Power Charge Load Dev. Question - Noobie
- Thread starter Dixie Reckt
- Start date
Then start testing your loads - powder charge on target. Thats were it count.
Numerous times - the most accurate load is far from having the lowest ES -SD or velocity node stated by someone.
jelenko
Gold $$ Contributor
What is your plan to identify when you have the most accurate load?
A simple powder charge and seating depth matrix at 100 yards can provide a lot of useful information if the equipment and shooter are both up to the task. From there, testing can be expanded.
I think a lot of people end up in constant load development instead of identifying a good charge and seating depth that produces acceptable results on target.
I think a lot of people end up in constant load development instead of identifying a good charge and seating depth that produces acceptable results on target.
I'm going to PO some people here but that isn't my intent. But this concept of flat spots keeps coming up and as an engineer that worked as both a test engineer and combustion engineer during my 43 year career I want someone to explain to me how an increase in energy input doesn't show up as an increase in velocity and then increases again? As part of the explanation it should include an explanation of what changed from one load to another.
As for 3 shot or 5 shot data for examining standard deviation this is paramount to what Hornady covered in Episode 50 of their podcast. Picking 3 or 5 shots, even if that is all that is loaded is equivalent to picking 3 or 5 out of 100 or 1000. It is subject to the laws of probability. Most of the time small sample sizes will underestimate the standard deviation because you draw your sample for an environment where 68% of the sample lie within one standard deviation. Only 32% lie outside one standard deviation. If it isn't obvious this is the most likely cause of the velocity "flat spots". There are also other random factors that can come into play.
Just because the formula's and the software spit out a value doesn't mean that the result is meaningful. The number spit out is ONLY about the the sample, it does not tell you much about the greater population of more loads that are similarly lloaded. It requires additional analysis to begin to expand the sample data to a general population.
Can 3 or 5 shots tell you something? Yes, and many reloaders do use both SD and ES from test. For instance an ES on of 40 on a 3 shot group does probably indicate something is wrong. The probably of a good load sampling to a 40 ES in three or 5 shots is very unlikely. Someone who has sampled large amounts of data have a basis on what to expect and understand the limitations of small sample sizes and single sample tests. They play the odds and assume that if they normally have stand and deviations of 10 then the 25 that they test is likely to indicate something is amiss either with the test or process. There is a chance that the decision is incorrect.
Ultimately the chronograph is a tool that can be used to identify deficiencies in ammunition. Use it as such to help improve you loading but don't let it drive your reloading in search of lower and lower SD or ES.
The graphs below show how a SD of 10 fps affect the overall accuracy of there different shooter/rifle combinations and the importance of evaluating the SD in relation to the shootert/rifle and distance. This particular analysis was for a 150gn SMK @ 2800fps in a 6.5 PRC. Each bullet/cartridge/rifle will be different.
As for 3 shot or 5 shot data for examining standard deviation this is paramount to what Hornady covered in Episode 50 of their podcast. Picking 3 or 5 shots, even if that is all that is loaded is equivalent to picking 3 or 5 out of 100 or 1000. It is subject to the laws of probability. Most of the time small sample sizes will underestimate the standard deviation because you draw your sample for an environment where 68% of the sample lie within one standard deviation. Only 32% lie outside one standard deviation. If it isn't obvious this is the most likely cause of the velocity "flat spots". There are also other random factors that can come into play.
Just because the formula's and the software spit out a value doesn't mean that the result is meaningful. The number spit out is ONLY about the the sample, it does not tell you much about the greater population of more loads that are similarly lloaded. It requires additional analysis to begin to expand the sample data to a general population.
Can 3 or 5 shots tell you something? Yes, and many reloaders do use both SD and ES from test. For instance an ES on of 40 on a 3 shot group does probably indicate something is wrong. The probably of a good load sampling to a 40 ES in three or 5 shots is very unlikely. Someone who has sampled large amounts of data have a basis on what to expect and understand the limitations of small sample sizes and single sample tests. They play the odds and assume that if they normally have stand and deviations of 10 then the 25 that they test is likely to indicate something is amiss either with the test or process. There is a chance that the decision is incorrect.
