you choke, not the wad's.

    I think you can't beat Pro-Chrono units and the digital is nice since you can pair an HP printer to it and you really have the ultimate setup, especially if you mount two on a 3-foot rail and shoot over the first, then the second, with every shot. Crony in all versions and Oehler 35p have done well too. But none much better than the cheap and simple Pro-Chrono.

    I think if you read the link above you will get about everything I know and, as far as I know, little has changed in the decade since I wrote it.

    To get useful data you need to use as open a choke as you have. Cylinder and skeet are fine but from there in tighter things just keep getting worse, accuracy-wise, especially when trying to test ammo speed variability where full chokes just fail, there's no other way to say it.

    Neil
     
  14. SteveT

    SteveT Member

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    Some dated information but it is probably still applicable. From a Winchester Western "Product Engineering" report dated April 4, 1979 compairing 20 Gauge - 2 3/4 inch - 2 1/2 PDR. Dram Equiv - No 9 Shot AA Skeet Loads to the competition.
    stevet_2008_030371.jpg

    stevet_2008_030372.jpg
     
  15. Dr.Longshot

    Dr.Longshot Banned Banned

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    There is very little deviation in new shells and my re-loads


    Gary Bryant