Of Case Capacities, Bulk Densities, and Accurate Predictions

[hogan]

Perhaps didn't follow all your explanations here, but... did see something about working with an 8mm necked .308 case in an AR-15? A sentence or two later, discussing high grain weight values for CF223 and Reloader 17? Like a 62gr load of RL-17???

In an Armalite pattern rifle?
Talking maybe about a stretched receiver design based on AR-10 design and boltcarrier group?


Really think there is great concern for using any slower burn powder than Varget, RL-15, and those in same class as IMR 4064. Reloader 17 has some characteristics of real concern for employing with a gas-system AR-10...


Have seen many on this board treat loading for AR rifles, in terms of powder selection, as if data were interchangeable with that for bolt rifles. Maybe I missed your advisement that you are shooting a static bolt custom rifle w/o gas or piston operation?


Read over your first post in this thread to verify my comprehension, and see that you say you're using an AR-15 receiver...
Wow! what a monster case you must be using to get 60gr capacities.


Talking about densities; weight of water has no correlation to powder charge weight. The Lee manual #2 has case capacities for all ctgs covered measured in cubic centimeters, with CCs being a more uniform volume standard. The Lee measure set is also marked for CC capacity in newer production sets.


I don't really know that there is any "magic" to the weighting factor for powder charges. There are so many variables at play that are beyond rifleman's control, especially in match shooting circumstances. How does the heat retention of barrel and receiver affect performance at end of a string shot under time constraints? How does ambient temperature effect ignition variables? How do chamber dynamics affect case stretching upon chamber fill after ignition? Are you using personally selected custom bullets for perfect ogive consistency?

Handloading alchemy? Too many variables for it to ever happen.

 

[LHSmith]

Besides having to contend with keyboard shooters, now we are seeing the emergence of keyboard handloaders. How did millions of handloaders avoid blowing themselves up and before QL came along? (ans. = reloading manuals)
Still awaiting the "accurate predictions" as noted in the title. :

 

[gitano]

Hogan - Your points about the AR are well-taken. Let me elaborate.

1) You are right on about the AR 15! That was a typo. Thank you for pointing it out. I have corrected it to read "AR-10".

2) A am NOT using the AR platform in gas-operated mode. In fact, no gas operation hardware or modifications. No gas port. No gas block. No gas tube. In fact, I am removing the key so I can install a "bolt handle" for single-load operation instead of using the charging handle.

3) Chamber is cut with 7,62 NATO reamer, followed by a 9mm reamer for neck, followed by a custom-made (by Pacific Tool & Gauge) 8mm throating reamer. That sequence does indeed lead to a "large" case. In fact, the barrel starts out chambered in 8x63 Swedish, which in turn adds to the chamber's large dimensions.

4) The FINAL charges of CFE223 AND RL-17 are considerably lower than the figures I posted in the original post that I clearly stated produced blown primer pockets.

5) No alterations to the AR TEN receivers - either upper or lower - YET. I intend to mill a slot in the side of the upper to accommodate the bolt handle when I attach it.

6) With respect to your comment: "weight of water has no correlation to powder charge weight.": As stated, you are mistaken. There is a direct correlation that is a function of the volume of the cartridge case in units of weight per unit volume (the definition of density) and the density (bulk or solid) of the powder in units of weight per unit volume - same as in the case. Maybe you meant something other than what you wrote.

7) Different people use different terms differently. I use the term "magic" to describe something that has not been explained or is somehow as yet not fully understood. I do not believe in "magic" in it's formal definition. Arthur C. Clarke said: "Any sufficiently advanced technology is indistinguishable from magic." That is my intent.

LHSmith - I don't understand "Still awaiting the "accurate predictions" as noted in the title". By that do you mean you are waiting for something from me, or are you waiting for an accurate prediction from QL?

Paul

 

[LHSmith]

^^^^^ Well, you is the author of the thread.....tell us how to predict accuracy. But first tell us how you test, i.e. bench style, rest type, how you read conditions, # of shots per group, time interval between groups.
In other words, how do you reconcile what your "program" tells you is the optimum load? You do test don't you? Or does your interest lie only in the fact that the chosen load goes "boom" safely?

 

[gitano]

Hmm... I smell bait...

However, to explain MY intent with the use of the term "accuracy": I wasn't "predicting" accuracy, I was referring to accurate predictions. There is a difference. Clearly some don't understand the difference, so I'll explain.

QL makes predictions of muzzle velocity and maximum chamber pressure based on a variety of input parameters. There is a old saying in computer programming: "Garbage in; garbage out". This is true with any modeling program, and is certainly true for QL. But I digress.

