Pellet and Slugs BC's and the Aerodynamic Point Of Inflection explained

This is the same shooter from Chile as above shooting the same .22 slugs at 200 Meters....



https://www.youtube.com/watch?v=YNI4xprBXzQ





At 100 meters he shot a slightly larger group than 2-2.5 Inches and at 200 it doubled+ that group to around 5-6 inches...

Not bad at all but not nearly the precision of a rimfire at 100 M....I've never tested a .22 RF for groups at 200 Meters and I probably never will, I am just not really interested in precision shooting at 200 M with a .22 RF or an air gun.

Regards,

AZ

AZ, when you were referring to mold release agents if you watch AEAC JSB factor tour you will see the the die/mold release application before swaging, then after the sorters are actually toweling off some of the access! “ that seemed to surprise Steve” I don’t even weigh them any more, just inspect for badly damaged heads & skirts! About the only thing that seems to make a big difference in accuracy in my BM-500 is the depth of the skirt pockets? I think you know what I’m referring to... ( I used to believe it was head Dia. But not not anymore)

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nomojo65:

Overtime we have heard so many things and we have been indoctrinated into many myths (many of them plain marketing) that if you bring all that crap to present time, many people have a hard time believing or listening otherwise...When we discuss things some people convey good info, but not everyone out there is willing to listen.

If you think about the pellet lubricants supposedly increasing accuracy (among other "magic" properties), why would it improve accuracy?...If you put lube on your pellets it will eventually lube the entire bore, when you lube your bore velocities DROP most of the times, the only instances when velocity increases is when the pellets have a tight fit to the bore...Lube does nothing for the pellet engaging the rifling and has absolutely no aerodynamic effects (I read somebody saying that lube on the surface would alleviate much of the turbulence on the pellet's surface)....

So if a drop in velocity or a slight increase is what improved your accuracy, you might as well increase/decrease the velocity of your gun and shoot non-lubed pellets, save yourself messy bores to clean, spend the magic potion's money in pellets, and spend that magic pellet "Preparation time" shooting, don't you think?...But then there is a pellet lube industry that will fiercely attack you if you say so because they have the "Magic Potion" that will give you the edge and they want your money...

The same happens with pellet re-zing dies...If you resize the head, KAPUT!, don't expect most precision....Then, why would you resize a skirt when your barrel will do it automatically and for free?...If you load a larger skirt, upon you loading it into the breach the barrel will re-size it to the exact dimensions needed!!!...And then if the pellet is undersized, with the initial blast of air coming out of the port the skirt will expand to the exact dimensions you need at the exact time it starts moving, it is less effort for the blast to expand the skirt to fit the bore than it is for pushing it forward!!

Lots of myths preached as facts, conceptual errors & misunderstandings of scientific facts (reason for this thread) and stuff like abound in these gun forums, and if you pay attention, people seem to ask the same things time and again...I wonder if they don't read or if their RAM memory is not functioning...But I guess that sometimes is better to keep our mouths shut, neither of us needs more free enemies...When I was a teenager and got my first job, I learned from a very smart peer: "Let the world turn around and don't interfere or try to spin it from "East to West"...He would never ever contradict anyone, "So be it" was his favorite slogan no matter what he heard or what he was told...He was the most popular guy in town with lots of friends!  

I weigh when shooting 50 or more with low 12 ft./lb. or even 20 ft./lb because a minute 1/2 grain difference means a flier and the same when shooting 100 EBR style paper targets, I weigh and size when a serious competition, usually at 25 M and I don't weigh nor size for silhouettes at 40-50-60 & 70 Meter (too big of a kill zone in those targets) and neither for shooting informal BR matches or competitions...My guns don't differentiate in between normal and re-designed pellets nor head sizes within normal parameters (4.48 - 4.54), they shoot them all very precisely and this makes my life easier.

Regards and take care,

AZ

AZ, when you say "size" I'm assuming that is just the skirt of the pellet? What tool do you use? Isn't the skirt always larger than the head?

My next question is if the skirt will form to the bore anyway then why size the skirt? 

I think I'm missing something somewhere here but don't know what.

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Steve:

I get "Mental lapsus" once in a while!  ...Too many things going on and I am using an iPad because I didn't bring my Laptop...

