Calculated velocity change caused by a single granule of Varget in a .308/175gr.

[M14AMU]

I think you're getting the cart ahead of the horse till the case capacity is all the same it can't be determined accurate. Larry

Was wondering if anyone was going to broach this subject!! ;D

 

[jlow]

I think you're getting the cart ahead of the horse till the case capacity is all the same it can't be determined accurate. Larry

Was wondering if anyone was going to broach this subject!! ;D

Case volume in real life of course affect MV, but realistically when you are looking at the numbers Boyd is dealing with here, it is not going to make any difference.

After all, we are talking about 1 granule giving something like 1 fps +/- 0.1-0.2 fps which is a 10-20% variation ;D. The key here is as Boyd said, he is just trying to see what those numbers look approximately like.

 

[dmoran]

Powder speed is one of the productive data byproduct's of incremental ladder testing.
Which is true/factual data to the actual rifle/barrel/bullet/powder/primer/capacity being tested.
There can be substantial variance in powders sensitivities from Lot to Lot, that warrants independent testing - IME
Donovan

 

[Macropod]

I use an A&D FX120I for my powder weighing and have wondered the what small powder variations would do to velocity. So thanks Boyd!

I wonder what very slight changes in primer brisance would make. That would much harder to predict I imagine.

Long range performance is all about consistency.

 

[ebb]

It all seems so important and it is to get the best load possible. But it doesn't really when you look at what the wind will do to it in the long slow flight a 308 makes to get to 1000yds. I guess we want to fix what we can, and I see you are trying to get him to fix something that matters more. I just keep having dreams of a short mag case necked down to 22 caliber with a 3 inch long bullet that has a really high BC, and a long barrel life.

 

[BoydAllen]

dmoran,
I am absolutely in favor of testing. I was just trying to get him to focus on what is likely to be more important, and came up with some numbers that I thought worth sharing.

 

[amlevin]

I just keep having dreams of a short mag case necked down to 22 caliber with a 3 inch long bullet that has a really high BC, and a long barrel life.

Try soldering together two 1.5" Flat based bullets so you have a point on each end. That would give you a near perfect Sears-Haack body. Theoretically there is no more perfect aerodynamic shape than that.

Unfortunately you may need a case with a really long neck to hold it 8)

 

[Ken Dickerman]

gstaylorg,
100% agree. I don't believe weighing to 1 kernel makes a difference at 1,000, but with my procedure it's what I get, it's as fast as weighing in bigger increments, and I like it.

 

[jlow]

Of course the way I look at it is all these small differences that does not make a big difference by themselves can add up if one started to ignore/skip doing multiple accuracy related things like consistency in bullet base to ogive, case weight/volume, etc.

 

[savagedasher]

I think case volume is has more of a difference then one kernel of powder.
if you want to check it take two random cases and load each one . to the exact kernel
Load each one with one kernel more and record the speed of each .
That will tell you . Larry

 

[BenPerfected]

Of course the way I look at it is all these small differences that does not make a big difference by themselves can add up if one started to ignore/skip doing multiple accuracy related things like consistency in bullet base to ogive, case weight/volume, etc.

I like Boyd's process of working to calculate that each kernel of Varget variance = approx 1 FPS. Has anybody tried to measure the impact of case weight/volume or the bullet base to ogive impact....on what?
Ben

 

[JarheadAZ]

The thing about small variables is that it is not advisable to assume they exhibit either a plus or a minus in combination with all the other variables, quantifiable or not, on the overall accuracy scale.

At such levels of relevance, we could be talking akin to deciding how many angels can simultaneously dance upon the head of a pin...

Greg

 

[BoydAllen]

Again, all I was attempting to do was to assign relative importance to small differences in powder charge so a shooter would not become too obsessed with a variable that was not all that significant in his effort to sharply reduce an extreme spread in the range of 40 FPS. I think that I accomplished that. It has been my experience that people tend to focus too tightly on the things that they have the best equipment to measure. I have done the same thing. If we have concentricity gauges we strive for perfection in that area, because it is easy to measure what is going on. The same is true for things like powder charge, even when we are not competing at ranges that would require such precision. What is harder to quantify is variability in how a bullet is released. We look at the difference in the neck diameter before and after seating, but in fact there are multiple factors at work, some of which we may not even be looking at. For example, years ago, one successful 1,000 yard shooter told me that as a final sizing step for his brass he uses an expander mandrel and die, and has a set of expander mandrels graduated in half thousandths. He said that he believed that it gave him a more consistent result. How many would have even thought to try that? Then there is the issue of the consistency of the coefficient of friction of the inside of case necks, which can be further complicated when annealing and/or cleaning with SS pins come into the picture. It goes on and on. I have not been on a ES quest in my reloading because I do not shoot at distances where that is a major factor. On the other hand, when I chronograph loads I have not seen numbers that cause me to be concerned. My friend has different ambitions.

