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Experiment for quantifying lot to lot variations of powders

 
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  #1  
Old 08-08-2012, 08:08 PM
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Experiment for quantifying lot to lot variations of powders

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?
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Old 08-09-2012, 12:50 PM
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Re: Experiment for quantifying lot to lot variations of powders

RSI's shooting lab, I mean the whole $760 enchilada would probably have the equipment needed to get meaningful results
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Keep in mind the animals we shoot for food and display are not bullet proof. Contrary to popular belief, they bleed and die just like they did a hundred years ago. Being competent with a given rifle is far more important than impressive ballistics and poor shootability. High velocity misses never put a steak in the freezer.

Joe
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Old 08-09-2012, 07:45 PM
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Re: Experiment for quantifying lot to lot variations of powders

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Originally Posted by Joe King View Post
RSI's shooting lab, I mean the whole $760 enchilada would probably have the equipment needed to get meaningful results
We are ballistics professionals. We have strain based systems, including the PressureTraceII. We also have PZT-based pressure measurement systems. Pressure measurements would be more appropriate if the intent of the study was focused on the safety aspects of lot-to-lot variations. We're expecting the average velocity and pressure variations to typically be from 1 to 3% from lot to lot. With careful reloading procedures, lot to lot variations would be unlikely to present safety issues unless they were 5-10%. Also, our experience with the PressureTrace II system suggests that typical accuracy expectations are on the order of 2-3%. Experiments are especially challenging when the measurement uncertainty is about the same size as the expected effect being studied, maybe larger.

The focus of the study is on velocity variations that would be of concern to precision long range shooting. Our LED-based chronographs are capable of 0.1% accuracy when calibrated immediately prior to use. It's hard to see what would be added by pressure measurements only accurate to 2-3%, when the precision of our chronographs allows us to see the variations under study, but the pressure measurements do not.

Chronograph based studies also cost a lot less in terms of prep and are much faster in terms of range time. 50 shots per hour is typical. Pressure-based studies are much more expensive and time consuming, and while some shooters are wowed by the graphs of pressure curves, I'll take reliable velocity data over pressure data of quality that is marginal for the intended purpose.

Don't get me wrong, PressureTrace II is great for its intended purposes, many of which are discussed at the web site:

RSI - PressureTrace

I just don't see what it would add to this study.
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Old 08-10-2012, 10:00 AM
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Re: Experiment for quantifying lot to lot variations of powders

Michael,

I look forward to reading about your results.

A few considerations for this or future experiments...

10 is a pretty small sample.

Perhaps test in parallel with 3 different rifles?

Shoulder fired weapons are said to show different MV depending on individual shooter technique. Perhaps use a lead sled or machine rest?

Certainly you would use cartridges for which the powder is intended. But h4831sc is known to work for many cartridges. Are the results the same regardless of which cartridge (capacity and/or case fill ratio within reason) is tested?

Are the results consistent with minimum, moderate, and maximum loads?

Are the results consistent with light, medium, or heavy bullets?

Does it matter if the load has been optimized for consistent MV?

Isolate temp, atmospheric and other external conditions.

Does chamber pressure track consistent with MV for this experiment?

Are the initial fouling shots statistically different than the rest?

Are all canisters of the same lot # the same?

Are all Hodgdon Extreme powders equally consistent?

Are Hodgdon Extreme powders more consistent than other powders that do or don't make similar claims?

I suppose you need to narrow down the number variables in order to have a manageable experiment. But, my concern would be whether or not your conclusions would be the consistent for all conditions rather than just assuming that to be the case.

-- richard
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Old 08-10-2012, 11:32 AM
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Re: Experiment for quantifying lot to lot variations of powders

Quote:
Originally Posted by Michael Courtney View Post
We are ballistics professionals. We have strain based systems, including the PressureTraceII. We also have PZT-based pressure measurement systems. Pressure measurements would be more appropriate if the intent of the study was focused on the safety aspects of lot-to-lot variations. We're expecting the average velocity and pressure variations to typically be from 1 to 3% from lot to lot. With careful reloading procedures, lot to lot variations would be unlikely to present safety issues unless they were 5-10%. Also, our experience with the PressureTrace II system suggests that typical accuracy expectations are on the order of 2-3%. Experiments are especially challenging when the measurement uncertainty is about the same size as the expected effect being studied, maybe larger.

