GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on June 15, 2018, 07:38:08 PM
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I have recently been asked to join the crew at Hard Air Magazine as Technical Editor.... I will be writing monthly articles, and the first is now online here....
https://hardairmagazine.com/ham-columns/airgun-technical/ham-airgun-technical-how-pcp-airguns-work/
The plan is to write my articles as a short series with a common theme or starting point.... I hope you enjoy them.... I will admit to a selfish motive, the compensation will eventually go towards purchase of a LabRadar for my retirement enjoyment....
Bob
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Congratulations Mr. Bob
I have enjoyed your technical know-how here on GTA and very much look forward to reading your articles.
Good luck with this endeavor sir.
Ray
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Bob, that is great, congratulations. I just read your article and learned a few things.
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Look forward to reading more of your articles , it was easy to follow with clear illustrations
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Great article Bob. And congrats on the new gig.
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Looking great there Bob !!!
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Congrats on the new “job” Bob. Looking forward to reading the articles.
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Congratulations and well deserved ! I look to many of your posts here at GTA for guidance and direction!
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Congrats! I look forward to more of your articles.
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Nice writing there Bob , clear concise and easy for those not familiar to air gun lingo to understand!
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Good article Bob!
Thanks
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Congratulations! Some of us have been wishing for some time that your work would be compiled in a printed format. Well, here we go getting closer to that! Good article, by the way. Also passed on the link to others.
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Congratulations Bob,
Looks like the start of a great series of articles
Thanks
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They couldn't have found a better guy!!!
The dopes at crosman should have hired you as a consultant years ago. Their loss.
Compensation.... WOO-HOO
Steve
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Hey Bob,
Good for you!
Good for the Air gun folks that want to learn!
My Best to You
-Cindi
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Congrats Bob...
I read your postings for 2 reasons...
1. To learn.
2. When I want to know how dumb I am.
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Two thumbs up my friend. :D
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A win all 'round!
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Nice job! Well written! :D
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Bob - It's good to see that your horizons are expanding. You're certainly a great asset to the technical side of airgunning and you've designed and executed many excellent projects. Keep up the fine work!
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The second article in this series about PCPs is now online....
https://hardairmagazine.com/ham-columns/how-to-obtain-the-maximum-power-from-a-pcp-air-rifle/
Enjoy !!!
Bob
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Thanks, Bob! Indeed I did. :D
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Article #3 in the PCP series is now online....
https://hardairmagazine.com/ham-columns/understanding-pcp-airgun-power-factors/
Bob
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Article #4 is now available....
https://hardairmagazine.com/ham-columns/the-effect-of-port-sizes-on-pcp-airgun-power/
Bob
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Bob, thank you for writing these. I can appreciate the effort that goes in, especially when there is a lot of test data involved, like the Disco port size effect series you included in this 4th article.
Thanks again
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Great article Bob. Clear and easy to understand, even for me.
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Very timely article, as I am trying to understand how these many factors work together.
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Another great article! Thanks Bob. :D
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Bob, Since these are outside of GTA, is there a place for those of us coming up to speed to ask questions?
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Bob as always your constant testing and reviewing of test results has contributed a great deal to the overall performance of Air Rifles over the years. Thank you for all you continue to contribute to our awesome hobby
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Part 5 of my series on PCPs is now online at HAM....
https://hardairmagazine.com/ham-columns/using-hammer-strike-to-control-pcp-power/
Bob
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Bob
Thank you,
Now all this info is starting to fall in place, finally.
Looking for the SSG part.
Tia,
Don
ps, I am saving all this info...........
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Great stuff! I have been working on my PCPs for the last couple years and you have already helped greatly. Just reread your articles and had several “duh” moments. Thanks again!
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Part 6 of my series of articles on PCPs is now online at HAM....
https://hardairmagazine.com/ham-columns/conserving-air-in-pcps-hammer-bounce-and-the-ssg/
Bob
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Bob, great write up, thanks
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Excellent write up Bob. The entire series has been very informative
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Well written.... I even understood it.
Thanks Bob.
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Part 7 of my articles on PCPs is now online at HAM.... https://hardairmagazine.com/ham-columns/balanced-valves-for-pcp-airguns-theyre-here-today/
This month I share how Balanced Valves work....
