Bingo! I like that last sentence but overall well said Boyd!
How important is one kernel of powder?
- Thread starter Fairchaser
- Start date
I can only speak for myself I use OBT /Exit Timing to achieve PC, where rounds from a decent 1k tuned load will impact the same poi despite a slight variance in charge weight so at that point one kernel will not effect the group. I still want my scale to resolve one kernel consistently because that how I got the load and there are several ways to continue to shrink groups, most im still working on' all include wind flags..
Ned Ludd
Silver $$ Contributor
Save yourself the effort and simply do a little math to reach the [correct] conclusion that the effect of a single kernel charge weight variance cannot reliably be registered by most (if not all) chronographs commonly employed by shooters. If the chronograph cannot reliably measure the difference in velocity, by analogy, that difference is effectively meaningless because the whole point of weighing charges precisely is to minimize velocity variance.
As an example below, the average kernel of Varget weighs approximately 0.022 gr. In a small cartridge such as the .223 Rem, the effect of a given charge weight variance would greater than in a much larger cartridge with increased case capacity. For that reason, different values would obviously be obtained with powders having different kernel weights or cartridges of different capacity. However, they won't generally be hugely different. Using actual average velocity values from one of my .223 Rem loads with Varget and 90 VLDs, here is an illustration: 24.3 gr Varget yielded an average velocity of 2763 fps (ES - 17 fps, SD - 8.5 fps).
2763 fps/24.3 gr = 113.7 fps per grain; or ~11.4 fps per 0.1 gr
There are ~4.6 kernels of Varget per 0.1 gr, so:
(11.4 fps/0.1 gr) X (0.1 gr/4.6 kernels) = ~2.5 fps predicted velocity change per kernel Varget
First, it would be a stretch to think that most chronographs are accurate in the 1 to 2 fps range. If any are, it would be at the extreme limit of their accuracy/precision. Further, the 2.5 fps per kernel Varget theoretical velocity estimate is well below even the best ES values that shooters would routinely obtain with loads having excellent ES values, which I would classify as being somewhere in the ~4 to 7 fps range. Such low ES values are not easy to routinely obtain, even for those already weighing powder to +/- half a kernel, suggesting that the velocity variance (ES) at this level is almost certainly due to other factor(s) besides charge weight variance.
Nonetheless, sources of error can be cumulative, and weighing powder to +/- one kernel (or slightly less) is not really very difficult, so there are many that do weigh powder to that level of precision as a means to effectively remove charge weight variance as a limiting source of error. Having said that, I wouldn't really recommend anyone go out and start testing charge weights that differ by a single kernel in weight just to demonstrate a principle that can be effectively estimated far more easily. Even if someone is really masochistic enough to do this experiment, it is worth noting that having a properly calibrated analytical balance of sufficient precision (i.e. 0.0001g readability, ~0.0002g precision) would be essential before undertaking such an exercise. Don't try it using a Chargemaster.
CharlieNC
Gold $$ Contributor
Save yourself the effort and simply do a little math to reach the [correct] conclusion that the effect of a single kernel charge weight variance cannot reliably be registered by most (if not all) chronographs commonly employed by shooters. If the chronograph cannot reliably measure the difference in velocity, by analogy, that difference is effectively meaningless because the whole point of weighing charges precisely is to minimize velocity variance.
As an example below, the average kernel of Varget weighs approximately 0.022 gr. In a small cartridge such as the .223 Rem, the effect of a given charge weight variance would greater than in a much larger cartridge with increased case capacity. For that reason, different values would obviously be obtained with powders having different kernel weights or cartridges of different capacity. However, they won't generally be hugely different. Using actual average velocity values from one of my .223 Rem loads with Varget and 90 VLDs, here is an illustration: 24.3 gr Varget yielded an average velocity of 2763 fps (ES - 17 fps, SD - 8.5 fps).
