Experiment for quantifying lot to lot variations of powders

[Michael Courtney]

Hodgdon claims their Extreme line of powders has smaller lot to lot and temperature variations than other brands. We've got some ideas on the back burner to test their claims regarding temperature variation, but we're starting to get much more practical about quantifying the lot to lot variations in velocity for some of their Extreme powders.

The basic idea would be to pick a powder and cartridge, say H4831 in the 25-06. Keep everything else constant (powder charge, lot of brass, lot of bullets, lot of primers, etc.) and shoot 10 shots each with a carefully measured powder charge from a given lot. Repeat for several lots and then compare the average velocities between the lots. (We think we might need to interleave the shots from different lots to eliminate the possibility of changing environmental factors, changing friction with barrel fouling, etc. from confounding the results.) Repeat with different powders and cartridges, H1000 in 6.5x.284; H4350 in 30-06, Varget in .223 etc.

What do you think? Is this a convincing experimental design to detect lot to lot powder variations? What might you suggest we do differently?

 

[jcinsa]

Michael,

when I change powder lots, I load 10 identical rounds with my old lot, and 10 rounds with the new lot.

Record group size, sd and ave velocity.

I just use those figures to decide how similar the lots are, and how they differ.

Then either keep my old load or adjust it.

Works for me.

Regards

John

 

[Rtheurer]

John that is how I do it as well. Only time i dont do that and this happens more than I like is if I run out of powder before i have my new lot.. Ussualy 8 to 16#'s at a time. Ill beworking on another project and go to load ammo say 308 or 6X47 Swiss Match, and find out I have just enough powder left to load for a major match!!! Aw Crap. Too many irons in the fire.

RussT

 

[jo191145]

Fire five foulers first, then 10 shots of each lot Round Robin style as you suggest. That would be enough evidence for me.

 

[fredhorace77]

We suggest that there is no need for you all to do that kind of experiment. There's gonna Always be some small variations From lot to lot in powders . When a powder company produces 1 particular lot that powder is made in a certain condition And environment. These conditions may or may not be identical when the next lot is made. Besides no 1 ever really knows what kind of conditions the powder is exposed 2 during shipping. There are so many external Variables That the company has no control over. Yet so many shooters are so quick To blame the powder company itself. There is always a possibility that the gentleman that you bought the powder from did not Store it properly also. So we feel that the experiment itself would be of no real value

 

[Michael Courtney]

We suggest that there is no need for you all to do that kind of experiment. There's gonna Always be some small variations From lot to lot in powders . When a powder company produces 1 particular lot that powder is made in a certain condition And environment. These conditions may or may not be identical when the next lot is made. Besides no 1 ever really knows what kind of conditions the powder is exposed 2 during shipping. There are so many external Variables That the company has no control over. Yet so many shooters are so quick To blame the powder company itself. There is always a possibility that the gentleman that you bought the powder from did not Store it properly also. So we feel that the experiment itself would be of no real value

Hodgdon sure seemed to put the responsibility on the other powder companies for the lot-to-lot variations Hodgdon measured in their powders. (See: http://www.hodgdon.com/smokeless/extreme/page2.php#top ) They didn't seem to mention the possibility of external variables like the shipping of the lots from other companies and pulling the Hodgdon powders directly from the factory shelves. They also seem to leading the shooter to expect smaller varations in lots of Hodgdon Extreme powders.

And when you say "small variations" are expected lot-to-lot, what do you mean by small? Can shooters really expect variations as small as 8 fps for Hodgdon Extreme powders, as the Hodgdon marketing literature claims, or might variaitons be as large as 50 or 100 fps like Hodgdon claims for some of the competing powders.

 

[jo191145]

Rumor on the bench is, theres a new lot of H-4198 out that requires a full extra grain in the 30BR to get back up to speed.
I did'nt see it personally, just a rumor at the last match.

I'm currently using H-4198 in my 30 begrudgingly. I know the entire BR world has done very well with it.
Still in all my expierience for consistant accuracy over long term I tend to shy away from Hodgen Extremes.
Too many additives in the powder means too many additives in the fouling.
Additives usually accumulate in the bore creating inconsistent fouling conditions.
Inconsistent is never good in the long term.

I'm working on a secret blend for the 30. No idea if it will work but its always fun to try.

