The Mysterious BC compliments of Ted
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Wingnut...
But thank you for your work! Makes it a little bit less expensive for the rest of us.
You rock!
Allen
But thank you for your work! Makes it a little bit less expensive for the rest of us.
You rock!
Allen
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Deriving the BC from a POI change is valid only from the same state of tune. Changing the state of tune influences the recoil characteristics of the gun in unpredictable ways (e.g. barrel harmonics, muzzle flip, etc.) and therefore has the potential to produce very misleading differences in POI.
In Ted's example, he moves it from 1000fps to 1100fps which amounts to a significant increase of muzzle energy of 20%. Much more air delivered during the shot cycle...much different movement from the gun and the barrel.
In Ted's example, he moves it from 1000fps to 1100fps which amounts to a significant increase of muzzle energy of 20%. Much more air delivered during the shot cycle...much different movement from the gun and the barrel.
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So , one would have to use something like a Labradar or chronograph at the target to confirm whether indeed there is a change?
Allen
Allen
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Yes the delta V method is a good way of doing it. Two chronographs (calibrated against each other), one near the muzzle and another far downrange. Or as you said, a chronograph like Labradar that can take two readings.
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I calculate BC using just one chronograph. Shoot at least ten shots at the muzzle and then get an average velocity. Then do it again at two known distances down range. With three readings down range you will have some very valuable info to feed into your ballistic program. You will also find that the BC derived from the muzzle to point A and then from point A to point B will have changed.
Kenny
Kenny
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KG and if correct thats where it gets fun and there are those that geek out and those who just say whatever! This is where a Labradar is handy. At what speeds two points is the bc the highest ( well of course probably at the beginning) and at what speed does the bc begin to make major changes? How far does it travel before doing so? Does it remain stable? At what speed is it when it is not stable. How far does it travel before this happens? Is it because it lost its spin? Is it because of the current spin rate is what it is that it works so well? 
I'm sure there are those that are totally more geeky than me. And with my ADD I can only go so far before "Look a squirrel!"
Allen
I'm sure there are those that are totally more geeky than me. And with my ADD I can only go so far before "Look a squirrel!"
Allen
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Allen-
I’m kind of like you. I find it all very interesting but at some point I just want to go shoot something. “Look… a squirrel!” I did indeed find that the closer higher velocity readings gave a higher BC which then dropped as velocity was reduced. That was shooting the NSA 24.8 grain slug at 7500 foot elevation.
Kenny
I’m kind of like you. I find it all very interesting but at some point I just want to go shoot something. “Look… a squirrel!” I did indeed find that the closer higher velocity readings gave a higher BC which then dropped as velocity was reduced. That was shooting the NSA 24.8 grain slug at 7500 foot elevation.
Kenny
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I understand how the velocity of the pellet/slug might have a effect on group size (e.g. barrel harmonics, muzzle flip, etc.) , but I don’t think that is what Ted is describing.
Sure, it could be that “barrel harmonics, muzzle flip, etc.” are the most likely reason(s) for the groups shrinking as the velocity is dialed up. Totally agree. But. After the projectile leaves the barrel, “barrel harmonics, muzzle flip, etc.” have zero effect on the trajectory.
You might be able to make the case for “barrel harmonics, muzzle flip, etc.” being the reason for the POI difference at 100 yards, except for the fact that Ted said he re-zeroed at 50 yards before shooting the 100 yard groups. With a 50 yard zero for both tunes, the slugs have to follow the trajectory path determined by the muzzle velocity and BC.
A POI change like Ted describes can only be explained by a change in BC..since the velocity change alone cannot explain it.
A doubling of the BC seems crazy, but there is probably something related to the slug drag envelope as is hits a certain velocity..unless of course, Ted just made a mistake in his testing results.
It would be great if someone else could duplicate similar results.
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So I went ahead and typed up the data with StrelokPro
I didn’t change the bc from the data in StrelokPro simply because I don’t believe it changes.