With respect to accurate PREDICTIONS (as opposed to predicting "accuracy", which, by the way is the wrong term for how straight a firearm shoots): If QL predicts a MV of 2500 fps at a maximum chamber pressure of 51,000 PSI, it is trivial to determine the ACCURACY of that PREDICTION if one can measure the MV and chamber pressure. I have a variety of chronographs and therefore am capable of measuring muzzle velocity. I have the Pressure Trace system to "measure" (actually it's an inference of chamber pressure based on the expansion of a "standard" relative to known parameters, NOT a direct "measure".) If, using my hardware I MEASURE the MV of the charge QL PREDICTS will produce a 2500 f/s at a max chamber pressure of 51,000 PSI, as 2495 f/s at 51,250 PSI, then the QL PREDICTION is "accurate". If on the other hand, the actual MV is 2250 f/s and the max chamber pressure is 49,500 PSI, the the PREDICTION was NOT "accurate".

Therefore, neither QL or I claim(ed) the ability to predict "accuracy". However, I am perfectly capable - as are most folks - of determining if a PREDICTION of muzzle velocity or maximum chamber pressure is "accurate" or not, and THAT was the point of this thread.

Paul

 

[LHSmith]

(as opposed to predicting "accuracy", which, by the way is the wrong term for how straight a firearm shoots):



Paul

I'm afraid to ask for clarification on this, but perhaps theory dictates that I should be using a .220 Swift instead of a 6PPC.

 

[jimcasey01]

LHSmith do you have any direct experience with QuickLoad? I already know the answer no reason to give a response. If you were familiar with the program, you would not be making the statements that you are posting. If your theory dictates the use of a 220 swift, feel free to do so. Gitano is trying to share information with the rest of the forum that others may find helpful. It obviously will not help you.

 

[Nomad47]

LHSmith do you have any direct experience with QuickLoad? I already know the answer no reason to give a response. If you were familiar with the program, you would not be making the statements that you are posting. If your theory dictates the use of a 220 swift, feel free to do so. Gitano is trying to share information with the rest of the forum that others may find helpful. It obviously will not help you.

Well said, Jim.

 

[gitano]

I think my comment to Hogan (#6 in post #21), "You are mistaken" may have been too terse and didn't properly address his point about water WEIGHT and case capacity. The reason we can use the weight of water in density calculations is because of a unique characteristic of water. Namely, the DENSITY of water is 1 gram per cubic centimeter, "one". (A cubic centimeter is a unit of VOLUME and equivalent to a milliliter.) Since the density of water is ONE, we can fill an object with water then weigh the water in the object and since one GRAM (weight) of water equals one MILLILITER of water (volume), the VOLUME of the object in grams per cubic centimeters (or milliliters) IS the VOLUME of the object. Therefore,while it is true that the WEIGHT of anything OTHER THAN WATER would NOT allow us to calculate charge based on the bulk density of the powder (and its energy density in joules per gram), the weight of water does indeed allow us that calculation because its WEIGHT is linearly correlated to the volume it occupies with a ratio of 1:1.

Water is "magic".

Paul

 

[Brians356]

I:
1) measured the actual case capacity in grains of water, (53.9 - Notice how far off that is from "back-calculation" using bulk density.)

How did you measure the water capacity? Filled level with case mouth?

 

[gitano]

I:
1) measured the actual case capacity in grains of water, (53.9 - Notice how far off that is from "back-calculation" using bulk density.)

How did you measure the water capacity? Filled level with case mouth?

Yes, in a fire-formed case.

Paul

 

[gitano]

gstaylorg - I am probably the last person to suggest fixing something that isn't broken. Your process sounds to me like it isn't broken. That said, I understand your question regarding whether or not you are "leaving something on the table" with respect to "best use" of QL.

I think the apparent disparity in the NEED to get precise BD measurements and the process you use, probably exists, but is also probably only a function of the different goals the two of us have. While ultimately, I am looking exactly for what you are - the most precisely shooting load - I spend A LOT of time "designing" wildcats that suit my fancy at the moment. I will probably spend 10 times as much time in design as I do at the shooting bench. (LHSmith - You'll be wanting be sure to jump on that as "proof" of your 'suspicions' that I am really just a "keyboard" reloader.) When I get a rifle to shoot 1 MoA at 300 yds, I'm usually "done" with that rifle. I pretty much lose interest in it because I have achieved what I wanted to achieve: A rifle built by me, chambered in a new cartridge of my design, that I like shooting, and that is capable of all the precision one realistically needs (in my opinion), for Hunting. At that point, it's time for me to move on to the new challenges, which do not include winning a shooting competition or sniping at big game at 600+ yards. (I'm not suggesting or assuming those are your goals, just clarifying that they are not mine, and therefore I need spend no more temporal, financial, or physical resources on "tweaking" to shave tenths of MoAs.)