 

[K22]

We suggest that there is no need for you all to do that kind of experiment. There's gonna Always be some small variations From lot to lot in powders . When a powder company produces 1 particular lot that powder is made in a certain condition And environment. These conditions may or may not be identical when the next lot is made. Besides no 1 ever really knows what kind of conditions the powder is exposed 2 during shipping. There are so many external Variables That the company has no control over. Yet so many shooters are so quick To blame the powder company itself. There is always a possibility that the gentleman that you bought the powder from did not Store it properly also. So we feel that the experiment itself would be of no real value

Well said! Totally agree - there are too many variables to try and test that way.

Don't the powder manufacturers have quality control parameters (chemistry, density, burn rate, etc.) that they test each lot of powder against to make sure that each lot is within spec?

 

[jo191145]

K-22

I'd have to respectfully disagree. If there are that many variables on such a simple test then everything we do at the bench during load workup is futile.
Might as well just scoop up some powder with a Lee Dipper dump it in and stuff a bullet on top.

There is one variable I try to pay heed too. Probably worth a laugh to most.
Whenever I begin a new jug of powder I like to leave it opened for three days or so to acclimate to the real world.

 

[LHSmith]

K-22

I
There is one variable I try to pay heed too. Probably worth a laugh to most.
Whenever I begin a new jug of powder I like to leave it opened for three days or so to acclimate to the real world.

Thumbs up jo ........except I pour the powder in the measure and let it acclimate ( no top) for a couple hours.........works best when your pre-loading at home where conditions are somewhat constant.

 

[Beau]

Sounds like a waste of time.
Whatever you do, your results will ONLY apply to those lots you tested.

 

[FilippoMo]

Norma claims a lot to lot variation of 10%as industry standard.
Filippo

 

[Michael Courtney]

Norma claims a lot to lot variation of 10%as industry standard.
Filippo

10%, thats 300 fps! I've never seen anything close to a 300 fps change in velocity when going to a new lot of powders. The graph at the Hodgdon site suggests 8 fps for Hodgdon Extreme powders (close to 0.3%) and less than 150 fps for the worst competitor (about 5%). Is threre a documented source for Norma claiming 10% as an industry standard?

10% would likely be a safety issue for reloaders who did not work up loads again from scratch with every new lot of powder.

 

[Michael Courtney]

Sounds like a waste of time.
Whatever you do, your results will ONLY apply to those lots you tested.

It might not show what is typical from a given vendor, but it would show the lot to lot variation that is possible with a given brand of powders. And the more lots that are included in the study, the better idea one gets regarding what other parties would be likely to see.

 

[K22]

K-22

I'd have to respectfully disagree. If there are that many variables on such a simple test then everything we do at the bench during load workup is futile.
Might as well just scoop up some powder with a Lee Dipper dump it in and stuff a bullet on top.

There is one variable I try to pay heed too. Probably worth a laugh to most.
Whenever I begin a new jug of powder I like to leave it opened for three days or so to acclimate to the real world.

No offense taken - I certainly understand the need and value of load develop to ring out the best accuacy for a specific rifle but I think we are talking apples and oranges.

That's why I raised the question about mfg's quality control. I don't know but I would think that the mfg's have developed quality control tests to check each lot of powder to make sure that it's within certain statistical norms.

It just seems to me that using reloads to test powder consistency with so many other variable including loading technique, firearms issues, and variation in other components might lead to questionable conclusions when trying to apply the result to a myriad of other combinations of rifles, twists, loading methods, and components.

 

[Michael Courtney]

That's why I raised the question about mfg's quality control. I don't know but I would think that the mfg's have developed quality control tests to check each lot of powder to make sure that it's within certain statistical norms.

It just seems to me that using reloads to test powder consistency with so many other variable including loading technique, firearms issues, and variation in other components might lead to questionable conclusions when trying to apply the result to a myriad of other combinations of rifles, twists, loading methods, and components.

There is certainly always the tradeoffs between testing the consistency and lot to lot variations of the more fundamental parameters that characterize a powder (heat of explosion, ratio of specific heats, parameters that characterize the burn rate, burn rate vs. pressure, density, grain consistency, etc.) and the more practical issues of pressure and velocity variations in a given application.

