QL v3.6 just arrived and its conflicting info

Discussion in 'Reloading' started by datsjeep, May 29, 2010.

  1. datsjeep

    datsjeep Active Member

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    [​IMG]Ok my quickload v3.6 just arrived and I already played with it enough to make my brain hurt. Actually the program seems simple enough however one thing has me a little confused. I have always been under the impression that seating a bullet closer to the lands or increasing the cartridge length will increase preasure.

    So I start dropping in my load info to see what the program gives me. I already have some retumbo loaded up behind the 150 Bergers so I wanted to check what QL would give me for preasure and velocity. I know what the seating depth is and the OAL so I entered that info as well (2.895).

    After I got all the data I thought I would see what happens to the preasure by reducing the OAL, seating the bullets further into the case and creating a little more jump (2.695)

    To my surprise preasure increased and so did the velocity? HUH? The only thing I changed was to reduce the OAL from 2.895 to 2.695. Presure and velocity went from 56524psi 3079fps to 62591psi 3162fps. What am I missing here?

    I will post screen shots as soon as I figure out how.

    [​IMG]
     
    Last edited: May 29, 2010
  2. jwp475

    jwp475 Well-Known Member

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    By seating the bullet farther into the case by .2" you readuced the case capacity and therefore increased the pressure
     

  3. datsjeep

    datsjeep Active Member

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    OK, it also does it if you are only using 95-99% of case. Is that normal? I am still really confused by this. I have not found a single scenerio where seating the bullet closer to the lands will increase preasures in the QL program
     
  4. Autorotate

    Autorotate Well-Known Member

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    Exactly.

    To further expound.....

    You will need to modify the start pressure setting to account for pressure differences unique to your rifle/throat/bullet combination when changing seating depths. That is not an automatic feature...the user will need to input this.

    A method I've used successfully, is to load a string of rounds at varying charges, at all the same seating depth.

    Record the velocities for the string.

    Then use the case weighing factor/start pressure to "calibrate" QL for your rifle, until you can plug in the lowest charge and see a velocity that matches what you saw for that charge, and then do the same with the high charge.

    When I'm able to input the "low charge" of my string, and the "high charge" of the string, and see that both velocities are close to what the chrono saw....then I feel good about the start pressure/case weighing factor for that powder/bullet/seating depth combination.

    You then should be able to correlate the case weighing factor/start pressure figure to other powders, but not seating depths....if you change the seating depth, you'll need to make a change to start pressure once again.

    This all assuming of course, you can trust your chrono results, and didn't forget to account on the effects of temperature can have with your powder:)

    Reminder/disclaimer....QL is not a substitute for a pressure barrel in a laboratory with a strain guage. One must exercise caution, especially when operating at the upper performance levels IAW published loading data when available.

    Good luck!
     
  5. datsjeep

    datsjeep Active Member

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    That makes sense, you adjust both the wighting factor and the shot start pressure. How do you determine which one to move and how much to move them?
     
  6. Autorotate

    Autorotate Well-Known Member

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    QL sees the Case weighing factor is an "efficiency" factor, specifically a relationship between case capacity and bore diameter.

    .40 is a good place to start for the 338 Edge, and a 300 RUM Improved seemed to work with .36 with most loads/powders.

    I would look at your case and compare it's relationship to one of those as a benchmark, and then adjust to start.

    Lower case weighing factor number, equals less total pressure, but more velocity with a given powder charge/bullet weight.

    Higher case weighing factor number, equals more total pressure, but less velocity....

    Start pressure numbers are just like you'd think....

    Higher start pressure, more total pressure and more velocity for a given scenario.

    Lower start pressure, less pressure and less velocity for a given scenario.
    gun)
     
  7. bigngreen

    bigngreen Well-Known Member

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    I am very interested in acquiring Quick load and was reading your thread when I realized that you have 72.5 gr of Retumbo under a 150 Berger! Not trying to be nosy but that will lock up the bolt on my 270 WSM with 140 Bergers, just wanted to give you a heads up just in case. If you can safely light it in your rifle it should be good for over 3200fps thought.
     
  8. phorwath

    phorwath Well-Known Member

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    When I keep everything the same and increase bullet seating depth away from the lands, I see slower MVs over my chronographs. Consistently. I can't speak to QL as I don't own it.

    What I experience is consistent with the loading instructions that come with the HAT bullets. Load up a maximum load with the bullet a bit off the lands. Then increase seating depth systematically while looking for a sweet spot. You'll never experience an excessive pressure load in this manner, as pressures go down. Therefore MV goes down by increasing the seating depth, with the powder charge kept constant.

    So the hypothetical explanation of decreased case capacity = increased pressure does not result in increased MV in the experience of a number of other Threads I've read, or my own experiences shooting over reliable chronographs. I believe giving the bullet a jump start prior to hitting the lands more than offsets the effect of the reduced case capacity. I'll monitor this Thread and see if one of you can explain this line of reasoning, in light of the repetitive experiences of the tester of the HAT bullets. Every single time. Seat the bullet deeper, MVs decrease. That's why changing seating depths alone can be used as a technique for finding an accuracy node - rather than changing powder charges.