When I sometimes say SIZE I mean head gauging or head sizing, I don't measure skirts as mentioned in this thread, skirts are sized to the bore whether they are larger or smaller: When loading an over sized skirt into the breech it re-sizes it to the bore dimensions, and if the skirt is under-sized the HP air will take care of that at the same time the pellet is pushed forward into the barrel...

For practical issues I use a PELLET GAUGE for the heads at home...But then if I need to do several thousand I take them to the lab and one of the tech assistants will use optical comparators, or laser mics, or air gauging (whatever is not being used)...All provide the same results. At home a Pellet Gauge will allow me to measure a 500 pellet tin in about 1 hour (not too bad), at the lab they will do 3000 - 4000 in one hour per station (operator/machine). 

Regards,

AZ

Welcome back...In my original post in this thread, I said: 

Note: I am looking forward to seeing the posts and videos of the so called "Forum Experts" explaining this fight and taking the credit for it. 



Well, it didn't take long for that to happen ...Today Matt Dubber uploaded a video explaining this thread (link provided at the bottom of this post)...There are some points in his hyphotesis that are a little confusing in the sense that goes back and forth even with hyphotess that are at error, but each and everyone of us has a different way to communicate what we are trying to say and some people might not understand the way I express myself either.

In my original post I believe that I explained more clearly and straight to the facts the issues with Nutation and Precession and why it happens...For anyone who still doesn't understand the first post in this thread, let me summarize it kind of like kitchen receipees: Note: I recommend to read the first post in this thread so you understand the terminology and concepts.

Note: I don't work for anybody in the industry so you will not hear me enforcing brands and products, that is a consumer's choice preferably based on testing experience more than MARKETING..