 

[Brians356]

I would only worry about small amounts of powder variance after all of the bullets had the same feel when seating, and my ogive to head dimensions were very close to perfect.

Not to trigger a range war, but only as an aside and FWIW, the approach to neck sizing and "feel" seating that Virgil King developed is still worth re-reading, if only for a sense of perspective. I admire such attention to detail if nothing more.

 

[Brians356]

Try soldering together two 1.5" Flat based bullets so you have a point on each end. That would give you a near perfect Sears-Haack body. Theoretically there is no more perfect aerodynamic shape than that.

That's called a " pushmi-pullyu" bullet. First record of one is from ancient Greece, but it was used for something else then.

 

[NevadaZielmeister]

No, I do not know of such a chronograph. I was trying to show the potential improvement of going from the accuracy of a Chargemaster to that of charges trickled onto something like a Gempro 250. If we estimate the Chargemaster as being at +- .1 grain, and the Gempro at +-.02 the difference would be around 6 FPS in ES. That will not get you to low double digits from around 40.

You know Boyd, I see what you were doing and it is a good lesson. However, I wish you could have gone further in telling him the the Gempro 250 is still based on load cell strain gauge technology. You might want to start talking to him about magnetic force restoraton scales and truly get to .02 to .001 grains of accuracy in weight. Just thinking outside the box. But still great that you are starting to shed light on how inaccurate a Chargemaster 1500 can be. I saw extreme spreads of .18 grains. When I am loading developing, that is very significant.

 

[thefitter]

Recently I have been working with a friend who is working up loads for his .308 and is at the stage where he is trying to minimize the extreme spread of velocity for loads using Varget, and 175 gr. SMKs.
Toward that end, wanting to give him some sense of the relative importance of a given variance in powder weight, I got out my No. 27 Hodgdon manual and looked the minimum and maximum loads for that combination. Once I had those I subtracted the low values for velocity and charge weight from the high ones and found that for a three grain difference, the difference in velocity was 107 FPS. Dividing that by 3 gave me the change per grain, and dividing that by 10 gave a velocity change per tenth grain of 3.7 FPS. An earlier experiment had showed me that there are approximately four granules of Varget per tenth grain, dividing 3.7 by 4 rounded off to .9 FPS/granule.

Must be nice to be retired.

 

[SWRichmond]

I don't think it would be correct to assume that the pressure curve or the velocity curve are linear for any given grain or kernel of powder. In other words the next kernel has a nonlinear effect, different than the previous kernel. Doing a simple mathematical division is not the right way to answer this question. I also don't think that any consumer chronograph is precise enough to furnish the answer.

 

[Macropod]

I don't think it would be correct to assume that the pressure curve or the velocity curve are linear for any given grain or kernel of powder. In other words the next kernel has a nonlinear effect, different than the previous kernel. Doing a simple mathematical division is not the right way to answer this question. I also don't think that any consumer chronograph is precise enough to furnish the answer.

^^^^ Absolutely. The law of diminishing returns when chasing maximum velocity applies here. The charge/velocity correlation is definitely not linear.

Edit: Very small increments within a particular load range could well be close to linear. This is where it is of relevance to long range work where load consistency does play a role in E.S.

 

[BoydAllen]

Again, and again...I was not particularly looking for some magic number. I was trying to convey some sense of the relative value of controlling a particular variable. In no way did is mean to say that consistency of charge is not important to long range shooting, but rather I was trying to establish what the limits probably are for improvement of ES by improving load weight consistency beyond a certain point. The data that I used came from a manual, not the shooter. I think that the the production of reloading manuals might involve greater expertise, and better equipment than many shooters have. I did not look as small differences in charge weight but rather the velocity differences of charges that differed by three grains. When I have examined the charge weight pressure curves of powders, loads within the recommended range were on the more linear part of the curve. No manufacturer would venture far from that, particularly on the top end, which is where we were, compared to another source, my Sierra manual. I think that we have all probably ventured into that area where a small change in charge caused a large difference in pressure. Given the current product liability situation, I do not see any manual publisher going there with published loads. So often, I see shooters concentrating on some detail in their program when there is something else of much greater importance that they seem to be ignoring. My friend was and is still working on cutting down relatively large ESs and I believe that he needs to look elsewhere for the improvement that he needs for long range work, probably a combination of neck tension and friction between bullet and neck, but we won't know until he does the tests.