Quikload start pressure

Discussion in 'Reloading' started by trueblue, Jul 26, 2009.

  1. trueblue

    trueblue Well-Known Member

    Feb 18, 2008
    I am using Quikload, and am doing load developement using a starting pressure of 10,800 psi because of loading Berger's just touching the lands.
    My question is how far off the lands do I need to be in order to be able to use a start pressure of 3625 psi ? Would 0.002 off the lands bring the pressure down or do I need to be farther off the lands than that ?
  2. pressman

    pressman Well-Known Member

    Mar 14, 2008
    not to rail road your thread but i also have a pressure question. starting at the lands or close to the lands. if you shoot 1 or 2 rounds close to or at the lands if find that i always get one flier out of a 5 shot group and usually it is the 4th or 5th shot. i always thought it was me. but i had a guy tell me it was because i was right at the lands and after a few firings and the barrel warmed up at the throat i was getting different pressures than i was with the first 1 or 2 rounds.
    so i am too interested in knowing how to find how close you are to the lands equals a pressure reading. just like true blue .002 = X pressure or .010= z pressure. and what really is making the pressure or intense or less? i do know after i started seating my lapua bullets .015 or a little more my fliers left and have never came back. just would like to know why?

  3. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003
    The beauty in QL is that it CAN be calibrated, which cannot be done with load manuals.
    The downside of QL is that it MUST be calibrated. So it's no more accurate than your inputs.

    With tool tips enabled, and starting pressure selected you see a note about adding 7200psi for bullets touching the lands. This is a starting point. Load a few, shoot over a chrono, then calibrate QL.
    Starting pressure is one adjustment to dial in the software.
    There is also, weighting factor, bore area, case capacity, case/powder fill, seating area, powder temp, and powder lot/file adjustments.
    None of which is accounted for in manuals...

    Once it's calibrated you store that load, for that gun, and future predictions will be amazingly close provided you change only one or two things at a time.

    To directly answer your question though, there is no way to exactly PREDICT your pressure curve(Beginning, middle, or end). No rules of thumb can apply with any precision, because no two barrels are the same.
  4. Autorotate

    Autorotate Well-Known Member

    Apr 2, 2007
    Re: Quickload start pressure

    This is the 65K dollar question. I've struggled with this myself, and have concluded that each rifle will be different, as the "start pressure" captures effects from more than just distance from lands, but neck tension, throat design, lead angle, and tightness of bore......

    I have found Quickload to be most accurate when you can load a string of rounds (obviously the more the better i.e. 10 rounds) at varying charges, that are all shot/loaded with all other factors being the same (primer, powder, brass, neck tension, distance from lands, bore condition) and then recorded those 10 velocities over a chrono. If two or three of those charges were near the "max load" for that gun, I find that helpful for the next step.

    Step 1-(collecting range data)-Load 10 rounds at varying charge weights/steps, with all other factors being the same i.e. COAL, primer, powder, neck tension, case prep on cases, brand of cases, number of firings on cases, bullet. Collect your chrono data, and ensure you correct for chrono distance from muzzle to have true corrected muzzle velocity.

    Step 2-(initial input setup of Quickload for the range data)- Back at the computer we'll now attempt to calibrate Quickload to your gun. First input the temperature of the cases when they were fired. (see note 1 below)

    Once the temp is plugged in, we ensure the COAL, barrel length, and case weighing factor all correspond to your rifle and case. (see note 2 below)

    Step 3-(Low/Slow load) Now plug in the lowest charge weight, and a nominal start pressure (the ones suggest by QL are excellent suggestions). If the velocity is lower than what the corrected chrono muzzle velocity is, increase the start pressure to make the velocity match in QL. If QL was faster, lower the start pressure. I would use 1000 psi increments. Once you have QL matching with your low/slow load, move to the next step-

    Step 4-(High/Fast Load) Now input the highest charge weight, with the same start pressure/case weighing factor that you used on the low/slow load. Does the velocity match? If not...here’s where the “magic” from you comes in. You’ll need to adjust the case weighing factor and the start pressure so that QL can accurately predict the velocities at both the high/fast load and the low/slow load.

    Use of the following rules of thumb can be helpful. For a given set of conditions:
    1. Raising start pressure will raise velocity and peak pressure and vice versa
    2. Lowering the case weighing factor will increase velocity and lower peak pressure and vice versa.

    Conclusion-This can take a bit of time. But for your investment of time, you’ll be able to plug in all the load step/increments from your shot string, and QL should be spot on. Additionally you’ll have a great place to start regarding start pressure/case weighing factor for other powders.

    If you can’t get the QL prediction to line up on both the slow/low and high/fast load with the same start pressure/case weighing factor, you likely either have a ES with your loads or a chrono problem….don’t ask me how I know:( I now shoot with my CED M2 at least 25 feet from the muzzle:)

    There’s probably a simpler way to do this…but using this method, I’ve found QL to be very accurate and helpful, and to be a great predictor of velocity potential and where “high pressure” loads might be encountered when desiring to develop another load for a different bullet or powder.

    Hopefully this helps someone else. QL is a great tool.

    Note-(On Temperature)-This may be different than the range temperature, i.e. if your rounds sat on the dash on the way to the range, they were sitting in the hot sun for 1 hour during your session, you allowed the loaded round to sit in the chamber for extended periods prior to firing...etc. I use the ambient range temperature if the round goes off in 15-20 seconds from firing, and I've taken care to keep the rounds in the shade prior to firing. I've also used a small lined lunch box cooler with a bag of ice, not as attempt to keep the rounds "cold" but to keep them at a constant temp prior to firing.
    I know some folks will say the effect of temperature on the powder/velocity is negligible, and those opinions are from very qualified folks that I respect, that hasn't been my experience. IME, Temp has effected all powders (even H1000) especially once temps go over 80 degrees F.

    Note-(On case weighing factor)-.40 case weighing factor has proved to be fairly proven for the .338 Edge. I use .36 for a 300 RUM Improved at it's works well. This weighing factor should get you started for your case.