I believe this is simply a factor of a very high scope “3.75”
And messing with the near and far zero changing with fps changes
Here are the screenshots showing the near and far zero.
3.75” scope height
50y zero
14 twist
1000fps
10y and 170y
And at 1100fps
10y and 190y
What do u think?
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I think you're on to something. If at 1100 FPS the slug is still RISING from a 50 yard zero, then of course the 100Y will be higher than 1000 FPS where the slug is at its zenith with a 50Y zero... Makes sense to me, but that's only IMO...
I'll bet if he set a 75 yard zero for both speeds he'd see a similar BC. Or, like I said, just use Lab Radar to save on brain cells...
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Only thing no one said is form factor ? Normally BC can change a small percentage with variables but I never saw double , one question was this checked on G1 or G7 cause can be huge difference in the BC \ DID you use G7 ?
I do not own same set up to test what is said .
LOU
I do not own same set up to test what is said .
LOU
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To take it a step farther
Here’s the same data with 1100 fps and .18 bc
I think he just increased the bc till it matched what he saw on target.
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You’re right. I misunderstood when I watched it the first time. I thought he was extrapolating between two different states of tune. My apologies for adding to the confusion already swirling, and thank you for the polite correction.
Looking back at Ted's video again just now, I notice in his Chairgun screenshots that he is using a custom drag profile...which means there is a very simple but not so satisfying answer: the drag profile is wrong. If it were correct, the BC would not vary with velocity. That's the whole point of a drag profile.
Elsewhere Bob Sterne pointed out that ballistician Miles Morris found the commonly used G1 profile is wildly off in the transonic region for typical slugs, so if Ted used it as the starting point for his custom profile, that would represent a significant source of the discrepancy.
The good news here is that drag doesn't mount up nearly as quickly as we approach the speed of sound as we might have expected based on the "best we got right now" G1 profile.
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No worries. Definitely no apology required.
I missed the "custom drag profile"..good catch. Yet another reason I'm getting an eye exam in a few weeks.
Thx for the mention of ballistician Miles Morris..I was able to search and find some links to what I assume will be "light reading"..lol
@Centercut
Also think you my have something on the 50yd zero.
I think I'm moving to the other thread so we don't continue to play thread pong.
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Ted, just get a Labradar on the job and retest. Let's see it on video as well. Easy for me to say 
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OK, so I don't know much about physics or how liquids like air perform. However, I am fascinated by this stuff.
Youtube channel Smarter Every Day did some work on subsonic vs supersonic shooting a while back here:
At 1100 fps, and 900 feet altitude, the slug may have gone supersonic for a bit, changing everything. In the video above, when approaching the speed of sound, some of the air flow did achieve supersonic speeds. according to the bit at approximately 5:14 into the video. The photography shows shock waves that look like supersonic though the bullet is subsonic. So even if the whole slug didn't go supersonic, perhaps some airflow did.
So, if that's happening, and you are achieving supersonic on some airflow, that does change everything.
Youtube channel Smarter Every Day did some work on subsonic vs supersonic shooting a while back here:
At 1100 fps, and 900 feet altitude, the slug may have gone supersonic for a bit, changing everything. In the video above, when approaching the speed of sound, some of the air flow did achieve supersonic speeds. according to the bit at approximately 5:14 into the video. The photography shows shock waves that look like supersonic though the bullet is subsonic. So even if the whole slug didn't go supersonic, perhaps some airflow did.
So, if that's happening, and you are achieving supersonic on some airflow, that does change everything.
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Ok, now i m hesitating again. When seeing this subsonic-supersonic differences in air movement, subsequently those explanations on the white board with subsonic for a brief ‘transsonic' moment becoming supersonic in its waves-movements.
‘Transsonic”? Wth ?
Got to say i never knew this.
So just to make sure i understood this right, please correct me if i m interpreting wrongly :
A subsonic – but very close to supersonic – traveling bullet creates supersonic shockwaves for a very-very brief moment pulling/jerking the subsonic bullet into supersonic flight, immediately after that going subsonic again.
Or did i miss something?
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