HOWEVER, I do NOT "calibrate" burn rates. That, in my opinion is truly 'playing with fire', and here are the reasons why I avoid that:
1) "Burn rate" is a non-linear function of pressure. Unless one knows ALL of the coefficients AND exponents of the mathematical model FOR THAT POWDER, "calibrating" the burn rate to a specific case and bullet is ALL you can safely do. ANY deviation in case capacity or bullet weight from that "calibration" and you are asking for trouble.
2) There are SO MANY variables in the internal ballistic equation, (and I am NOT talking about voodoo here), that effect the pressure/time curve that "calibrating" the QL burn rate using the method you do, is narrowly applicable in the extreme - THAT case, and THAT bullet and THAT barrel.

I suspect, that the "calibration" you perform with respect to burn rate is actually compensating for differences in true bulk density values of a specific powder. Personally, I would prefer to measure a parameter - like BD - and correct an incorrect value, than "adjust" a related sensitive variable - like burn rate. Putting in the measured value for a specific parameter means that parameter's value is applicable regardless of case capacity or bullet weight or barrel/chamber. "Adjusting" the value of an parameter whose determination is unknown is specific in the extreme.

I believe the example I gave in my original post where I "calibrated" the case capacity based on back calculating from the case capacity of actual powder is a perfect example of the errors that can be realized by such "calibrations". The "calibration" I performed was "fine" until I changed bullet weights. Then it went to hell. The reason it did is because the mathematical function associated with pressure (and including burn rate) is non-linear and is different with different bullet weights, etc. So while "correct" in the instance, it was not appropriate to "wander" like I did. I assume you do not "wander" from the initial conditions (average case volume, bullet weight and barrel) you use when you calibrate the burn rate.

Let me repeat for emphasis: I have NO DESIRE to "change your mind" about the process you use to achieve your goals. If it ain't broke, for goodness' sake don't fix it! AND, my comments are not just about not having to weigh water to determine case capacity. I could not agree with you more that I find that activity "no issue". Rather, my comments with respect to measuring bulk density and entering the true value into the QL model, is with the intent to diminish "garbage in: garbage out". If you're getting "gold out", believe me when I say I'm "with ya".

One final on topic comment: As I read and understand your process, I don't think the process I described is more tedious, but I could be seeing something operationally in your process that isn't there.

By the way, it is genuinely pleasant to hear of people that are able to get QL to work for them as well as it has worked for me. Thanks for that!

Paul

PS - I get essentially the same OBT results you do. Namely, the OBT "sweet spot" is actually between 1 and 3% down in charge weight for wooden-stocked, bolt action rifles. For rifles configured with "floating" barrels, like on the AR platform, I find the OBT sweet spot to be VERY wide. Almost to the point of insignificance. I know. THEORETICALLY the "floating" barrel shouldn't matter to the WIDTH of the OBT sweet spot. I understand. That's just not what I'm actually SEEING!

Paul

 

[mikecr]

I agree that it's better not to lie to QL, as it's better not to lie to external ballistic software.
Seems to me that measuring and correcting BD is one way to correct a local factor. I like it.

The discussion went outward to weighting factor for a while. This is not at all connected to attributes of powder, but of cartridge design.
A cartridge(like a 6Daser) that better contains powder burn INSIDE the chamber, gains efficiency(all else equal).
In contrast, a cartridge(like a 30-06) that pushes a slug of unburned powder, adding to bullet mass, is less efficient, recoils more, and produces higher muzzle pressures.

But weighting factor is of course -just one factor.
High peak pressure(like in a tiny 6PPC), where viable, works around a lot of internal ballistic issues.

 

[savagedasher]

Several months ago we had a article about how to measure case capacity.
Ball powder H380 was the ticket . I did 10 then used a long drop tube on the same 10. I didn't get the same results both ways, with the long drop tube I had to add over a grain more powder to get the same fill. Larry

 

[gitano]

I feel compelled to report some new information that renders much of what I wrote in the original post, moot.

Since I just purchased a pound of Vihtavouri N-133, I decided to report the difference in actual Bulk Density (BD) and QL's value for BD AND show how that difference effected QL's estimates of charge and max pressure. To 'cut to the chase', it didn't make a damn bit of difference! The Load Density changed, but QL predicted EXACTLY the same charge for each of three values for the BULK density adjusted powder.

What this demonstrates is that QL is NOT using Bulk Density for ANY part of the charge calculations except load density.

This is disappointing, but it is the reality. It also means that we have to resort to methods similar to those suggested by gstaylorg: Adjusting burn rate (or other parameters) until the predicted muzzle velocity matches the measured muzzle velocity. That is dissatisfying (and disappointing), because without very specialize equipment, we 'regular Joes' have no way to measure ANY of those factors.