Bob
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Those articles posted here already?
:)
If not, they should be.
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Those articles posted here already?
:)
If not, they should be.
Yes they should be posted to the GTA Library if possible
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Not in precisely the form they are on HAM.... It wouldn't be fair to copy/paste my threads over there and then get paid (nominally) for them.... HAM hold the copyright on the articles posted there, of course.... That is why I have linked to them here.... There are, after all, free to view....
The information I have posted here, over the years, has all the same content (and more)…. just not organized in the same way....
Bob
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Maybe there could be a spot in the library for a list of links to all of your articles. Or a pinned thread at the top of your forum section with all the links.
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That is the purpose of this thread.... Links to all my HAM articles are here....
Bob
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Article 8 in my series on PCPs is now online.... https://hardairmagazine.com/ham-columns/bobs-guide-to-tuning-unregulated-pcps/
This one is on Tuning Unregulated PCPs....
Bob
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Article #9 on PCPs is now online at HAM.... https://hardairmagazine.com/ham-columns/introduction-to-the-pcp-regulator-dont-ignore-the-plenum/
This time it is on setting up regulated PCPs....
Bob
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Part 10 of my series on PCPs is now online.... https://hardairmagazine.com/ham-columns/tuning-regulated-pcp-airguns/
Bob
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Part 11 of my series of articles, and the last one on PCPs is online....
https://hardairmagazine.com/ham-columns/pcp-efficiency-what-is-it-what-changes-it/
Next month I begin a series on Ballistics, Internal, External and Terminal....
Bob
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Bob. great article as always.
Towards the end there is a line "Insert “Dual Power Hammer” here." looks like a graphic didn't make it in.
Thanks for your work.
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Yeah, I know.... I sent it but they didn't put it in.... I let them know but they are on holidays....
We'll get that inserted.... eventually....
Bob
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Wow didn't notice the error I mentally inserted the image ;)
I see Bob will be going ballistic next :o
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My first article on Ballistics is now online at HAM.... https://hardairmagazine.com/ham-columns/pcp-airgun-internal-ballistics/
This covers the Internal Ballistics of PCPs, so is basically a transition from the PCP Series to the Ballistics Series....
Bob
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Bob,
Nice write up as always. Is there a description somewhere of the model you used and what assumptions it makes.
Thank you again
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Lloyd's Internal Ballistics Spreadsheet uses Newtonian Mechanics (F=ma) as the primary calculation.... where the force is the pressure in the barrel times the base area of the pellet/bullet.... The mass starts out as the mass of the projectile, but as air is added to the barrel, that is included in the mass to be accelerated.... That (declining) force is applied to the (increasing) mass until the pellet/bullet leaves the muzzle.... so the acceleration is constantly decreasing during the shot....
Other correction factors (losses) included in the calculation are the starting and sliding resistance of the pellet (guesstimated), the pressure drop due to the (wasted) transfer port volume, the volume of the reservoir or plenum (the smaller it is, the faster the pressure drops during the shot), and the mass of the gas used (eg. Helium is lighter than air, CO2 is heavier)…. Other input variables are the valve dwell and an "efficiency factor" which looks after other losses such as port size, etc.etc.etc…. The spreadsheet makes a calculation for every 0.00002 sec. until the projectile leaves the muzzle.... and so "integrates" the result (each increment uses the end point of the previous one for its starting conditions)….
It turns out that for the calculator to match real world results, there is only one combination of dwell and the efficiency factor that will produce both the test velocity and the volume of air used in the empirical data you are trying to match.... While there are undoubtedly things not accounted for, the model "works", and can be used to predict quite closely what happens when you change different inputs, such as pressure, caliber, pellet weight, etc.etc.etc…. Simply put, it is the "best" tool we currently have to model PCP Internal Ballistics (also CO2 guns and pumpers)….
Bob
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Bob, thank you for the description.
It looks like from the charts that the pellet starts with full pressure behind it. Is that assumed or is the starting friction input at high value to allow the pressure rise in the breach to complete its rise time?
