POI shift (down) due higher muzzle speed

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explorer

explorer

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Jan 19, 2023
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Slovakia
Hey all,
I have a interesting topic here with ballistics speeds etc.
So my teory is:
Physically a faster shot with same projectile can not go lower (experience) POI shift down in comparsion to a slower one, even if its BC at higher speed is getting worse. (now excluding the barrel himp etc.)
Lets take an example:
We take two shots with 270m/s and 280m/s with same projectile. The projectile is exactly the same.
The faster projectile will experience after leaving the barrel worse BC due higher speed (higher drag) and its gonna loose the speed quicker than the slower one on the range but only till the moment when its getting slowed down to the speed of slower one 270 m/s. When its reaching the 270m/s the two projectiles are flying with same speed BC etc. But as long as the faster one was faster on the first few meters till it didnt slowed down to 270 m/s it was flying less time and experiencing less drop.

Im I right or the 280 m/s shot really can experience more drop on 50m for example than the 270 m/ one?
An important fact: We are talking about drop against the barrel line and not doing re-zero when switching to a slower speed. All environmental factors are the same (wind, humidity, temperature,etc.)
 
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explorer said:
The faster projectile will experience after leaving the barrel worse BC due higher speed (higher drag) and its gonna loose the speed quicker than the slower one on the range but only till the moment when its getting slowed down to the speed of slower one 270 m/s.
Click to expand...
The BC may start out lower but it will go up the arc and the BC will climb as it slows down. The faster shot will always be flatter. Wind drift on the other hand is a different story.

I'm sure there's a better way to word that but that's how I understand it.
 
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It's important to understand that POI (Point of Impact) is not the same as projectile drop. Vibration of the barrel and the rest of the gun control the POI, not the bc of the projectile. But the bc controls the drop.

I recently retuned my P35-25 for heavier projectiles. So I was testing 31 grain Baracudas, both 34.95 grain JSBs and some 26.8 grain Nielsen slugs I happened to have from testing other guns. The velocity was highest on the lightest projectile and followed the projectile weight. But the POI did not follow the same trend. The slug happened to be highest but Mark 1 JSBs impacted significantly higher than Mark 2 and Barracudas. That was not due to velocity or BC, it was due to vibration. I ran short of pellets but it appears Mark 1s are the most accurate. But I don't think that has anything to do with POI either.

But drop is pretty much bc. I can rezero for any of the projectiles and the drop will follow the bc of that projectile in my gun. That may or may not be the same as the published bc. Different rifling and probably other factors can easily cause a bc difference. But the bc is basically defined as how fast the projectile slows. Traveling slower means more drop. BC is calculated based upon the velocity drop over a measured distance.

At short range a gun not re-sighted between projectiles could easily have a faster projectile land above a slower one. Like Mark 1 JSBs did for me versus Baracudas. But that is just a zero issue, not an indication of a bc change. I usually sight in a 30 yards and was testing projectiles at that distance. BC doesn't have much of an effect at 30 yards. But at 100 yards, the higher bc is going to have less drop although velocity also matters and could have a bigger effect.

I look at chairgun to get an idea what to expect in terms of drop.
 
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JimD said:
It's important to understand that POI (Point of Impact) is not the same as projectile drop. Vibration of the barrel and the rest of the gun control the POI, not the bc of the projectile. But the bc controls the drop.

I recently retuned my P35-25 for heavier projectiles. So I was testing 31 grain Baracudas, both 34.95 grain JSBs and some 26.8 grain Nielsen slugs I happened to have from testing other guns. The velocity was highest on the lightest projectile and followed the projectile weight. But the POI did not follow the same trend. The slug happened to be highest but Mark 1 JSBs impacted significantly higher than Mark 2 and Barracudas. That was not due to velocity or BC, it was due to vibration. I ran short of pellets but it appears Mark 1s are the most accurate. But I don't think that has anything to do with POI either.

