Truing Quickload Data

Discussion in 'Reloading Forum (All Calibers)' started by Sheldon N, Jan 20, 2016.

  1. Sheldon N

    Sheldon N Silver $$ Contributor

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    Quick question for those of you who use Quickload. I'm testing out a couple different 155g bullets (Scenar, Sierra Palma 2156) in .308 caliber, using the same powder (H4895). Did some preliminary testing with both bullets and got some chrono data, now am truing up the data in Quickload for purposes of additional load development.

    I've measured and input all the correct cartridge and bullet data factors available to me, then used the burn rate (Ba) to true up the velocities to match chrono data. However, I get different burn rates for each cartridge even though I used the same powder (same can) for both. Burn rates are .553 vs .5843, so a decent difference.

    Is this one of those things you just live with, and chalk it up to how each bullet performs in the gun? Or are there additional steps that I might consider to further fine tune my QL predictions?
     
  2. savagedasher

    savagedasher Gold $$ Contributor

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    Before you change anything check the H2O capacity in your cases . Larry
     
  3. gstaylorg

    gstaylorg Silver $$ Contributor

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    Burn rate changes as a function of pressure; increasing pressure is associated with more efficient powder burn. As Larry mentioned, if case volumes are different, it will have an effect on pressure and therefore affect Ba. In addition, even though the weights of the bullets you're using are comparable, the length of their bearing surfaces likely are not. Bearing surface length can affect pressure significantly, so it's not surprising the Ba might change also. A variety of other factors can affect pressure such as temperature, neck tension, etc., and thus may also create a need to re-adjust Ba if they are changed.

    I typically "calibrate" QL to match predicted/actual velocity at a charge weight that is reduced by about 2% from where I estimate the final charge will likely end up. When I test charge weights that cover the slightly higher [estimated] optimal range, it is sometimes necessary to slightly re-adjust the Ba for each increasing charge weight so that predicted/actual velocity match. This is likely because pressure increases as the charge weight increases, therefore the powder burn efficiency and Ba also increase.

    I wouldn't be too concerned about it, your actual testing will tell you where the load needs to be, not the QL prediction. QL is most useful for facilitating load development and characterization of your "final" load, but your actual test results provide the definitive answer of what worked best. Simply adjust the Ba as needed so that predicted/actual velocities match.
     
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  4. Sheldon N

    Sheldon N Silver $$ Contributor

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    Yes, case capacities are measured and equivalent, all brass prep was identical too.

    The whole purpose of the test was to grab some quick chrono data on preliminary rounds so that I could build an OCW load development test around where my predicted OBT node would be. Both cartridges were loaded as you noted, about 2% down from the predicted node so I could true up QL. Each bullet type was loaded to a specific weight based on the dimensions with the bullets being seated off the lands, with roughly similar predicted barrel times and pressures. Now that I have the resulting chrono info I'll be able to use QL to adjust the load slightly to get an OCW with charges weights on both sides of the node. So on that front I don't have any problems, I'll still be able to put rounds on the test target and get all the results I need from both bullets.

    I guess where I was surprised was seeing the divergence in burn rate required to true each load. I had assumed that I would see a pretty similar burn rate since I was using a similar weight bullet and the exact same powder in the same conditions, loaded to similar predicted pressures. I had also suspected that the longer bearing surface of the Scenar was the reason it produced a slower chrono reading than the Sierra Palma, which then requires that the Sierra use a higher burn rate to true up QL.

    It seems a bit strange to use the powder burn rate to correct the data in QL, when the actual issue is physical drag of the bearing surface of the bullet against the barrel. There's not a field in QL to adjust for that, short of starting to mess with the bullet weight.

    Anyhow, was just curious if there was some approach in using QL effectively that I was missing.
     
  5. savagedasher

    savagedasher Gold $$ Contributor

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    What bullet ,primer and powder along with seating. I have found if you're not jumping at least .020 pressure changes. What are you doing? Larry
     
  6. savagedasher

    savagedasher Gold $$ Contributor

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    Barrel length also makes a difference in bullet speed Larry
     
  7. gstaylorg

    gstaylorg Silver $$ Contributor

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    I meant to look last night to find out whether the bullet files in QL take into account the bearing surface length but I forgot to do it...I would have to think that it does. In any event, I've never worried to much about changing the Ba. If the load's velocity/pressure changes, I change the Ba so that predicted/actual velocity match and go from there.
     
  8. Sheldon N

    Sheldon N Silver $$ Contributor

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    I've gone through Quickload and I think it only looks at the back half of the bullet. You can adjust the overall bullet length, and the details of the boat tail dimensions (which would affect internal case capacity) but QL doesn't appear to look at the nose length or length of bearing surface or their interactions with the barrel.

    Chris Long's whitepaper on truing Quickload for OBT does indicate that one option is to "fudge the bullet weight value" when adjusting burn rate is not enough. Just wasn't sure where that hypothetical line in the sand was, or what others were doing. Here's his whitepaper on the subject, it also has some commentary on case volume measurement.

    http://www.the-long-family.com/Tuning QL to achieve best results.pdf
     
  9. BikeEffects

    BikeEffects

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    Is Chris Long still an active member of this board?
     
  10. techshooter

    techshooter

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    I don't post much, but I do read the posts when I have time to spare.
     
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  11. stillbear

    stillbear

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    When using coronagraph reading for tweaking Quick load how close do you put the screen to the muzzle?
     

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