2763 fps/24.3 gr = 113.7 fps per grain; or ~11.4 fps per 0.1 gr
There are ~4.6 kernels of Varget per 0.1 gr, so:
(11.4 fps/0.1 gr) X (0.1 gr/4.6 kernels) = ~2.5 fps predicted velocity change per kernel Varget
First, it would be a stretch to think that most chronographs are accurate in the 1 to 2 fps range. If any are, it would be at the extreme limit of their accuracy/precision. Further, the 2.5 fps per kernel Varget theoretical velocity estimate is well below even the best ES values that shooters would routinely obtain with loads having excellent ES values, which I would classify as being somewhere in the ~4 to 7 fps range. Such low ES values are not easy to routinely obtain, even for those already weighing powder to +/- half a kernel, suggesting that the velocity variance (ES) at this level is almost certainly due to other factor(s) besides charge weight variance.
Nonetheless, sources of error can be cumulative, and weighing powder to +/- one kernel (or slightly less) is not really very difficult, so there are many that do weigh powder to that level of precision as a means to effectively remove charge weight variance as a limiting source of error. Having said that, I wouldn't really recommend anyone go out and start testing charge weights that differ by a single kernel in weight just to demonstrate a principle that can be effectively estimated far more easily. Even if someone is really masochistic enough to do this experiment, it is worth noting that having a properly calibrated analytical balance of sufficient precision (i.e. 0.0001g readability, ~0.0002g precision) would be essential before undertaking such an exercise. Don't try it using a Chargemaster.
I would not do this myself because I consider one kernel inconsequential. But if the OP really wants to know the target trumps theory.
dcali
Bullet Maker
It's a simple matter of one kernel being a bigger percentage of the charge weight in a small cartridge, so it will have a bigger impact on velocity.Thinking out loud....
1 kernal of powder = potential energy. The same amount of potential energy, regardless of how many other kernels are with it. If , upon detonation, 1 kernal of powder = 1 joule of energy (for lack of a better unit of energy,) then 250 kernels of powder = 250 joules.
As such I'm not understanding how "the importance of a single granule of powder depends on the total charge weight".... as its a linear relationship, not exponential.
Of course, there's alot of things I don't understand.
A cartridge that shoots a 50 grain bullet with 10 grains of powder will achieve the same velocity as a cartridge that shoots a 500 grain bullet with 100 grains of powder. (all else equal).
But he velocity increase of the first cartridge when using 10.1 grains will be more than the second using 100.1.
energy = 1/2 * mass * velocity^2
so ...
energy/mass = 1/2 * velocity^2
Note that if the energy/mass ratio of two cartridges is the same, then the velocity must also be equal. If you then add one kernel to each, the energy to mass ratio between the two cartidges changes. You'd have to up the powder by the same *percentage* to keep them the same, which is why the smaller cartrige is more sensitive to powder charge weight.
garandman
Bolt Gun Bodacious
@damoncali ... that makes sense. Esp. In light charges like 22rf or sub 9mm.
The way I read your analysis you're talking about percent increase of power of one kernel of powder... especially for very light charges. The percentage increase of those lighter charges would be significant.
What I'm talking about is incremental increase in power of heavier charges of 30 40 50 grains. The incremental Power from kernel 256 is exactly the same as the incremental power added by kernel 257.
The way I read your analysis you're talking about percent increase of power of one kernel of powder... especially for very light charges. The percentage increase of those lighter charges would be significant.
What I'm talking about is incremental increase in power of heavier charges of 30 40 50 grains. The incremental Power from kernel 256 is exactly the same as the incremental power added by kernel 257.
dcali
Bullet Maker
Right. The energy increase of each kernel is identical regardless of powder charge. But the percentage increase in total energy is more for kernel 256 than it is for kernel 257. The general trend still holds, it's just not as noticeable. The larger the charge is, the less it matters how many kernels off you are.
