Can Someone Check This Math, Please?

Discussion in 'General Reloading' started by Joshua M. Smith, Aug 24, 2010.

  1. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast


    Can someone check this math,please? Before I go plugging it into a spreadsheet? It's a .22LR handload.

    Impact  = 0.517490s
    Shot start = 0.060320s
    T(bullet unadjusted) = 0.45717s
    M = 1133fps (75 deg F)
    D = 150ft
    T(bullet) = T(total) - T(sound)
    T(sound) = 150ft/1133s = 0.13239s
    T(bullet) = 0.45717s - 0.13239s
    T(bullet) = 0.32478s
    V(bullet) = d/T(bullet) = 150ft/0.32478s = 461.85fps(avg)
    43.5fps avg loss with CCI bullet, avg of muzzle velocity and velocity at 150ft
    MV = 505.35fps
    My next purchase was going to be a chronograph, then I got laid off thanks to Indiana deciding folks didn't need as much health care as they'd been getting. 'Nuther subject though.

    Any help?


  2. gandog56

    gandog56 G&G Evangelist

    Numbers make poor Grok's head hurt....:34:

  3. Ninja Piper

    Ninja Piper G&G Evangelist

    Yup. It's math. Good job!

    Sorry, couldn't help myself... Can't help you other than confirm that those are indeed numbers.
    Last edited: Aug 25, 2010
  4. samuel

    samuel G&G Newbie

    You handload rimfires?Well,I guess it can be done. You don't give a bullet weight so your figures can't be checked exact but any bullet in .22rimfire leaving the muzzle at around 1130/1150fps would only lose about 100fps in 50yds/150ft.In fact it would be well over 900fps at 150yds. ,,,sam.
  5. texnmidwest

    texnmidwest Sir Loin of Beef Forum Contributor

    Amazing! Never understood how anyone could do that kind of math with out at least a slide rule!

    I have trouble adding up the bar tab with out a calculator. Guess that's why they won't let me drink there anymore. :09:
  6. samuel

    samuel G&G Newbie

    ^ Well you can bet your sweet bippy I don't get the younger generation to do it!!! ,,,sam.
  7. gandog56

    gandog56 G&G Evangelist

    Thanks Tex, you just reminded me how old I am. I took a class to learn how to use a slide rule because there WERE no calculators yet.:chairshot:
  8. Ninja Piper

    Ninja Piper G&G Evangelist

    Slide rule? I thought they were still using the abacus when you were in school?
  9. gandog56

    gandog56 G&G Evangelist

    Too advanced, all we had was piles of rocks.
  10. Whatcha looking for?

    Josh, my first question is what do you mean a "22LR handload"?
    My second question is, if you don't have a chronograph, how did you generate these numbers?
    My third question is what are you trying to measure or calculate?
  11. samuel

    samuel G&G Newbie

    ^ Now gandog is going to get a headache! ,,,sam.
  12. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast


    I handloaded using a primed case and a bullet. Actually did it several times, working down 5% at a time until I got to the noise level I liked.

    Then the formula is pretty straightforward. I derived the speed of sound from temp and barometric pressure that day, and the rest of it was just timing.

  13. samuel

    samuel G&G Newbie

    Well,I can't say too much as I did similar things when my age was still single didget.I still have all my parts and just some minor shrapnel scars.Please be very careful and wear protective equipment. (I'd rather you quit that experiment) ,,,sam.
  14. gandog56

    gandog56 G&G Evangelist

    gandog will be fine, it's his inner nature alter ego Grok that has the math problems.
  15. Josh, first let me say that you can purchase sub-sonic 22s. Sub-sonic eliminates most of the "crack" of a 22LR. I've not tried pulling a 22LR bullet, adjusting the powder, and reseating the bullet. I suspect accuracy would be less-than-useful because of the variable re-grip of the case on the bullet. I've shot CBs for urban pest control and not had any neighbors aware of the gunfire.