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When the valve opens even a few thou, the transfer port volume fills with air at a very high speed, probably close to the 1650 fps molecular velocity, ie it takes about .05 mSec for the air molecules to reach the base of the pellet, but at that instant the only volume of air that has flowed through the valve is enough to fill that volume.... With such high pressure available in such a short period of time, the pellet then starts a very rapid acceleration.... The starting force is only a few lbs. for a pellet, somewhat more for a bullet, and a lot more if the bullet is too tight a fit in the bore....
There is a small initial pressure drop to fill the ports, and then a larger, more gradual drop as the pellet moves down the barrel during the "valve open" phase.... Once the valve shuts, the pressure starts a much more rapid decline as the air between the valve and pellet then expands as it accelerates the pellet down the bore....
It there is a small error in the assumptions, that is compensated for by the overall "efficiency" factor used to balance the spreadsheet and make it agree with your test results.... Once that "fudge factor" is known for a given gun, you can change pellet weight, pressure, valve dwell, even barrel length or caliber, and get a close estimate of what to expect....
Bob
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I was thinking back to the breech pressure transient test data that George presented in his long testing thread in the engineering gate. There the pressure rise took about .5 msec and never reached the full pressure you would expect for CO2. The pellet started at about .2 msec and 200 psi. Granted the Disco is running at higher pressure but I wonder how that time affects the results. Perhaps it just looks like additional dead volume.
Thanks for the explanation
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There are definitely "time lags" not taken into account in Lloyd's spreadsheet.... how long it takes between the hammer strike and the valve actually cracking as the poppet head decompresses.... the time it takes for the random molecular motion in the valve to "organize" and flow into the ports.... when the pellet actually sees enough pressure to start moving.... and probably some others.... Think of the start of Lloyd's graph as the instant the pellet start to move and it might be easier to understand.... ie you have to add all the "lag times" to the "valve open dwell" to get the "total dwell" from hammer strike to valve close.... All those lag times are to the left of "zero"....
No model is perfect, and when somebody comes up with a better one, I'll only be too happy to use it.... Lloyd has been working on his for many years, ever since I "met" him in fact, and probably before that.... We still don't know if the expansion is closer to Adiabatic (as theory says) or Isothermal (which it isn't as the exhaust plume of a PCP definitely cools)…. I am 99.9% sure it isn't purely Adiabatic, because that would put a maximum on the efficiency (eg. ~ 2.34 FPE/CI at 3000 psi) which we are closely approaching and sometimes exceeding.... Again, in practical terms, all that changes if you use Adiabatic, Isothermal, or something in between (Lloyd's spreadsheet can do that, and separately for the valve open and valve closed stages)…. is that you end up using a different combination of valve dwell and efficiency to make the spreadsheet agree with empirical data.... The cool thing is that regardless of the assumptions and inputs, there is only ONE combination of those two inputs that will work to match your data....
Bob
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Thank you Bob.
I'm not questioning the validity or the effort that you and Lloyd put into building the model. I am always interested in how modeling compares to test data. It usually helps me understand what is going on. I understood the chart to be from pellet start. Is there a chart of that shot cycle plotted against time?
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There is one available in the spreadsheet, but I have never used it.... I am pretty sure this is the same inputs as I used to generate the first chart in the HAM article....
Bob
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External Ballistics of Pellets at HAM....
https://hardairmagazine.com/ham-columns/the-external-ballistics-of-diabolo-pellets/
Bob
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Thanks for all your information Bob.
Thats why I joined GTA. For one, to search the wealth of information contained here. Nice to see this information is easily accessible on HAM.
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Article #14.... The External Ballistics of Slugs in Airguns…. is now online at HAM....
https://hardairmagazine.com/ham-columns/the-external-ballistics-of-slugs-in-airguns/
Bob
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Article #15 is now online at HAM.... https://hardairmagazine.com/ham-columns/wind-drift-for-airguns-its-important-where-the-wind-is/
Bob
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Article #15 is now online at HAM.... https://hardairmagazine.com/ham-columns/wind-drift-for-airguns-its-important-where-the-wind-is/ (https://hardairmagazine.com/ham-columns/wind-drift-for-airguns-its-important-where-the-wind-is/)
Bob
Thanks Bob! Always good articles from you.
Thanks again!
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Good stuff Bob.
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Bob, if I may, I have a question concerning Article #15. A friend is shooting in EBR. Last year he set up a Windicator flag at 50 yards, after reading your article he will move it back to 25 yards for this years competition. My question is, in your opinion, what would be the ideal distance to set his Windicator flag? Much thanks.
