Getting higher velocity than predicted by QL
- Thread starter uncle-buck
- Start date
Thanks for all the replies.
I must be doing something incorrectly.
Bullet is .308 Sierra GameKing 180 gr. SBT
Cartridge length is 2.873"
Case length 2.005"
Barrel length 22"
Case capacity is 54.9 gr. of water.
Weighing factor is 0.53
Bullet is seated 0.018" off the lands, so shot start pressure should be 10,299 psi, is that correct?
Powder charge is 40.5 gr of IMR4064
Actual MV is 2546 fps
Ba was adjusted to 0.636 to equal actual MV.
*But* that produced an excessive projected Pmax of 62,781 psi in QL.
Load shoots great with no signs of excessive pressure and is well below Sierra's published max. load.
What am i missing?
I must be doing something incorrectly.
Bullet is .308 Sierra GameKing 180 gr. SBT
Cartridge length is 2.873"
Case length 2.005"
Barrel length 22"
Case capacity is 54.9 gr. of water.
Weighing factor is 0.53
Bullet is seated 0.018" off the lands, so shot start pressure should be 10,299 psi, is that correct?
Powder charge is 40.5 gr of IMR4064
Actual MV is 2546 fps
Ba was adjusted to 0.636 to equal actual MV.
*But* that produced an excessive projected Pmax of 62,781 psi in QL.
Load shoots great with no signs of excessive pressure and is well below Sierra's published max. load.
What am i missing?
Ned Ludd
Silver $$ Contributor
BCBRAD - Just out of curiosity, where did you find this reference/instruction?
To the OP - Quickload can only process the data you input. Further, all the vaules you will find in various pull-down menus (i.e. powders, case volumes, etc.) are estimates at best. Chances are very good that your actual case volume will not match the QL .308 Win SAAMI spec. Nor will the burn rate of the actual Lot of powder you're using. The values you determine empirically may be close, they may even be quite different. That is why you should NEVER use Quickload to point you at a full-pressure load right out of the gate. Alwasy start with some load that is reduced by some factor below MAX pressure until you KNOW where your powder burn rate and case volume fall relative to the QL preset values (i.e. "calibration").
To "calibrate" QL, I always begin by
1) Setting up a new file with the best possible inputs I have available:
For example, the case volume for the majority of different Lots of Lapua brass I have used don't vary all that much; they are certainly much closer to one another than the QL preset case volume, which is quite different than any brass I have ever used. So I input the measured case volume for a current or previous Lot of brass, barrel length, bullet OAL, and case trim length (each of which which I can directly measure).
2) Next, I adjust the temperature to approximately what I expect it to be when I will shoot the loaded rounds.
Other than temperature, I don't alter any other part of a preset powder file (i.e. leave burn rate alone for the time being).
3) Find the charge weight (in gr) associated with SAAMI MAX pressure
4) Reduce that charge weight by at least 2 to 5%
5) Load 10 rounds at that charge weight, use at least 5 to obtain an "average" MV
6) At home, determine the actual water volume of your fired cases, inputting the value into
your QL file
7) Adjust the burn rate factor (Ba) for your selected powder at the appropriate
temperature until the predicted velocity exactly matches the average velocity you just
determined using a known charge weight.
8) Re-save the QL under a new name, such as "Calibrated" or similar.
You have now adjusted/calibrated your QL file for your specific setup to return your exact measured velocity for a given charge weight. You can now adjust charge weight and the program will give you reasonable velocity/pressure estimates over a fairly wide range. If conditions dictate, you can alter the temperature, COAL, bullet length, or other parameters in the program.
By nature of how it works, QL predicts fairly linear responses for variables such as pressure and/or velocity. However, as pressure and/or temperature increase, so will velocity, and past a certain point, we know that real world changes are not always linear. The closer your "calibration" charge weight and velocity are to those of your final working load, the closer the predictions will be to your actual results. Another way to look at it is that the farther away you are (or the larger the change you make to a load), the less certain the QL predictions will be. You can thus "re-calibrate" your QL file with any new data set as needed. But I would always recommend starting out with some kind of calibration approach using a reduced load. That way, you're less likely to get any potentially ugly surprises because your cases have really thick walls (i.e. low internal volume) and you're using a Lot of powder with a really fast burn rate.