    Now, the math: You apparently have a device for recording sound. I don't understand how or why the "start" is 60 milliseconds past zero. Impact must be the time at which the time-measuring device recorded a bullet impact sound. This would be the time in flight of the bullet PLUS the time for the impact sound to return to the firearm. Knowing the speed of sound and the distance, the return time is calculated at 0.13239 seconds. Subtraction yields the time in flight of the bullet (0.32478 seconds). Divide that into the distance gives an average velocity of 462 fps.

    Your next line introduces a value of 43.5 fps as the velocity loss of a CCI bullet; however, you don't indicate the distance or time over which that loss acts. Thus, to simply add 43.5 fps to the average velocity you calculated, may not be correct. Without knowing the parameters of the 43.5 value, you MV may be a WAG.
  16. DaTeacha

    DaTeacha Things are not what they seem. Forum Contributor

    Okay, let's see if I understand what you're working with here.

    You have some device capable of measuring time down to 1 millionth of a second. That in itself is fairly impressive. Apparently you have an electronic timer connected to the trigger or something so pulling the trigger starts the thing, with the .06.... being the lock time, or the lag between when you first start pressing on the trigger and the striker or hammer succeeds in setting off the round.

    You then subtracted to get a time of flight reported accurate to "only" a hundred thousandth of a second, dropping the last zero for some reason not made clear, but apparently not related to significant digits.

    Next, you took the speed of sound (which you for some reason label as M) -- 1133 fps, divided the 150 foot distance by that velocity and ended up with what the time for the sound of the shot to travel the 150 feet should be - .13239 seconds.

    There is another microphone or something 50 yards out where the bullet strikes and that one measured the time between the start of the trigger pull and the impact, .51...... This one is apparently stopped by the sound of the bullet impact downrange and started by the sound of the shot.

    You then took the time to impact and (presuming it was not based on sound coming back to the firing point as covered by the Pilgrim above) subtracted the time for the sound to get there, leaving you with the net time of flight for your bullet - .32478 seconds.

    From there simple division leads to the average speed of your bullet.

    Whether or not your calculations are correct depends on how you measured things. If the downrange timer starts with the sound of the shot and stops with the sound of bullet impact, it seems you are okay. However, if your stop time is based on measurements of sound as 'heard' by a microphone or other device located at the firing point, you need to do as Pilgrim said and allow time for the sound to go both ways.

    How are your timers started and stopped? Knowing that would help a lot.

    As mentioned above, subsonic ammo is not that costly. It will also be far more reliable than pulling and replacing the bullets in .22 LR ammo. Hollow points will make no difference at the low velocities you are working for. CCI, among others, markets CB caps and you can probably find BB caps somewhere if you look hard enough. The low velocities you are seeking will not generate sufficient recoil to operate most auto loaders, so using shorts shouldn't be a problem.
    Last edited: Aug 27, 2010
  17. samuel

    samuel G&G Newbie

    ^^ Oh my GOD!!! I certainly hope Gandog56 alias Grog is on vacation or possibly went hunting and got lost for weeks!!! If he sees these last posts,,,,,,(what little mind he could muster will be gone) ,,,sam.
  18. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast


    It's measured using a laptop and Audacity, which is an audio analyzer program.

    The idea here is to work something similar into a centerfire, like Cooper's, without the balloon head.

    Meantime, heavy .22 CB caps are a good thing. That's what this particular exercise is about.

  19. DaTeacha

    DaTeacha Things are not what they seem. Forum Contributor

    Okay, those are the tools. Where are the sensors? What event(s) start and stop the timing sequence? It looks like you're doing a neat bit of work, but your lab report needs more details. :)
  20. Why not get a 22 caliber pellet rifle that goes somewhere between 7 and 900 fps? Might save your fingers or other parts of your anatomy. Though I guess once upon a time ago they used to sell kits to load 22 rimfire ammo with. But that was long before I was around, just remember reading about it somewhere, so I guess it is possible you may have one of those, but I doubt it. Would also save Gandogs alter ego a big headache!!
    Last edited: Aug 28, 2010