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"Best" would be several, near the bench, 25, 50 and 75 yards.... so that you can study the way the wind changes over the course, and what happens in gusts.... However, the strength and direction of the wind nearest the muzzle will have the greatest influence on drift and vertical "jump".... which is the subject of my next article.... If I had to choose one distance for a flag, about 1/4 of the way to the target would be my preference....
Bob
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As a former across the course and 1000 yard shooter these have been great to read. I’m still too new to pellets and 100 yards but I like flags over the course if available.
Never too old to think and learn. Thanks for the knowledge.
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Article #14.... The External Ballistics of Slugs in Airguns…. is now online at HAM....
https://hardairmagazine.com/ham-columns/the-external-ballistics-of-slugs-in-airguns/
Bob
Good Stuff Bob,
I'm glad to see someone has been sharp enough to publish your airgun knowledge for all to see.
Great graphs to demonstrate your findings ;). Hopefully "Hard Air Magazine" will be wise enough to publish a book with a collection of your articles ..... which I will eagerly buy 8).
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Once a couple of years worth of articles is collected.... we are discussing that possibility.... shhhhhhhhhhhhhh…. ;)
Bob
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Once a couple of years worth of articles is collected.... we are discussing that possibility.... shhhhhhhhhhhhhh…. ;)
Bob
Good, that'll ensure a steady flow new Toys are be delivered to Coalmont 8).
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The next article in my series on External Ballistics is now online at HAM.... Article #16 deals with Vertical Deflection in a Crosswind....
https://hardairmagazine.com/ham-columns/vertical-deflection-for-pellets-in-crosswind/
Bob
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Article #17, on Pellet and Slug Stability, is now online at HAM....
https://hardairmagazine.com/ham-columns/pellet-and-slug-stability/
Bob
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Hopefully "Hard Air Magazine" will be wise enough to publish a book with a collection of your articles ..... which I will eagerly buy 8).
I'll buy THREE.
Nothing like that book exists yet.
No-one I know has been as helpful as Bob in the area of AG ballistics and many other topics.
He's been doing the double work of
(1) figuring stuff out, AND
(2) publishing it in an understandable manner.
THANK YOU, Bob, for serving us!! 😊
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Hard Air Magazine has now added an Index to my Technical Posts.... This is the article showing how to find the Index....
https://hardairmagazine.com/ham-columns/now-its-easy-to-find-bob-sternes-airgun-technical-posts/
Here is a direct link to all the articles.... Now you will be able to find all my online articles at one place....
https://hardairmagazine.com/tag/airgun-technical/
Bob
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The 18th article I have written for HAM is now online at:
https://hardairmagazine.com/ham-columns/pellet-twist-rate-and-stability/
Bob
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This month and next my articles at HAM concentrate on the Drag and Ballistics Coefficients.... Number 19 is now online....
https://hardairmagazine.com/ham-columns/drag-coefficient-and-ballistics-coefficient-explained/
I hope you enjoy this pair of articles.... Merry Christmas and a Happy New Year to you all....
Bob
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This month and next my articles at HAM concentrate on the Drag and Ballistics Coefficients.... Number 19 is now online....
https://hardairmagazine.com/ham-columns/drag-coefficient-and-ballistics-coefficient-explained/ (https://hardairmagazine.com/ham-columns/drag-coefficient-and-ballistics-coefficient-explained/)
I hope you enjoy this pair of articles.... Merry Christmas and a Happy New Year to you all....
Bob
Thanks Bob!
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Article #20 at HAM is now online....
https://hardairmagazine.com/ham-columns/the-future-of-airgun-ballistics-coefficients/
Bob
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Thanks Bob!
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That Lab Radar sure does open up a whole new world for your research, and the airgunning community as a whole, to quote Rick Eutsler, It is a great time to be an airgunner 8)
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The next article, #21, which I have written for Hard Air Magazine is online at....
https://hardairmagazine.com/ham-columns/how-important-is-extreme-spread-to-accuracy/
Is ES important?.... Yes, but other factors are even more important!.... Enjoy !!!