Ned Ludd
Silver $$ Contributor
If I'm following your numbers correctly, start pressure should be the default of 3626 psi unless you have changed it for some reason. I never change the default shot initiation pressure unless jamming bullets as described in the QL manual. So, you're adding an extra (10,299 - 3626 =) 6673 psi in there somewhere. If you increase the start pressure, so goes the final peak pressure, which can make it look as though a load is way over pressure when it actually is not. L would suggest leaving start pressure at the factory value of 3262 psi unless you have a good reason to change it, such as a jammed bullet. My QL data are generally spot on without having to change that value.
I changed shot start pressure based on a previous comment which said to add 7200 psi for a jammed bullet and then subtract 146 psi for each .005" off the lands.
When using the shot start pressure default value of 3625 psi and adjusting Ba to 0.6615 to equal the actual MV of 2546, the calculated Pmax value is 58,368 or 94% of SAAMI max.
Does that appear reasonable to you? Thanks
If the start pressures are those when the bullet starts moving, consider this fact.
A 30 caliber bullet that needs 5 pounds of force to move it forward in the case neck will start moving when pressure in the case is 67.11 psi.
So, if you are 0.030" off the lands the start pressure will not be 10,096 psi for a 30 caliber bullet. Force on the bullet would be 752 pounds.
A 30 caliber bullet that needs 5 pounds of force to move it forward in the case neck will start moving when pressure in the case is 67.11 psi.
So, if you are 0.030" off the lands the start pressure will not be 10,096 psi for a 30 caliber bullet. Force on the bullet would be 752 pounds.
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The start pressure is the resistance met by the bullet entering the rifling as well as the bullet release from the neck resistance.
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The actual working cartridge volume (H2O) with a seated bullet is determined ,ultimately, by the seating depth of the bullet. However, the effective volume of the case must include the freebore.
So, if we take the pressure to overcome a jammed bullet (7200+3625=10,825) subtract the freebore in thousands of inches you will find the effective case volume, that numerical volume is not listed. The bullet is running ,basically , resistance free until it hits the rifling.
If you are 0.100" off the rifling you reduce the jammed start pressure by 0.100"/5=20. 20x146=2920lbs. 10,825-2920= 7905 lbs start pressure.
Velocities are corrected by adjusting Ba, but only up to 5%.
I find the inputs better if you manually measure bullets, cases, volumes etc. Weigh powder to the nearest 0.02gn as well.
Adjust powder charge to get an OBT while maintaining the predicted velocity.
I don't know.
What I do know is the method I describe and the manipulation of QL gets me very accurate ammo.
Even if it takes 70 pounds of force to move it in the case neck?
It's about 16,000 fps in chrome moly according to data I've seen.
Yes, I started reloading in 1999 and bought QL in 2000.
1) My jug of H4350 needs a 4% powder charge addition entered [Jug is 4% slow] to get QL to agree with chrono. with multiple different cartridges.
OTOH My jug of Varget is always perfectly predicted by QL with multiple different cartridges.
2) Start pressure is ~~ 2kpsi for not touching the lands, and ~~4kpsi for jammed into the lands to get QL to agree with chrono
3) I have loaded a box of 7mmRM ammo and taken it to the range with 2 rifles with 24" barrels. There can be a difference of 200 fps between chrono averages.