    Now, I'm ready to be corrected...
     
  9. Fitch

    Fitch Well-Known Member

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    That is not only wrong, it is dangerously wrong and could get someone seriously injured or killed. I don't care if it came with bullets or not. It is completely inconsistant with the physics of what is happening in a rifle case when the powder is ignited.

    The only way pressures go down by seating the bullet deeper into the case is if the bullet was touching the lands to begin with. However the strength of the effect depends on several parameters that vary with case/powder/bullet combinations.

    Reducing the case volume while keeping the powder volume and ignition constant increases pressure. This is most obvious on straight walled pistol and rifle cases because the bullet diameter is the same as the case body so there is significant volume reduction for small changes in seating depth, but the effect is the same on all ammunition. Peak pressure can happen before the bullet even leaves the case with fast powders, and happens often with handgun ammo. With the slow powders used with heavy for caliber bullets in rifles, like the 180 Berger/Retumbo combination in my 7mmMAG, peak pressure will happen with the bullet about 3" past the throat.

    The examples of reduced case volume and increased pressure have happened, some times tragically. There are numerous cases on record of semi automatic pistols being blown up, literally coming apart due to over pressure, from bullets being pushed back in the case. One casue of this happening in semi-autos happens when the gun is routinely loaded with the mag full and one in the chamber if the one in the chamber is the same bullet, or one of the two bullets on the top of the magazine, are chambered time after time. What happens sometimes, but not always, is that when it's chambered the bullet gets nudged back into the case a few thou. No biggie. Do it over and over and pretty soon that bullet can be pushed far enough into the case to cause a serious, or even destructive over pressure. It can also happen on the first time if the bullet doesn't have enough tension to hold it in position when the round is chambered. A routine caution to those who routinely CCW a semi-auto is to rotate the round being put in the chamber.

    It also happens with rifle cartridges. However, in rifles, the effect of bullet seating depth is not linear and changes direction with a discontinuity happening when the bullet is very close to or touching the lands.

    Starting with the bullet a significant distance off the lands, say a jump of 0.100", at a safe pressure, keeping the powder charge the same and decreasing jump, will reduce pressure because the combustion chamber volume is reduced. Peak pressure is related to the amount of powder burned and the volume in which it is burned. Burning the same amount of powder in less volume will increase pressure, burning it in more volume will decrease pressure, all other things being equal.

    The phrase "all other things being equal" is important. If one continues to decrease the jump to the point where the bullet is touching, or very close to touching, all other things are not equal. Touching the lands, or being lightly jammed (nobody can consistantly load bullets that are "just" touching the lands), will cause a significant increase in peak pressure of around 7,500 psi. A max load for a bullet with .020" jump is well over max with the same bullet jammed into the lands.

    Increasing seating depth from .020" or more jump to jammed into the lands will see a big jump in MV, and probably significant pressure signs, when the bullet touches and gets jammed into the lands.

    Another example of all things not being equal is if the case neck is too long. A case neck that is too long will be crimped by the begining of the throat and act to clamp the bullet in the case until a rather substantial pressure has built up. The effect is to reduce the combustion chamber volume by holding the bullet in place while the powder continues to burn. There have been some rifles blown up by this phenomena.

    Finally, powder combustion rate is a function of heat and apressure. Powders have heat/pressure operating reigons in which their combusion is stable. Increase the volume, or temperature, or both to move the combustion process out of this stable performance reigon and the combustion process gets erratic and unpredictable. Some pistol powders exhibit this phenomena more than rifle powders. W296, for example, is quite unstable if the pressure isn't high enough. In .357 magnums there is sometimes the warning to not use reduced loads with W296 and only one load, the max load, is given. Unique, a favorite powder of those shooting .45 LC in revolvers, operates best at relatively low pressures and can get erratic if pushed too hard.

    Finally, there is the issue of detonation that can happen when trying create reduced loads for subsonic bullet velocities, but that is unrelated to seating depth.

    And this just begins to touch on the complexities of what's happening in the brass during powder combustion.

    Fitch
     
  10. phorwath

    phorwath Well-Known Member

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    Fitch, have you ever tried it? I mean other than on the QL software?

    Below is a string of MV data from my 300 Win Mag with the bullet seated from 0.040" off the lands to 0.070" off the lands. Seating depth is increased in 0.005" increments. Two rounds were fired and chronographed per seating depth. MV drops with increased seating depth and reduced case capacity. So, the theory may sound great, but it's not reflected in measured MVs.

    Primer = CCI 250
    Powder = H1000
    Bullet = 180 grain Aluminum-tipped, Rebated Base Boattail

    I'm familiar with the natural gas law, and the Pressure/Volume relationship. But the natural gas law doesn't account for changing volume as the bullet moves down the bore, and the increased friction as the bullet enters the rifling.