Bob
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The next article, #21, which I have written for Hard Air Magazine is online at....
https://hardairmagazine.com/ham-columns/how-important-is-extreme-spread-to-accuracy/
Is ES important?.... Yes, but other factors are even more important!.... Enjoy !!!
Bob
Good read, and I chart things similarly when evaluating precision/accuracy, EXCEPT - I usually use SD (Standard Deviation) rather than ES (Extreme Spread).
ES is good for determining the number of acceptable shots from an unregulated PCP, but for groups of shots from a piston gun or regulated PCP, SD is a better measure.
With ES, the two most outlier shots determine the value. SD factors in all shot equally.
It's nice to hit 100% in a string of difficult shots, but realistically, I don't expect too. The SD gives me the probability of the miss. Over time that's what matters for long term success in target shooting. Not hitting them all, but knowing that you can hit more than the next guy.
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The next article, #21, which I have written for Hard Air Magazine is online at....
https://hardairmagazine.com/ham-columns/how-important-is-extreme-spread-to-accuracy/ (https://hardairmagazine.com/ham-columns/how-important-is-extreme-spread-to-accuracy/)
Is ES important?.... Yes, but other factors are even more important!.... Enjoy !!!
Bob
Thanks Bob!
Most of my shots are are ~25 yards +/- 5~10 yards, but I do shoot the occassional shot at ~55 yards.
It is very interesting how much MORE estimated range mistakes have an affect on POI than ES at longer ranges. Not to mention the wind...
(https://hardairmagazine.com/wp-content/uploads/2020/02/HAM-4-Trajectory-Errors.jpg)
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Bob,
That article has been the biggest eye opener for me — HUGELY IMPORTANT. ❌
Thank YOU for sharing all your profound insights and intelligent analyses with us!! 👍🏼 😊
Scotchmo,
would you briefly share how to calculate SD and what it really means? 😊
Matthias
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Bob,
That article has been the biggest eye opener for me — HUGELY IMPORTANT. ❌
Thank YOU for sharing all your profound insights and intelligent analyses with us!! 👍🏼 😊
Scotchmo,
would you briefly share how to calculate SD and what it really means? 😊
Matthias
ES only considers the highest and lowest. SD requires all the shots, so it's a more involved calculation. I usually just enter all the shots into a calculator that has an SD function. Here is one:
https://www.calculator.net/standard-deviation-calculator.html (https://www.calculator.net/standard-deviation-calculator.html)
That page also shows the formula and how to do it manually if you want to do that.
With ES, it's YES or NO on whether it's good enough to hit a specific size target. It's kind of binary.
SD tells us the probability of a shot being inside or outside of any spread. Typically a bell curve. It's more analogue.
If we use ES:
it's hit (YES) or miss (NO)
If we use SD:
+/- 1 SD gives us 68.3% chance inside
+/- 2 SD gives us 95.4% chance inside
+/- 3 SD gives us 99.7% chance inside
+/- 4 SD gives us 99.99% chance inside
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Would it not be the lower SD has the higher probability? The higher the SD the lesser probability?
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Would it not be the lower SD has the higher probability? The higher the SD the lesser probability?
I was showing multiples of the SD, not the value of the SD. Higher multiple of SD have the greater chance of occurring.
A random instance has a 68.3% chance of lying within 1xSD. And 95.4% chance of lying within 2xSD.
You want the fps SD value of your gun to be as low as possible.
If you have a gun that shoots 900fps and SD(value)=9fps, that means:
+/- 1xSD gives 68.3% chance of 891-909fps
+/- 2xSD gives 95.4% chance of 882-918fps
If the target is so small that only a 1xSD variation is acceptable, then you have only a 68.3% chance of hitting it, even if you make a good shot.
If the target bullseye is big enough so that a 2xSD variation is acceptable, then you have a 95.4% chance of hitting it, assuming you make a good shot.
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Scott,
that was pure CRISTAL!! 😄CRISTAL CLEAR explanation.
Like Bob, you have a rare gift to explain complicated things very well.
You don't happen to be a teacher?
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That's a great comparison, Scott.... Would I be correct in saying that the SD is always lower than the ES, providing you are looking at a reasonable number of shots.... For example, if you are looking at 10 shots, if the ES is 10 fps, then the SD would be less than 10 fps.... If you looked at 100 shots with a typical bell-curve distribution of velocities with an ES of 10 fps, wouldn't the SD likely be about 3 fps?.... since 3 x an SD of 3 = 99.7%....