1. Pellets are stabilized by drag or by drag and rotation and slugs by rotation...Velocity is DEFINITELY (Science fact) a factor in stabilization, the point of inflection explained in the first post of this thread is the consequence of spiraling (I will use the term "spiraling" for both: Nutation and Precession). 
2. Higher velocities (pellets) can and will in most instances have a lower BC as distances increase (medium range), but then then BC's can go up again depending on the initial muzzle velocity...The higher the muzzle velocity the higher the initial BC. The reason for this is that the BC is high at the muzzle because velocity is exagerating the aerodynamic design of the pellet, so then this BC is basically ARTIFICIAL and not high becasue the design of the pellet. When the pellet reaches the PELLET DESIGN VELOCITY, the BC drops to the nominal BC.
3. Twist ratios DEFINITELY have an effect in spiraling (Science Fact)...By design a pellet will very seldom get into spiraling when shot from a SMOOTH barrel, the reason for this is that there is no "Shock" (point of inflection as explained in the first post) where rotation is overtaken by drag...A pellet shot from a smooth bore can spiral, but this may happen when the pellet loses its DRAG stabilization (it never had rotation), and for a pellet to loose drag stabilization a VERY LOW velocity is required. Most pellet designs don't loose DRAG stabilization before reaching 180-200 fps. if wind is present, and sometimes they don't destabilize at even velocities close to zero; here is where WIND has more impact in the equation: A low velocity pellet stabilized by drag will normally (depending on the design of the pellet) NOT spiral unless wind velocity overcomes the remaining drag stabilization at that very low pellet velocity, meaning that at this point the BC is close to zero. 
4. The slower the barrel the more velocity is required for precision at farther distances
5. A faster barrel can shoot at lower velocities better than a slow or a smooth barrel at farther distances (As distance increases)
6. A slow barrel is better that a faster barrel at medium distances given the same parameters of velocity and projectile design up to the point where the point of inflection is not present. After encountering the POI, the faster barrel will outperform it.
7. A slower barrel at longer distances needs more velocity than a faster barrel at the same distance to attain the same BC and precision.
8. There is a point where the BC's of a faster barrel at low velocity, and a slower barrel at high velocity are equal...At this point both barrels will shoot the same
9. Spiraling is positively correlated to velocity, the higher the velocity the longer it will take for that pellet to spiral
10. Slower barrels are good up to a certain distance where drag takes over,at this point the pellet may still flight true, but DRAG stabilizatiion is less precise than rotation at comparable distances.
11. The trancistion TIME between drag and rotation stabilization is longer in a FASTER barrel. This means that the point of inflection coming from a faster barrel will be longer in time (unstabble for a longer time interval) and will have more impact in precision.
12. You want a barrel to have the POI (point of impact) at a farther distance than the distance that you are shooting
13. The point of inflection has more effect in a faster barrel, but a faster barrel can shoot at much farther distances than a slower barrel (both shooting at the same velocities) before the pellet reaches the point of inflection. In other words: A faster barrel will shoot more precise than a slower barrel after the distance where the point of inflection was present in the slower barrel
14. For farther distances VELOCITY is the key factor, the higher the muzzle velocity the higher the muzzle BC...This is why many times we see a pellet with a high BC at the muzzle that drops at intermediate distances and then increases at farther distances...
15. Guns shooting at very low velocities at short distances from about 10 M to 20-25 M shoot better with a faster barrel vs. a slow barrel or a full smooth bore. 10M top guns (Feinwerkbau 700-800, Anschutz 9015, Walther, etc) all use 1:12 to 1:14 TR's which are considered FAST barrels in the airgun industry.
16. There is NO SECRET for shooting slugs: Let's not listen to the "Mumbo Jumbo" secrets out there...It is as simple as this: A barrel with no choke will shoot solid base slugs better than a choked barrel, a choked barrel will shoot hybrids (slugs with cup dish or holow base) better than a barrel with no choke...A very minimum choke might help certain solid base slugs...AS SIMPLE AS THAT! and I really don't care who says what.
17. Twist ratios for slugs follow the same principles and routes that rimfire and centerfire barrels follow...You are simply shooting a bullet with a different propellant, so whatever works for powder burners will work for airguns shooting SOLID BASE slugs.
18. If you want to know the best TR in a barrel for a certain slug, get into any of the software programs that barrel/bullet manufacturers post on their web sites for estimating the twist ratio required for their bullets...You don't need airgun GURUS to tell you whatever is convenient for their marketing efforts.
19. There is much hype regarding sub sonic, transonic and supersonic speeds.. No such thing, ALL projectiles, airplanes, rockets, missiles, bullets and pellets to name a few, have a VELOCITY design...If supersonic velocities were a problem, ALL Centerfire and many Rimfire bullets would have a problem at the crown of the barrel (where the bullet breaks the sound barrier)...THEY DON'T because those projectiles are designed for stability at breaking in and supersonic velocities. True is that when a projectile breaks the sound barrier it generates a shock wave that "mounts" over the surface of the projectile and stays there while at supersonic speed, but then when speed drops to near transonic speeds (sound speed), the shock wave over the projectile starts to "strip off" the projectile and this is where unstability happens.
20. Transonic speeds affect more coming from supersonic to subsonic than going from subsonic to supersonic (Scientific fact). In other words, the acceleration has more impact than the deceleration, but it wouldn't make sense to design gun projectiles to perform at the deceleration stage (it is possible but not done)
21. The points above (19 and 20 ) affect powder burners more than the airgun industry because pellets are very seldom shot at supersonic velocities.
22. The BEST ballisticians in the world are at NASA and NOT around the airgun shooting industry...Watch out for "hype" with marketing agendas
23. The list goes on and on but I believe that after post number 1 in this thread added to this post, the shooter will NOT need advice from anyone to determine what works best for Him-Her.
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    You all stay safe...
    
    Regards,
    
    AZ
    
    This is the link I referred:
    
    https://www.youtube.com/watch?v=pR5j4aZwNH0&t=519s
    
    

Outstanding thread. Many of your points I agree with, okay all but one.

The BEST ballisticians in the world are at NASA and NOT around the airgun shooting industry…Watch out for "hype" with marketing agendas

And I may be partial because I worked there. US Army Research Laboratory. The ENIAC was used in the building I worked. My range time is limited to ten years and no airgun projectiles. The guy that mentioned the army manuals, I’m betting he misremembered some of those terms and definitions you mentioned are in there.

I worked in the experimental design and conduct branch in survivability lethality and analysis, at Air base experimental facilities (test ranges) we’d do full dynamic test on rotary wing aircraft. (I’m not taking anything away from buddies at Embry Riddle and NASA, but Army has been doing it a lot longer and talking about rifles we stomp them, sure they win on rockets and aircraft) 



But the joy and satisfaction of seeing a post from a non biased engineer is appreciated. I think we need to make a sticky here. Just from the posts I think it would of been great to have you at our facilities and to see yours. Different goals, similar principals, same rigor for truth. 



I hope hope you have a great weekend, I’d love to hear more, this gets me more excited then shooting.

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