Ned Ludd
Silver $$ Contributor
Uncle-Buck: according to the QL manual, you add 7200 psi for a jammed bullet. That value has always seemed high to me, and put me in a position similar to yours in that QL was predicting pressure well over MAX, even though I wasn't getting any pressure signs or problems with brass life. For that reason, I have done some experimentation to estimate the increase in pressure due to a bullet seated into the lands. As far as I can tell, QL's use of the term "jammed" means a hard jam, possibly as far as .020" to .025" into the rifling. I can certainly understand why that might increase start pressure by 7200 psi. However, most of us that seat bullets into the rifling aren't using a "hard jam"; more likely somewhere in the neighborhood of .005" to .010" into the lands. In my hands, seating a bullet .005" to .010" into the lands is estimated to raise start pressure only by somewhere in the 800-1000 psi range. In other words, the increase in pressure as a bullet is seated farther and farther into the lands is not linear.
The bottom line is that anyone using QL can fiddle around, tweaking different aspects of the inputs to come up with adjustments so that the QL predictions match their observed velocity and drops. As someone new to using the program that is trying to set up user files for the first time, I would NOT recommend doing anything beyond what the user manual suggests until 1) you determine how well the QL outputs match your observed data and 2) you gain a little more familiarity using the program.
As far as comments from BCBRAD above - the effective working volume of a case is determined in QL from the dimensions in the selected bullet file, selected cartridge file and/or case length + actual case volume inputs. The program doesn't care how long the freebore of the rifle is, because it doesn't know. It only knows the seating depth and the overall effect on internal case volume based on the bullet selected. The change in pressure as bullets are seated farther and farther out in the case is determined primarily by three variables, friction, the change in effective case volume and resistance to movement as the bullet touches/enters the lands. The effects of these variables are not uniform as the bullet is seated deeper and deeper into the rifling until a "hard jam" is reached. As I suspected, the math given above for estimating pressure variance due to freebore length is simply some made up formula. It might appear to work, but it in no way reflects what is actually occurring when we actually pull the trigger, nor is it a good way to make estimates of pressure. As I stated previously, it is very likely that the increase in pressure as we seat bullets into the lands is not linear with respect to distance. Further, the length of freebore doesn't need to be divided by anything simply because once the bullet starts moving, the resistance to movement will essentially add very little pressure at all until the the rifling is reached (i.e. - once the bullet is moving, it doesn't really matter whether the freebore is .050" or .250", neither one is going to add much in the way of pressure to the total. In fact, With either freebore, the start pressure should remain at the default setting of 3626 psi, not have some fraction of the "jammed" start pressure added. The bullet isn't jammed, it's not even touching the rifling, why increase the pressure over the preset standard value at all? For bullets NOT seated into the lands, regardless of freebore length, there is simply no reason to do anything with the number for increased start pressure (7200 psi) with jammed bullets at all. All that ends up doing is markedly increasing the start pressure and the the peak pressure, making it appear as though a given load might be overpressure when, in fact, it is not. Use the 3626 psi preset value until a bullet is seated into the lands, regardless of the length of the freebore or how far off the lands the bullet is seated. The program already calculates change in pressure due to any change in case volume due to a change in seating depth. At that point, you can decide how much to raise start pressure between zero and a "hard jam" (+7200 psi). As I stated before, it's unlikely to be linear, but that's something that needs to be determined by the end user with their specific setup.
It's a free country, anyone can do whatever they like with QL and adjust it in whatever fashion they see fit. However, new users of QL need to be very cautious when seeking advice on how to adjust the program. IMO - your best bet is to start with the manual, not someone's made-up formula from the internet. The start/initiation pressure represents a significant amount of the peak pressure and can therefore have a very dramatic effect on peak pressure when using QL. If a mistake is made, the effect can go either way; a load that is predicted to be way over MAX pressure, but actually isn't, OR a load that appears to be safe, but might actually be several thousand psi over MAX. Why risk that?
Ned,
Many thanks for the QL calibration tutorial and your comments.
Attached is the QL output for my .308 Sierra 180 gr. SBT hunting load.
Does it look correct to you?
The projected Pmax is about 94% of SAAMI Pmax and would only exceed it at about 111F, everything else being equal.
With respect to the QL manual, I have found it to be content rich, but not particularly organized for easy reading by yours truly. So, your advice is much appreciated.
Am packing for a South Texas hunting trip, so apologies for the brevity of this message - and thank you again for all of your help.