    I'm also familiar with my chronographs and the results many others experience and report. [The first recorded MV at 0.060" off the lands (3035?) is in italics, because it's a questionable value. I run two chronos concurrently in tandem and the difference in velocities over the two chronos was skewed for that shot, meaning one of the chronos recorded a flawed value.]

    (0.040") 3024
    (0.040") 3021 Avg=3022.5

    (0.045") 3028
    (0.045") 3010 Avg=3019

    (0.050") 3021
    (0.050") 3022 Avg=3021.5

    (0.055") 3017
    (0.055") 3015 Avg=3016

    (0.060") 3035?
    (0.060") 3017 Avg=3026?

    (0.065") 3013
    (0.065") 2990 Avg=3001.5

    (0.070") 2999
    (0.070") 3001 Avg=3000

    You're aware of the freebore added to some of the Weatherby Magnum cartridge chambers? It allows additional powder to be placed in the cases, resulting in increased MV, for cartridges with bullets seated to the same depth in the cases - compared to chambers lacking the freebore.

    Kirby Allen has modified the throat design on some of his chamberings, allowing increased powder charges and MV, by allowing the bullets to transition into the rifling with less friction. He used a more tapered throat design.

    I'm aware of increased pressures created by jamming the bullet into the rifling.

    Now, with the bullets seated to already clear the lands, my guess is that giving the bullets additional jump into the lands by increasing seating depth reduces pressure and MV by reducing the friction (and associated pressure jump) as the bullet enters the rifling.

    I have read many experiences contrary to your statements, and the test shooter for the HATs bullets has repeated my experience of reduced MV with increased seating depths - over and over again. Very predictable in his rifles.
     
  11. jwp475

    jwp475 Well-Known Member

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    phorwath, You are only moving the seating depth .030 the opening thread was changing the seating depth by .200 which is quite a bit. The .030 that you are decreasing the seating depth is off set by the jump, but a .200 change may not be and that is what QL is showing. Pressure can increase past the MAP sometimes and not increase the velocity and sometime may acctualy decrese the velocity.
     
  12. Autorotate

    Autorotate Well-Known Member

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    This is what I see as well.

    When changing seat depth from the range of "at the lands" to .100 from the lands (in .020 increments), in two different chamberings, I've observed a decrease in velocity, with all other variables being the same.

    My theory, based on the observations from my experiences with those two chamberings and chrono data is the change in pressure as a result of reducing case volume, is much less significant, than the decrease in pressure due to the bullet being farther from being engraved by the barrel rifling lands.

    Until you load some rounds up, with safe charges, and go from "at the lands" to .100 from the lands, at your desired seating depth increment, and record the velocities.......you'll have a hard time convincing me otherwise that decreasing seating depth (in these ranges) doesn't decrease velocity.

    I've never tested this at greater than .100 seating depth changes....maybe that's where the decrease in case volume offsets the lower "start pressure" (QL term, but I'm talking real world shooting not powder modeling software) that decreased seating depths offer.

    Good discussion.
     
  13. Mikecr

    Mikecr Well-Known Member

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    Phorwath is right.
    The reason field velocities/pressures go down with deeper seating, is that EARLY pressure(peak) is reduced as you move from the lands. The latter having a greater affect(to a point), than the very tiny bullet displacement changes in seating.
    QL does not automatically compensate, but allows you to manually adjust for it, with 'starting pressure'. You should account for it with trial & error to match chrono velocities.
    If it seems to suck that you would have to do this, try it with ANY other reloading system...

    Thread starter, I'm curious, why did you change 'case length'?
    This is not usual, and in doing so you must also adjust 'case capacity' as appropriate.
    Again, this is a manual calibration.

    As painful as it may seem at times, the true value in QL is in it's CALIBRATED results. Nothing else provides this for reloaders.

    Other factors, some mentioned, are weighting factor, cross-sectional bore area, shank seating depth, starting pressure, powder temp, powder factors(per lot).
    There are a lot of little details to watch, the writer of this program has himself missed, and you have to catch them & correct them.
    Wrong bullet dimensions
    Inconsistent cross-sectional bore area
    Incorrect weighting factor(for cartridge)
    And factors not automatically updating with changes(like case length to capacity).

    So don't assume anything is actually correct until you've measured so across a chrono.
     
  14. Fitch

    Fitch Well-Known Member

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    I see the trend in the data but don't think it is statistically significant. In fact I can tell you for sure that differences that small determined from averaging two rounds are statistically meaningless. The data stream shows it rather clearly with the 3016, 3026, 3001.5 sequence. Shoot 8 or 10 at each seating depth, or better about 30 (which is close to the minimum for a good normal curve), and get the results where the uncertainty in the data doesn't exceed the claimed change and I'll go for it. The data shown is not compelling.

    My real concern is with pressure which isn't being measured. To convince me would require pressure measurements averaging a significant number of shots at different seating depths.

    What I do find compelling are the documented cases of firearms blowing up due to overpressure from bullets being pushed backinto the case. Those events have been documented and duplicated.

    We can agree to disagree about this.

    Fitch