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Thread: Measuring Cartridge Pressure

  1. #21
    Boolit Master
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    Another retired engineer type here. I use Quickload (QL) quite a bit. I have checked it against published load data a lot.

    The tool can be very good for most applications if the user knows what he is doing. The biggest exception for QL accuracy is probably revolvers. QL does not even try to address cylinder throat length and cylinder gap. The next item is that QL will never be able to do is predict "spikes" from non-uniform ignition/burn. I also do not trust QL with high powder compression and there is at least one powder (Lil Gun) that just does not seem to perform as modelled.

    Excluding the above, if you do real good at the inputs, my bet is that you get better results with QL than with using published data that is not quite exact for your load.

    The most significant "avoidable errors" will usually be related to percent fill. Case capacity, case length, bullet length and COAL are the raw inputs to get this one parameter. If you get percent fill very close to either QL or to the as tested configuration for published load data you get rid of a lot of potential error.

    The remaining factors are things like chamber dimensions (loose vs tight, gas leakage around the bullet before engraving, and distance for bullet movement before engraving), bullet resistance as it engraves in the rifling, primer affects, and powder burn rate variations.

    With QL, you can "benchmark" your load by measuring velocity, adjusting it to muzzle velocity, and then going back in and adjusting the QL value for powder burn rate (Ba). This will tend to do a "one size fits all" correction for any inputs that were not quite right.

    With good inputs and a good benchmark, the QL estimate of pressure for most loads will probably have an error that is in the same ball park as the error with something like what Larry uses. I say this not because the QL predictions will be that "great". I say it because of the accuracy limitations with the available measuring system for something as messy as chamber pressure.
    Last edited by P Flados; 05-17-2023 at 12:17 AM.

  2. #22
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    Quote Originally Posted by P Flados View Post
    Another retired engineer type here. I use Quickload (QL) quite a bit. I have checked it against published load data a lot.

    The tool can be very good for most applications if the user knows what he is doing. The biggest exception for QL accuracy is probably revolvers. QL does not even try to address cylinder throat length and cylinder gap. The next item is that QL will never be able to do is predict "spikes" from non-uniform ignition/burn. I also do not trust QL with high powder compression and there is at least one powder (Lil Gun) that just does not seem to perform as modelled.

    Excluding the above, if you do real good at the inputs, my bet is that you get better results with QL than with using published data that is not quite exact for your load.

    The most significant "avoidable errors" will usually be related to percent fill. Case capacity, case length, bullet length and COAL are the raw inputs to get this one parameter. If you get percent fill very close to either QL or to the as tested configuration for published load data you get rid of a lot of potential error.

    The remaining factors are things like chamber dimensions (loose vs tight, gas leakage around the bullet before engraving, and distance for bullet movement before engraving), bullet resistance as it engraves in the rifling, primer affects, and powder burn rate variations.

    With QL, you can "benchmark" your load by measuring velocity, adjusting it to muzzle velocity, and then going back in and adjusting the QL value for powder burn rate (Ba). This will tend to do a "one size fits all" correction for any inputs that were not quite right.

    With good inputs and a good benchmark, the QL estimate of pressure for most loads will probably have an error that is in the same ball park as the error with something like what Larry uses. I say this not because the QL predictions will be that "great". I say it because of the accuracy limitations with the available measuring system for something as messy as chamber pressure.
    I have to agree with you. Many people don't know all the data that can be inputed in Quickload like case water capacity, bore dimensions even groove measurements, in addition to fired case and sized case (especially for water capacity). It comes very close for not actually measuing the actually fired pressure and chronographed velocity.

  3. #23
    Boolit Master
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    You Cats enjoy yer Theory, and Computer models...Meanwhile...I remain Blissfully Ignorant...and Shoot Alot..
    Aint blowed Mesef up since the '70's... I believe I will be Just Fine!!!!

  4. #24
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    Quote Originally Posted by racepres View Post
    You Cats enjoy yer Theory, and Computer models...Meanwhile...I remain Blissfully Ignorant...and Shoot Alot..
    Aint blowed Mesef up since the '70's... I believe I will be Just Fine!!!!
    Seems we all managed to do that....not blow ourselves up. However, the ability to measure pressures or to closely questimate pressures gives us another tool to save components and to continue to not blow ourselves up.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  5. #25
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    Quote Originally Posted by Larry Gibson View Post
    Seems we all managed to do that....not blow ourselves up. However, the ability to measure pressures or to closely questimate pressures gives us another tool to save components and to continue to not blow ourselves up.
    Amen to that!

  6. #26
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    yeah, start low and work your way up but why start way too low.

    Question, does everyone else always start with the manual starting loads? I confess, sometimes I start halfway between starting and max. Sometimes I use the starting load and if it is accurate I don't work up at all. Horses for courses.

    Tim
    Words are weapons sharper than knives - INXS

    The pen is mightier than the sword - Edward Bulwer-Lytton

    The tongue is mightier than the blade - Euripides

  7. #27
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    Quote Originally Posted by dtknowles View Post
    yeah, start low and work your way up but why start way too low.

    Question, does everyone else always start with the manual starting loads? I confess, sometimes I start halfway between starting and max. Sometimes I use the starting load and if it is accurate I don't work up at all. Horses for courses.

    Tim
    Sometimes... especially for Contender or Ruger's

  8. #28
    Boolit Master
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    Quote Originally Posted by dtknowles View Post
    yeah, start low and work your way up but why start way too low.

    Question, does everyone else always start with the manual starting loads? I confess, sometimes I start halfway between starting and max. Sometimes I use the starting load and if it is accurate I don't work up at all. Horses for courses.

    Tim
    I used to to some extent, but was also likely to start mid range with a "high margin" gun.

    Most of my workups in recent years have been for loads where I did not have exact matches for the bullet and/or did not have load data with a published "starting load". Many of these loads were also never intended to be worked up to max SAAMI pressure. Frequently I have used Quickload and started my workup at a predicted pressure at the low end of the range I wanted to be in.

  9. #29
    Boolit Master
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    I start low when loading boolits for which there is no load data. If I have the exact bullet shown in the manual, I usually start in the middle. Bullet design can have a surprising affect on pressure, due to factors in addition to weight and net case capacity. I’m starting to suspect multiple lube grooves can drive up pressures.
    I could be wrong - it happens at least daily.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check