Bert
Many thanks for the QL calibration tutorial and your comments.
Attached is the QL output for my .308 Sierra 180 gr. SBT hunting load.
Does it look correct to you?
The projected Pmax is about 94% of SAAMI Pmax and would only exceed it at about 111F, everything else being equal.
With respect to the QL manual, I have found it to be content rich, but not particularly organized for easy reading by yours truly. So, your advice is much appreciated.
Am packing for a South Texas hunting trip, so apologies for the brevity of this message - and thank you again for all of your help.
Bert
Ned Ludd
Silver $$ Contributor
Plugging in your numbers but with the default weighting factor of 0.50, the calibrated output I come up with is very similar to yours (see attached file). It is not identical in terms of pressure, but pretty close.
The two things that caught my attention were your case volume (54.91 gr, which seems relatively low), and the amount by which you have to adjust Ba to match your actual velocity (~8.9% increase). The "low" case volume may simply be inherent to the brand of brass you're using, especially if it has noticeably thicker walls than Lapua. More importantly, increasing the case volume value in the program would effectively lower pressure and require an even larger corrective increase in Ba to match the predicted and actual velocities. I have previously encountered similar QL predictions where I had to change Ba by more than 5% in order to get predicted and actual velocities to match.
It is not "ideal" to have to change Ba by that much, but when doing so, I have never had a problem when making subsequent changes to charge weight with the predicted velocity not matching the QL prediction. It cannot be ruled out that you have a batch of 4064 that is at the upper end of the burn rate range for that powder. Alternatively, there could be another reason that is not immediately clear. Was the temperature exactly 70 degrees when you measured velocity? What type of primer are you using? Another possibility is that a primer with significantly greater brisance can markedly increase velocity over a another brand of primer, even with the exact same charge weight of powder
Regardless, as long as predicted velocity matches measured velocity fairly closely over a range of charge weights, I work under the assumption that other predicted parameters such as fill ration, pressure, and barrel time are accurate within the limitations of the program. Your QL predictions fall well within the range at which I usually obtain optimized .308 loads in terms of pressure. That is to say, loads with predicted pressures in the range of 57-58K psi. With standard .308 brass, loads predicted to be in the 59.5-61.5K psi or so range, although still below SAAMI MAX, are generally hard on brass and may cause the primer pockets to become unusable after as little as 4-5 firings.
At this point, I would not be greatly concerned that your velocity is quite a bit faster than predicted by QL using only the default IMR 4064 powder input for temp and Ba. I have had plenty of Lots of various powders that gave velocities very close to those predicted using the preset Ba. But I have also had Lots that were in the neighborhood of 75-100 fps fast/slow. During load development, I generally aim for Optimized Barrel Time nodes whenever possible, using barrel times from Chris Long's OBT chart and those predicted by QL. In my hands, accuracy nodes on paper fall very close in terms of barrel time (as predicted by QL) to the values in Chris Long's table. Other factors, such as brass life, also seem to mirror the pressures predicted by QL quite well. As long as the velocities predicted by QL following "calibration" of the program for your specific setup match reasonably well, I see little reason not to accept the other outputs such as pressure and barrel time as being valid, or to go to great lengths by changing a number of other parameters in the program merely to improve the output by a negligible amount. QL outputs are, by definition, "estimates" or "predictions". They are certainly useful for expediting the load development process, but their true "accuracy" must always be questioned, and they can never replace the outputs of targets generated by actually testing various loads. In other words, the test targets should always have the final say. Once I am convinced that the target is telling me I have a good load, as long as the predictions in QL seem to match reasonably well with actual measured data, I don't feel the need to adjust the program further. IMO - you're really just tweeking factors that are already down in the noise at that point.
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Remember QL for their own legal protection would have to show warnings for anything over factory specs. Let your rifle tell where to stay safe but remember hotter temperatures means higher pressure. When you reach pressure you will have bolt lift tightness but remember if its too much your bolt wont open. Then comes the rubber hammer. Keep an eye for extraction marks
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