Ultimately the chronograph is a tool that can be used to identify deficiencies in ammunition. Use it as such to help improve you loading but don't let it drive your reloading in search of lower and lower SD or ES.
The graphs below show how a SD of 10 fps affect the overall accuracy of there different shooter/rifle combinations and the importance of evaluating the SD in relation to the shootert/rifle and distance. This particular analysis was for a 150gn SMK @ 2800fps in a 6.5 PRC. Each bullet/cartridge/rifle will be different.
From what I've seen any testing with a moderately valid sample size basically results in a nearly linear relation between velocity and powder charge.
Hornady has been putting out a ton of info on valid testing and people hate it.
Cortina who used to preach about load dev has also admitted he just shoots the same load.
Erik isn't my favorite shooting references but he often does provide some good guidance. One thing I believe that gets lost in load development discussions is the rifle itself. My opinion, and its based more on discussions with shooters of different disciplines, is that you can't expect a 6lb hunting rifle and a heavy Bench Rest rifle to behave the same in terms of sensitivity to load variations.
As for velocity versus charge the real relationship isn't actually linear but basically proportional to the powder charge/bullet weight)^0.5. For the normal ranges that we work in the difference is negligible.
So I'm not sure I'd trust myself to remember what happened last week much less over a year ago
.I don't see a faint ejector mark on that brass? You would have to point it out to me. I also don't see any primer cratering or flattening either. I'd suggest you use less Neolube and make sure to let it dry before priming/charging the case.
The chrono is useful to ensure you stay in a safe pressure regime. I think how you prep brass, charge the case, and seat the bullet more so influence velocity and its standard deviation.
I assume with a 338 Lapua you are intending on shooting long ranges. The best method to develop a load is a long range ladder test. Shot at 600yds or more. With this method of load development you don't need to concern yourself about velocity (aside from staying within safe pressure). I do use the lab radar when load developing because it is so easy to collect the data and it can be useful in analyzing results when there is a multiple "nodes" to choose from. Ultimately once you have determined your load, then you need the chrono to get velocity. Ultimately you still need consistent velocity but I do believe this is not entirely load dependent, I think this is more controlled by reloading process.
If your load holds waterline at the intended distance then who cares if the velocity SD/ES is tight? The reality is that the velocity data you have collected will only get worse with more replicates. Hornady may be right that if you shoot enough it all normalizes to the same SD/ES. That doesn't mean there isn't a charge or range of charges that won't hold waterline at distance. That is what a long range ladder will find.
Good luck!
Cheers,
Toby
There ya' go. Concise ...
ELR LVR
Silver $$ Contributor
Do you mean to ask, why doesn't the velocity go up linearly and predictably
as the powder charge is increased?
Thats how I read it anyway:
---
There is some things going on in the case that many of us just cannot explain:
1) A specific Powder can act differenty when used in a different case, and can work in a reversely proportional manner
I have seen powder act hotter, or produce higher velocity in one case that is slightly larger,
And then turn around and act SLOWER, with the same charge in a different Smaller case
---
The powder SHOULD HAVE acted hotter or faster in the smaller case
I have to attribute this phenomenon to load density, there being a load density percentage that the powder is most efficient and predictable, when we are at the high efficiency of boiler room for that powder, is where I would suspect the flat spots happen. then act non-linearly when we step outside the optimum efficiency window
---
which is one reason we need to work up loads slowly
rather than taking info straight from the manual.
---
When the physics of powder become more like a hydraulic fluid dynamic, Temp drops inside the case
A change in temp would change the burn characteristics
lets say in the smaller case, the pressure acts as a fluid and temp drops , and so velocity follows.
------------
2) In a .308 once I was loading W-760 trying to find max load and testing at 700 yds
I worked up from 43.0 grns to 45.0 grns
Velocity went up with each incremental change of adding 1/2 grain at a time
I witnessed my bullet impact climbing higher with each shot as I increased the load
until I got to 44.0 grns, where it flattened off
When I got to 45.0 grns, I saw the bullet impact about 1 foot lower than the load of 44.0 grns
Velocity went down once I got to a certain weight/load density.