Our feeling is that a thorough testing of the more fundamental parameters would be met with skepticism by most shooters who would then ask something more or less, "OK, that's over my head, can you boil that down to the actual velocity variations one might expect in a real application?"

 

[Michael Courtney]

Thank you for your comments and encouragements.

It is much harder to eliminate confounding factors when studying temperature variations than when studying lot to lot variations. The experiment is also harder, since the better design is to maintain the whole system at the test temperature rather than merely conditioning the ammunition. Results can also be sensitive to the choice of temperatures, so one really needs a number of temperature steps across a range rather extremes or extremes and one point in between.

Consider that pressures and velocities can rise as the temperature is lowered in some loads because the propellant grains begin to fracture when hit by the shock wave that originates in the primer detonation. Primers with greater brisance will show this more than primers with less brisance. It is also hard to find a primer whose performance is temperature independent, so that any temperature dependence tests on powders are also testing the primer. We've developed a method for testing primer performance independently of powder. Unfortunately, we do not yet have a method of testing cartridge performance of powders independently of the primers.

Another temperature dependent factor is the bore friction. Different bullets (solid copper, pure lead with a thin jacket, lead allow with a thicker bonded jacket) have different temperature responses for how hard they are to engrave and push through the rifle bore. The stress-strain relationships of brass and barrel steel are also temperature dependent, so the expansion of the chamber region will change with temperature, since the whole action becomes stiffer at colder temperatures.

I agree that Hodgdon's claims regarding temperature insensitivity are suspect. It is notable that Hodgdon reports 25 fps or less variation in the slower Extreme powders. But contrast that with the Mil Spec for the 300 Win Mag load using H1000 which allows for 75 fps variation between the high and low temperatures. And due to the issues mentioned above, the velocity variation at intermediate temperatures might even be larger. And this is with a test method that conditions only the ammo, the rifle is at room temperature.

We lean toward the lot to lot experiment first at a nominal room temperature. Lessons learned on this experiment, as well as feedback we would receive from colleagues and other shooters, would inform a later experiment on temperature variations. Right now we don't have the needed confidence we know how to control the confounding factors in a temperature study.

 

[Michael Courtney]

But at the same time, all the aspects and possibilities that you wrote of to be confounding factors to temperature study, can also all be confounding variables to velocity and pressure results.

I don't think so.

The temperature dependence of primer performance would not be a confounding variable to testing lot to lot powder variations.

The temperature dependence of barrel friction would not be a confounding variable to testing lot to lot powder variations.

The temperature dependence of barrel/action stiffness would not be a confounding variable to testing lot to lot powder variations.

All those variables can be held constant because the temperature is held constant. The only thing changing is the lot of powder between shots. Brass, primers, bullets, friction, etc. are all the same.

 

[K22]

to Michael -

This is one area where Hodgdon's extreme data does not hold water with me at all. While I will do find that their Extreme line of powders are good, and better then many, I have never come close to seeing what they advertise, and quite simply I mark it up to a "marketing gimmick" and to some what as degrading.

Happy Shooting
Donovan Moran

I have always had to adjust my scope settings from sight in's conducted in early March (temperatures in the 40's to 50's) to mid summer (temperatures in the 80's to 90's) for varmint / predator hunting using both Varget and Benchmark powders. Perhaps this is due to changes in air density rather than powder variations, I don't know but I definitely see a difference.

 

[jlow]

Mike,

The key to producing results which are meaningful is to always run what we call in science an internal control. You are right from the stand point that conditions between days will change but what you should always do is if you test say a batch of new powder, you always test a similar size batch of the old – side by side. That is your benchmark and internal control.

If there are external factors affecting the results like primer temp sensitivity, barrel, external temp, etc, they will all affect the original batch and the new batch the same way and the difference between the two is the real difference between the two batches. One has to understand that difference will not manifest itself the same manner and magnitude under different shoot conditions i.e. temps and so the difference has to be qualified with each specific condition. For example, you might not see a difference under freezing conditions but a big difference at hotter temps.

The experiments can be done even better if you shoot the two batches in a round robin manner i.e. alternate shots from the two batches. One thing I would urge you to do though is to carefully time the amount of time the chamber is allowed to cool before you single load your next round and to keep the time that round sits inside the hot chamber. If this is not consistent, the cooking effect of the hot chamber can really confound your results.