The focus of the study is on velocity variations that would be of concern to precision long range shooting. Our LED-based chronographs are capable of 0.1% accuracy when calibrated immediately prior to use. It's hard to see what would be added by pressure measurements only accurate to 2-3%, when the precision of our chronographs allows us to see the variations under study, but the pressure measurements do not.

Chronograph based studies also cost a lot less in terms of prep and are much faster in terms of range time. 50 shots per hour is typical. Pressure-based studies are much more expensive and time consuming, and while some shooters are wowed by the graphs of pressure curves, I'll take reliable velocity data over pressure data of quality that is marginal for the intended purpose.

Don't get me wrong, PressureTrace II is great for its intended purposes, many of which are discussed at the web site:

RSI - PressureTrace

I just don't see what it would add to this study.
I take then you can graph out the pressure curve as well. Just seems to me that only looking at muzzle velocity is akin to using blinders. My thinking is generate as much data as you can, not just one type of output. Maybe I read it wrong but once set up doesn't that system stay set up until you take it down? so while your shooting you can get feed back on MV, and a visual of the pressure curve of each shot, thus giving you a much more complete picture of exactly the variation of lot to lot?

For example (only) wouldn't it enable you to identify when the pressure curve starts, ends and the duration. and running that data in conjunction with your chronograph enable you to see just exactly the difference?

Quote:
What do you think? Is this a convincing experimental design to detect lot to lot powder variations? What might you suggest we do differently?
You asked I gave you a suggestion, if you feel the need to get butthurt over it then just disregard my reply pretty simple. Myself if I was going to put out the effort I would want as big of a return on my investment as possible.
__________________
Keep in mind the animals we shoot for food and display are not bullet proof. Contrary to popular belief, they bleed and die just like they did a hundred years ago. Being competent with a given rifle is far more important than impressive ballistics and poor shootability. High velocity misses never put a steak in the freezer.

Joe
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  #6  
Old 08-10-2012, 04:14 PM
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Re: Experiment for quantifying lot to lot variations of powders

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Originally Posted by Joe King View Post
You asked I gave you a suggestion, if you feel the need to get butthurt over it then just disregard my reply pretty simple. Myself if I was going to put out the effort I would want as big of a return on my investment as possible.
That's exactly my point. it's not about any offense. The point is that adding a pressure measurement approximately doubles the cost, time, effort, and expense of the experiment, but I don't see how it doubles the value of the results.

How do the (less accurate) pressure measurements make the determination of velocity variations more convincing? I can see how they might illuminate the underlying causes of any velocity variations that might be observed (pressure variations).

Quote:
Originally Posted by Joe King View Post
I take then you can graph out the pressure curve as well. Just seems to me that only looking at muzzle velocity is akin to using blinders. My thinking is generate as much data as you can, not just one type of output. Maybe I read it wrong but once set up doesn't that system stay set up until you take it down? so while your shooting you can get feed back on MV, and a visual of the pressure curve of each shot, thus giving you a much more complete picture of exactly the variation of lot to lot?
If the extra data added no time or expense, then I would agree, more data is better. But pressure measurements slow data acquisition by a factor of two or three, and the analysis is considerably more involved as well. You're talking about several hundred pressure curves. The system requires attaching a strain gage to a barrel with an adhesive. The calibration procedure is rather involved to ensure accurate results, and the whole procedure needs to be repeated for each rifle barrel in the study for even marginal accuracy.

Quote:
Originally Posted by Joe King View Post
For example (only) wouldn't it enable you to identify when the pressure curve starts, ends and the duration. and running that data in conjunction with your chronograph enable you to see just exactly the difference?
Not really. If the velocity variations are smaller than 1%, how do we expect to see the reasons for it in pressure measurements that are only accurate to 3%? Theoretically, the velocity is proportional to the area under the pressure curve, but the pressure measurements are not accurate enough to correlate with velocity.
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Old 08-10-2012, 04:38 PM
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Re: Experiment for quantifying lot to lot variations of powders

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Originally Posted by Michael Courtney View Post
Hodgdon claims their Extreme line of powders has smaller lot to lot and temperature variations than other brands.
Are you going to prove or debunk this?
If, so you'll need a couple other brands for comparison.
If not, your experiment will only show variances in given lots of one brand -w/resp to those conditions Richard mentioned.
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