This is why .223s are generally considered to be more finicky than .308s. The .308 is roughly twice as much powder, shooting roughly twice as much bullet. Each additional kernel matters more to the .223 than the .308, even though they contain the same amount of energy. Since the smaller .223 cartridge is impacted more, you need to be a little more careful about how tight your charge weights are to achieve the same velocity consistency as a .308.
BoydAllen
Gold $$ Contributor
I think that you might want to think a bit more. Think in terms of what percentage of the total charge a granule would be for a .22 hornet, and for a big magnum.Thinking out loud....
1 kernal of powder = potential energy. The same amount of potential energy, regardless of how many other kernels are with it. If , upon detonation, 1 kernal of powder = 1 joule of energy (for lack of a better unit of energy,) then 250 kernels of powder = 250 joules.
As such I'm not understanding how "the importance of a single granule of powder depends on the total charge weight".... as its a linear relationship, not exponential.
Of course, there's alot of things I don't understand.
garandman
Bolt Gun Bodacious
Already addressed that.... percentage increase vs. Incremental increase.
Incremental increase is exactly the same from 21 to 22 kernels as it is from 310 to 311 kernels.
That applies to SHORT range BR, not long range BR.
Isn't everybody assuming EVERY kernel is mixed EXACTLY the same? Can anyone confirm this? As long as we are nitpicking AND just stirring the pot... I have no idea btw.
A single kernel of Varget weighs .02gr, so you’re both equidistant from the nominal of 5 kernels, in opposite directions.
A well tuned load may have say a 20 fps velocity node. In a typical 6 BRA 1000 yd BR rifle that might be between 2920-2940 fps where we get positive compensation and all that. So if one kernel equaled 2 fps, then a 10 kernel variance shouldn't be a problem, right?
Wrong. There is velocity variation with every shot. Nothing stays the same between shots. The barrel has more fouling, the barrel temp is different, the shooter squeezes the trigger slightly differently. Each case springs back a little differently. The outside air temp, barometric pressure, humidity, and wind are all constantly changing as well. We don't know how many fps all of that contributes to the bullet's velocity along its path.
So we don't know how much of our 20 fps is eaten up with the changes we can't control. So not makes sense to load as consistently as we can to minimize the velocity changes that we can control. Thus charging powder as consistently as possible, and within 1 kernel is very possible with the A&D FX-120i and Sartorius Entris, makes sense for
LR BR applications. The less variation we start with, the less we will end up with.
Not sure this level of precision is needed for shooting disciplines other than LR BR and ELR. Certainly not with hunting or casual target rifles. However, it's not that hard to get that level of consistency in loading nowadays with the equipment we have available to us.
Wrong. There is velocity variation with every shot. Nothing stays the same between shots. The barrel has more fouling, the barrel temp is different, the shooter squeezes the trigger slightly differently. Each case springs back a little differently. The outside air temp, barometric pressure, humidity, and wind are all constantly changing as well. We don't know how many fps all of that contributes to the bullet's velocity along its path.
So we don't know how much of our 20 fps is eaten up with the changes we can't control. So not makes sense to load as consistently as we can to minimize the velocity changes that we can control. Thus charging powder as consistently as possible, and within 1 kernel is very possible with the A&D FX-120i and Sartorius Entris, makes sense for
LR BR applications. The less variation we start with, the less we will end up with.
Not sure this level of precision is needed for shooting disciplines other than LR BR and ELR. Certainly not with hunting or casual target rifles. However, it's not that hard to get that level of consistency in loading nowadays with the equipment we have available to us.
BoydAllen
Gold $$ Contributor
In terms of pressure, internal and external ballistics that is absolutely not true.
Ned Ludd
Silver $$ Contributor
To a large extent, it depends on the powder. Some powders have more uniform kernels than others, so for those it is fairly reasonable to use the average weight of a kernel for making rough estimates. However, some powders are far less uniform in size/weight. I recently started working up some loads with AA4064. The kernels range in size from very short, to medium, to very long. The corresponding weights for short, medium, and long kernels range from ~0.025 gr, to ~0.040 gr, to almost .060 gr. With a powder such as that, you could probably use the "average" weight of a kernel for crude estimates, but the number of kernels of each size is not uniform, so any estimate would be very coarse at best.