But drop is pretty much bc. I can rezero for any of the projectiles and the drop will follow the bc of that projectile in my gun. That may or may not be the same as the published bc. Different rifling and probably other factors can easily cause a bc difference. But the bc is basically defined as how fast the projectile slows. Traveling slower means more drop. BC is calculated based upon the velocity drop over a measured distance.

At short range a gun not re-sighted between projectiles could easily have a faster projectile land above a slower one. Like Mark 1 JSBs did for me versus Baracudas. But that is just a zero issue, not an indication of a bc change. I usually sight in a 30 yards and was testing projectiles at that distance. BC doesn't have much of an effect at 30 yards. But at 100 yards, the higher bc is going to have less drop although velocity also matters and could have a bigger effect.
Click to expand...
Sorry but its important to read the whole article also.
It's important to understand that POI (Point of Impact) is not the same as projectile drop.
Click to expand...
(now excluding the barrel himp etc.)

"I look at chairgun to get an idea what to expect in terms of drop."
-thats the case that chairgun not gonna tell you about BC change nothing as it has no idea about your projectile shape etc.
Sorry but you didnt understood the topic correctly.
Anyways, appreciate your willing to joing.
We are not comparing different projectiles in different environment tune etc. But two speed in same conditions. Without takind into account the barrel vibrations and other factors.
 
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explorer said:
Sorry but its important to read the whole article also.

(now excluding the barrel himp etc.)

"I look at chairgun to get an idea what to expect in terms of drop."
-thats the case that chairgun not gonna tell you about BC change nothing as it has no idea about your projectile shape etc.
Sorry but you didnt understood the topic correctly.
Anyways, appreciate your willing to joing.
We are not comparing different projectiles in different environment tune etc. But two speed in same conditions. Without takind into account the barrel vibrations and other factors.
Click to expand...
It appears there is a bit of mis-communication. I too did not understand the topic correctly, even though I attempted to read and understand the whole "article", your post. So thank you for the clarification.
If everything else is the same, the 280m/s projectile will have less drop at every given distance than the 270m/s projectile. That is the physics, as demonstrated for at least 300 years.
If you see more drop for the 280m/s projectile, please re-read JimD's post for explanations why.
 
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Another faulty inclusion in the original post is that the 280 m/sec projectile will ever be traveling slower than the 270 m/sec projectile. Even if it looses speed quicker it still will always be going faster than the initially slower projectile. If it impacts lower, it will be at close range and due to barrel harmonics not an assumed downward shift of bc.

While air resistance is increased by higher speed it is only one factor in determining bc. I don't think it is safe to assume it will always be lower due to a 10 m/sec increase in velocity. If the bullet tips a little that would be a more important factor. If the rifle "likes" the higher velocity better and launches the projectile straighter the bc might actually be higher at the higher speed.
 
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When i chase POI around with my Maverick, things generally tend to move in all 4 directions.

So i might end up clicking 2-3-4 times to the left, and catch up,only to have it jump back ( maybe not all the way in one huge jump ) a few shots later, and at the same time things might also move up and down a little, though this i feel are to a lesser degree.
But then some times i can get POI to not move, well at least enough to shoot a good 5 shot group,, maybe 2 in a row if i am really lucky, and i would like to say by lowering the speed, but its not really true CUZ a setting that was once good, will start to shift POI again, i have NEVER been able to set a tune for the Maverick that last several outings, not even in summer with fairly stable weather for the sessions.
It seem like i always have to turn some knob on that GD rifle.

I have even tried to always start with a cleaned barrel, and so having to lead in a little, but even starting from 0 on this parameter too dont seem to make any sense.
So ! i am very eager to try something else, CUZ my Maverick while i shoot it the most, and its not like in the start, then it is still nagging me all the time.

I am also amazed i do not hear this from other FX shooters, which just get me thinking that i must be stupid. ( CUZ from my childhood traumas i am endowed with a huge sense of self criticism )

I so wish i had a rock solid bench, CUZ then i would clamp / nail / boldt / weld that damn Maverick down, and then shoot it knowing i have 100 % eliminated any scope / cant / shooter / whatever error.
 
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