Bob
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That's a great comparison, Scott.... Would I be correct in saying that the SD is always lower than the ES, providing you are looking at a reasonable number of shots.... For example, if you are looking at 10 shots, if the ES is 10 fps, then the SD would be less than 10 fps.... If you looked at 100 shots with a typical bell-curve distribution of velocities with an ES of 10 fps, wouldn't the SD likely be about 3 fps?.... since 3 x an SD of 3 = 99.7%....
Bob
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In a perfect distribution, and lots of shots, you should be able to work backwards and predict SD from ES.
SD will usually be less than ES, unless the sample is small. ES can only increase with more samples (more shots). SD stays about the same but gets more precise with greater number of samples.
The ES tells you the extremes of something you already did. The SD tells you what you are likely to do next.
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LOL! (chuckle)
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I get that.... So if we apply the idea of SD to estimating the range, or the windspeed, we would get the same thing.... We would have a prediction of how likely your next "guesstimate" is to the actual distance to the target, or how far the pellet will drift downrange, compared to the actual result.... These will typically be a bell-curve, so if over 100 range estimates you had an SD of 2%, then 99.7% of the time you should be able to estimate the range within 6%, correct?.... If over 100 estimates of the windspeed your SD was 10%, then 99.7% of the time you should be able to estimate the correct holdoff within 30%.... However, only 68.3% of the time would you get the range correct within 2%, or the drift correct within 10% (numbers for comparison only)….
The point of my article was to give a feel for how important velocity variation is to the vertical stringing at the target.... and how that compares to the human error involved in estimating range and windage.... I hope I accomplished that?....
Bob
PS, incidently, I used your calculator with a sample size of 2 shots, of 100 and 110 fps, and the SD was 7.07, while the ES was 10.... Increasing the number of shots to 20, with velocities all of 100 and 110, shrank the SD to just under 5.2 while the ES remained at 10.... I'm pretty sure the SD is always smaller than the ES.... It would appear, however, that an SD of 7 means that the velocity should be within plus or minus 7 fps, ie a total range of 14 fps, correct?.... In other words, an SD of 5 means that the ES would be 30, 99.7% of the time....
RBS
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The standard deviation calculation just provides you with information on how your data is distributed, which you don't get with the ES values. For a bell shaped distribution of data the ES values are by definition wider than the standard deviation. Bob, if you want to apply it to some of your historical data, Excel has the SD calculation as a built in function.
One of the interesting uses is evaluating errors at a common uncertainty level. For example if you have the standard deviation of the muzzle velocity and through your calculation it gives you a vertical error at 50 yds. If you have your range estimate standard deviation and calculated the corresponding vertical error at 50 yards, you can compare these at whatever confidence level you choose. Since these errors are independent of each other you can also start combining them using the root-sum-squared approach to get an estimate for the combined effect at that level of uncertainty (as opposed to just adding them). You can also start looking at separating errors. For example, lets say you shoot bench rest through a chrony, you may be able to separate out the velocity errors on target from the rest of the shot cycle errors..... Of course it is generally true that you can prove anything with statistics ;)
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It is also true that Statistics are like a Bikini.... What they reveal is enticing, but what they conceal is vital.... ;)
Bob
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I get that.... So if we apply the idea of SD to estimating the range, or the windspeed, we would get the same thing.... We would have a prediction of how likely your next "guesstimate" is to the actual distance to the target, or how far the pellet will drift downrange, compared to the actual result.... These will typically be a bell-curve, so if over 100 range estimates you had an SD of 2%, then 99.7% of the time you should be able to estimate the range within 6%, correct?.... If over 100 estimates of the windspeed your SD was 10%, then 99.7% of the time you should be able to estimate the correct holdoff within 30%.... However, only 68.3% of the time would you get the range correct within 2%, or the drift correct within 10% (numbers for comparison only)….
The point of my article was to give a feel for how important velocity variation is to the vertical stringing at the target.... and how that compares to the human error involved in estimating range and windage.... I hope I accomplished that?....