Nonetheless, if all you're trying to do is come up with a crude estimate of approximately how much a single kernel would change velocity, such an estimate is going to be more than close enough to illustrate the principle that a single kernel of powder won't change the properties of a given load in any measurable or definable way. The whole point of the exercise is not to accurately define the average weight of a kernel of any given powder, but simply to come up with an estimate of how many kernels might be in a given charge weight to divide the average velocity by and generate some working value for how many fps velocity a single kernel might be worth. Strictly speaking, using some defined weight values rather than kernels would be better for the exact reason you mention, but it doesn't really matter. You could also measure velocity and assess group size for loads to which you've added an "extra" one, two, three kernels, etc., but that's a total snipe hunt, so don't waste your time. A single kernel of powder is never going to be the limiting source of error in terms of velocity variance. As I have mentioned a couple times earlier, the main reasons people weigh powder to +/- one kernel are because it isn't that much more effort to do so with the right equipment, and you're then effectively removing charge weight variance as a potential source of velocity variance.
In the reloading process, there are a number of things people interested in achieving the best possible precision will often take down to a level well beyond what is minimally necessary, but again, the idea is to effectively prevent some variable from ever becoming a limiting source of error by making it much smaller than it absolutely has to be. The real choice involved in using such an approach is to decide how much extra time/effort doing so may cost. Only the individual can decide whether taking any given step in the reloading process to an extreme of precision is worth the effort. Examples of steps that I personally carry out that others may or may not consider worth the effort include weighing powder to +/- one kernel (or less), weight-sorting brass to improve case volume consistency, and length-sorting/pointing bullets. Each of those steps does take time, but not huge amounts of time in the grand scheme of things, so I am willing to do them and I have been very satisfied with the results. In contrast, I could sort cases for volume far more accurately by determining water volume. But that process would require a stupid amount of effort for the large number of cases I go through as an F-Class shooter, so I just sort them by weight and call it a day.
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dcali
Bullet Maker
I believe he means the same in energy content, which is true, and also the reason that what you're saying is true...
dcali
Bullet Maker
This is reaaallllyyy splitting hairs, but...
Usually, that's the goal for powder manufacturers. The oversimplified way to put it is that the burn rate is largely a matter of kernel geometry - powder burns at a rate that's proportional to its surface area, which changes as it burns. So if you want every kernel to burn at the same rate, they all need to be the same size and shape to start with. Pragmatically, some variation won't be noticed. With a powder like Varget, which is fairly coarse, you can visibly see without measuring that every kernel is *not* the same. But they're close enough for this conversation.
That said, there's no reason it has to be that way - I'm not sure why you would, but intentionally mixing sizes would certainly be possible. I guess you could manipulate the pressure curve this way. And of course, manufacturing tolerances are what they are. And as Ned says above - some powders are more consistent than others (the annoyingly long sticks like IMR 4064 are going to vary more than fine, short extruded powders).
garandman
Bolt Gun Bodacious
That's what I'm saying. Ever single kernel of powder had the same INCREMENTAL potential energy as every other kernel of powder whether it's #1 or #:1000.
Obviously, kernel # 1 is a 100% increase from 0 kernels, but only a 0.1%:increase from 1,000 kernels. That's a different analysis of PERCENTAGE increase.
Alex Wheeler
Site $$ Sponsor
I lost most of my pictures when my computer went down but heres a couple 1000yd tests I found. I test with three shot groups all fired quickly, so I would run all 9 shots fast to beat conditions. Each of these are .1gn. apart in powder charge. .1 can make a big poi change at 1k, it looks bigger the smaller the rifle is shooting. A great barrel will sometimes give you a .1 either way at 1k, but an average barrel probably wont. 
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