Don't get me wrong, but "back-calculating" is not "calibrating", and is fraught with risk unless constrained to very specific circumstances. In other words, it is NOT a calculation about a powder, it is a calculation about a powder in a specific case using a specific bullet in a specific rifle. It "works" within those constraints, but requires one to repeat the "adjustment" for any and all changes to the conditions in which the first adjustments were made.

It also eliminates accurate PREDICTION. In fact, it eliminates all but the grossest "predictions" at all. I'm quite disappointed.

Paul

PS - The reason adjusting the BD has actually mattered in some of my loads is because I often load to estimated load densities of 105% of case capacity. When I changed the BD I changed the powders that "fit" in the case in question and therefore even showed up in the powder selection table.

paul

 

[fredo]

Interesting discussion, enjoyed the read. I agree with the "garbage IN/garbage OUT" analogy.
I'm of the opinion that all we as reloaders/wildcatters can do, is input the most accurate & repeatably consistent data to QL and see what we get. From there on out, certain 'tuning' might be necessary to mirror what the chrono is telling us. From there on out, systematic load testing on target using QL derived baseline data will always be the "tell all" indicator of accuracy...

On the topic of Ba, I've noticed that adjusting the Ba value to 'tune' a specific powder for one particular bullet/cartridge, that adjusted value has proved viable when using that same powder in an entirely different bullet/cartridge. IE, the adjusted Ba value for that particular lot of powder appears to hold true for more than one specific load recipe...

To that end, my opinion is that carefully tuning Ba is more about adjusting QL to better address any variance in the burning characteristics of THAT particular lot of powder. Taking QL's pre-set values for burn rate can amount to "garbage IN", and tweaking Ba to match measured velocity seems to nip that right in the butt...

Questions: how are you all measuring to input for the "barrel length" parameter? Boltface to muzzle? Case mouth to muzzle?
How precise are you being with that measurement... to the nearest 0.1"?

And for those using Ba to 'tune' to measured velocity, how closely are you trying to match actual MV? +/- 5fps fro the mean MV? 10fps?
For those using chronos w/screens, are you matching to the measured speed at the screens, or derived velocity from the actual muzzle? When using a Magnetospeed chrono, measured MV is actually velocity at the muzzle, not 10-15' downrange at the screens. Is anyone accounting for that when 'tuning' Ba to match MV?

Answers to these questions all factor into the data used for QL, just addressing the quality & consistency of it. For discussion...

 

[gitano]

My use of QL is PRIMARILY as a starting point for load development. However, the closer one gets in that initial stab at reality, the less time, and money one needs to waste finding the true 'sweet spot'. Looking for perfection "right out of the box" is unrealistic. However, there are circumstances in which "perfection" has been close with QL. Those outcomes just seem to be getting fewer and fewer the more I use it.

Secondarily, but a close second, I use QL for wildcat cartridge design. As such, I need/want to be as close to reality as possible BEFORE I ever pull the trigger on a new design. This issue with bulk density, substantially reduces QL's usefulness in to that purpose. Hence my disappointment.

With respect to an adjusted Ba fitting beyond the conditions under which it was adjusted: There is not doubt that the adjusted value may fit in other similar bullet weights and designs on the same case in the same gun, and even possibly in different cases in different guns. BUT... The burning rate (Ba), is only ONE of SIX parameters QL uses to determine the charge and subsequent max pressure. Since we can't measure (easily) any of those six - which means we're basically just turning a knob that we know nothing about - we might as well choose any one of the six. There is no reason to choose one over the others. Furthermore, what about when "it doesn't". We can never know when that particular case might rear it's ugly head.

With regard to measuring barrel length: The BATFE says the barrel length is from the bolt face to the muzzle. QL subtracts case length from the "bullet travel" calculations. Therefore, I measure from the bolt face to the muzzle to the nearest 0.1". I'm not arguing that is "correct", rather just reporting what I do in response to your question.

Since I have yet to adjust Ba so that estimated MV equals measured MV, I cannot answer your other questions. HOWEVER, if I do decide to do that or modify one of the other parameters, I will adjust it until it matches the AVERAGE MV EXACTLY. I don't see a reason not to do that since I'm doing nothing more than "turning a random knob" on a mathematical calculation.

Paul

 

[CharlieNC]

Working up loads for new a 223 the actual velocities were slower than calculated for low charges, but faster for the higher charges. Adjusting Ba drives velocities only one direction across the entire range which is a clear example of the importance of all of the other parameters as well.

 

[Nvreloader]

Gitano

You mentioned that Hartmut Bromel has a site,
can you please provide his site so I can read the info on it?

Tia,
Don

 

[Brians356]

I:
1) measured the actual case capacity in grains of water, (53.9 - Notice how far off that is from "back-calculation" using bulk density.)

How did you measure the water capacity? Filled level with case mouth?

Yes, in a fire-formed case.

The reason I asked was some hereabouts believe water capacity level with case mouth will be too light for QL.