Putting more powder in past 44.0 grns, decreased velocity
---
It was very strange to me to see that, don't ask me how, I can only speculate that:
The Powder Charge was no longer efficient after a certain point
That Load Density was most efficient at 44.0 grns in that case
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Why would you ignore group size. Many records were set with a big ES. Especially out to 300 yards. With a Low ES and a big group do you throw your data out and start all over? Are you even capable of shooting small groups? What's a velocity node. A flat spot in a plot is just too small of a data set to mean anything.
old_heli_logger
Gold $$ Contributor
Positive Compensation will explain a bunch of this! Here's the video again, but nobody will watch it
You interpreted my question correctly I think. I'll try and comment on what you have posted and if I miss something it's by mistake. Here goes:
There is some things going on in the case that many of us just cannot explain:
1) A specific Powder can act differenty when used in a different case, and can work in a reversely proportional manner
I have seen powder act hotter, or produce higher velocity in one case that is slightly larger,
And then turn around and act SLOWER, with the same charge in a different Smaller case
You are absolutely correct but the impact is understood. It has to do with propagation of the burn front relative to the amount of powder. It also depends on primer ignition propagation. TO your point, a short fat cartridge will behave differently than a long slender cartridge of the same volume and caliber. However, this is not relevant to the supposed change in combustion on a repeatable basis in a single cartridge.
The powder SHOULD HAVE acted hotter or faster in the smaller case
I have to attribute this phenomenon to load density, there being a load density percentage that the powder is most efficient and predictable, when we are at the high efficiency of boiler room for that powder, is where I would suspect the flat spots happen. then act non-linearly when we step outside the optimum efficiency window
---
which is one reason we need to work up loads slowly
rather than taking info straight from the manual.
Load density is tied in with the above. If the powder orientation isn't consistent then the burn will be inconsistent. This typically occurs in partially filled cartridges and is monitored by taking Chrono data with case up and down before loading to demonstrate the sensitivity of the load/cartridge to orientation. Going with recommended case fills of 90+% help minimize this behavior. However, with lessor case fills the results tend to be greater and not repeatable.
2) In a .308 once I was loading W-760 trying to find max load and testing at 700 yds
I worked up from 43.0 grns to 45.0 grns
Velocity went up with each incremental change of adding 1/2 grain at a time
I witnessed my bullet impact climbing higher with each shot as I increased the load
until I got to 44.0 grns, where it flattened off
When I got to 45.0 grns, I saw the bullet impact about 1 foot lower than the load of 44.0 grns
Velocity went down once I got to a certain weight/load density.
Putting more powder in past 44.0 grns, decreased velocity
I have seen this and I can offer a possible explanation. In the case of W-760 the phenomena may be associated with packing (compressing) the powder reducing the frespace between the kernels slowing the burn rate. I believe the same thing happens in extruded powders at higher compressed loads. If this is correct it would be repeatable. However increasing the charge velocity would not recover and continue on the same slope and intercept as the flat spots in question do.
The powder SHOULD HAVE acted hotter or faster in the smaller case
I have to attribute this phenomenon to load density, there being a load density percentage that the powder is most efficient and predictable, when we are at the high efficiency of boiler room for that powder, is where I would suspect the flat spots happen. then act non-linearly when we step outside the optimum efficiency window
---
which is one reason we need to work up loads slowly
rather than taking info straight from the manual.
Again you are talking about different cases. For a flat spot to appear and be repeatable when increasing the Energy input then either the burn rate changes or the energy distribution (losses such as heat and kinetic energy(bullet)) changes. The physics associated with these do not not allow for these to suddenly change for a small increment and then recover to the previous distribution. It's called Conservation of Energy.
When the physics of powder become more like a hydraulic fluid dynamic, Temp drops inside the case
A change in temp would change the burn characteristics
lets say in the smaller case, the pressure acts as a fluid and temp drops , and so velocity follows.
True but irrelevant to the discussion at hand.
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