Bob
PS, incidently, I used your calculator with a sample size of 2 shots, of 100 and 110 fps, and the SD was 7.07, while the ES was 10.... Increasing the number of shots to 20, with velocities all of 100 and 110, shrank the SD to just under 5.2 while the ES remained at 10.... I'm pretty sure the SD is always smaller than the ES.... It would appear, however, that an SD of 7 means that the velocity should be within plus or minus 7 fps, ie a total range of 14 fps, correct?.... In other words, an SD of 5 means that the ES would be 30, 99.7% of the time....
RBS
"...These will typically be a bell-curve, so if over 100 range estimates you had an SD of 2%, then 99.7% of the time you should be able to estimate the range within 6%, correct?..."
Yes
"...The point of my article was to give a feel for how important velocity variation is to the vertical stringing at the target.... and how that compares to the human error involved in estimating range and windage.... I hope I accomplished that?...."
Yes you did.
"...It would appear, however, that an SD of 7 means that the velocity should be within plus or minus 7 fps, ie a total range of 14 fps, correct?..."
SD indicates a probability, not a certainty. An SD of 7 means that there is a 68.3% chance that the next shot will be within a range of +/- 7fps (or 14fps total spread).
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It is also true that Statistics are like a Bikini.... What they reveal is enticing, but what they conceal is vital.... ;)
Bob
+100
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Article #22 is online at H.A.M.... the first of 2 parts on pellet penetration....
https://hardairmagazine.com/ham-columns/airgun-pellet-penetration-the-real-story/
Enjoy!....
Bob
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The next article in my series is now online at H.A.M.....
https://hardairmagazine.com/ham-columns/the-effect-of-caliber-on-airgun-pellet-performance/
Bob
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Another great write up there Bob !!!
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Good stuff Bob.
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Congratulations and thank you!
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Article #24 is now online at Hard Air Magazine....
https://hardairmagazine.com/ham-columns/airgun-slug-penetration-compared-to-pellets/
It's hard to believe this marks 2 years as Technical Editor.... but I have to admit I am running out of topics!!!!
Bob
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Bob, 😊
another great article! THANKS!! 👍🏼
You give so much to our sport!
I truly hope that you'll eventually put all those articles into a book and sell it!
I'll buy 3, and would pay $20 each.
Matthias
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Stephen is considering that, I'll keep you all advised should it happen.... but I doubt it would be $20....
Bob
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The last article in my series on Ballistics is now online....
https://hardairmagazine.com/ham-columns/bob-sterne-discusses-hollowpoint-slug-design/
This is the 25th article I have written for H.A.M. and I am going to take a break from having to meet a deadline every month for a while.... When I have an idea for a stand-alone topic, or a short series, I plan to send them to Stephen, it just won't be monthly any more....
Bob
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The last article in my series on Ballistics is now online....
https://hardairmagazine.com/ham-columns/bob-sterne-discusses-hollowpoint-slug-design/
This is the 25th article I have written for H.A.M. and I am going to take a break from having to meet a deadline every month for a while.... When I have an idea for a stand-alone topic, or a short series, I plan to send them to Stephen, it just won't be monthly any more....
Bob
Another good read
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Here is an Index on Hard Air Magazine to all my articles:
https://hardairmagazine.com/ham-columns/the-definitive-index-to-bob-sternes-ham-technical-articles/
Bob
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Very convenient. Thanks.
The next index will be the index to your book, right?! 😄
Matthias
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That index is great. There's a lot of knowledge packed in there.
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There is a new article on H.A.M.... It deals with work by Miles Morris on possible drag models for typical airgun slugs....
https://hardairmagazine.com/ham-columns/some-new-airgun-slug-drag-models-by-miles-morris/
It is theoretical in nature, but provides some insight into the anomalous results we are seeing compared to the commonly used G1 drag model....
Bob
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I have just published a new article in H.A.M.... I discusses the difference in some of the Drag Models used in airguns, and why we need a new one!....
https://hardairmagazine.com/ham-columns/wind-drift-for-slugs-we-need-to-replace-the-g1-drag-model/
Using the G1 model will lead to incorrect trajectory and wind drift predictions for our slugs, which are capable of being used at higher velocities than is optimum for pellets....
Bob
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Thank you, Bob!
🔆 It's a joy to read such helpful articles as yours — you enrich our sport and increase the fun we get to have with our hobby!!
Matthias