gcamp54
Well-Known Member
I do my load development at close to sea level. When I go up in altitude my velocity increases. Does this increase my chamber pressure?
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Chamber pressure changes with altitude
- Thread starter gcamp54
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No. The increase in velocity is due to the thinner atmosphere. Less resistance for the bullet to cut through.
gcamp54
Well-Known Member
I assumed that was the case. Wanted to confirm it though. You know what they say about assuming. Thanks.
BallisticsGuy
Well-Known Member
A point of clarification: Chamber pressure won't increase but the pressure differential between inside the bore and outside it will be higher. That's mostly immaterial but an interesting point as it means the pressure vessel will undergo increased stress in containing the high pressure. In the parts of the troposphere that humans inhabit the difference is so small as to be negligible for everyday purposes but it's an interesting point nonetheless.
Michael Eichele
Well-Known Member
There is more to the answer than just yes or no.
Having a lot of air space in the case can affect your velocity as you go up in elevation or down in elevation (temperatures being the same).
This is one of the reasons I try to develop hunting loads with as full a case as possible. I live, develop loads and shoot near sea level most of the time whereas most of my hunting is at 5,500-8,500' and on occasions as high as 11,000'. I travel with a chronograph when I travel for hunting and always hit a rifle range to check zero and velocity. In every instance, having loads with poor load densities have always yielded higher velocities at higher elevations. Talking to the Huskemaw guys in Cody, they indicated they have experienced the same effect in the opposite direction in some loads since they develop at 5000+ feet and then travel to lower elevations near sea level, they're loosing velocity in some loads. I don't experience this with loads that have a high load density. Everybody is always worried about temperature sensitivity but often overlook elevation changes.
Something to think about.
Scientific proof? No. Pattern? He!! yes.
M
Having a lot of air space in the case can affect your velocity as you go up in elevation or down in elevation (temperatures being the same).
This is one of the reasons I try to develop hunting loads with as full a case as possible. I live, develop loads and shoot near sea level most of the time whereas most of my hunting is at 5,500-8,500' and on occasions as high as 11,000'. I travel with a chronograph when I travel for hunting and always hit a rifle range to check zero and velocity. In every instance, having loads with poor load densities have always yielded higher velocities at higher elevations. Talking to the Huskemaw guys in Cody, they indicated they have experienced the same effect in the opposite direction in some loads since they develop at 5000+ feet and then travel to lower elevations near sea level, they're loosing velocity in some loads. I don't experience this with loads that have a high load density. Everybody is always worried about temperature sensitivity but often overlook elevation changes.
Something to think about.
Scientific proof? No. Pattern? He!! yes.
M
I can't think of any altitude factor related to different atmospheric pressure and air density that would account for higher or lower chamber pressures and MV. I've read posts from seasoned shooters that claim to have observed MV change with elevation. No poster has identified the cause, or if they know the cause, they've not communicated it.
Could MV change with changing altitude be air density related? No, air density won't cause a significant change in MV over the distance from the muzzle to the chronographs, and even if it did, correcting the chrono velocity back to the muzzle will factor in the actual air density if the correction if performed properly. If a MagnetoSpeed is hung off the muzzle, the only length of bullet travel in the differing air density is the barrel length. Not enough to register on a MagnetoSpeed.
Could MV change with changing altitude be oxygen availability related? No, gun powder and primers contain their own oxidants. Atmospheric oxygen isn't utilized.
Could MV change with changing altitude be temperature related? Possibly, if temperatures change substantially, power burn rates can change, bore diameter can change, and the bore to bullet friction can change. But any temperature affects should be the same regardless of the altitude. In other words, the causative effect on MV would be temperature related. Not altitude related.
None of the posts I've read claiming "altitude" affects MV were ever posted by a researcher, or anyone else that claimed to have set out to conclusively measure altitude caused changes in MV. Based on the content of the Posts, they were all based on anecdotal evidence.
From Wikipedia:
Anecdotal evidence is evidence from anecdotes. Where only one or a few anecdotes are presented, there is a larger chance that they may be unreliable due to cherry-picked or otherwise non-representative samples of typical cases.[1][2] Anecdotal evidence is considered dubious support of a generalized claim; it is, however, within the scope of scientific method for claims regarding particular instances, for example the use of case studies in medicine.
Introduction
In all forms of anecdotal evidence, its reliability by objective independent assessment may be in doubt. This is a consequence of the informal way the information is gathered, documented, presented, or any combination of the three. The term is often used to describe evidence for which there is an absence of documentation, leaving verification dependent on the credibility of the party presenting the evidence.
Scientific context
In science, definitions of anecdotal evidence include:
"casual observations or indications rather than rigorous or scientific analysis"[6]
"information passed along by word-of-mouth but not documented scientifically"[citation needed]
Anecdotal evidence can have varying degrees of formality. For instance, in medicine, published anecdotal evidence by a trained observer (a doctor) is called a case report, and is subjected to formal peer review.[7] Although such evidence is not seen as conclusive, it is sometimes regarded as an invitation to more rigorous scientific study of the phenomenon in question.[8] For instance, one study found that 35 of 47 anecdotal reports of drug side-effects were later sustained as "clearly correct."[9]
Anecdotal evidence is considered the least certain type of scientific information.[10] Researchers may use anecdotal evidence for suggesting new hypotheses, but never as validating evidence.
I view the claims that altitude changes rifle MV in the same category as the once long held belief among many experienced shooters and riflemen that some rifles, with some bullets, are capable of improving precision at longer ranges. Improving precision would mean either smaller measured group sizes farther from the muzzle, or lesser group sizes expressed in smaller units of angular measurement farther from the muzzle. Brian Litz effectively put this claim to rest when he devised a method to test these claims empirically, by measuring the same fired bullet groups at closer range, and then again at a farther range. He couldn't demonstrate this claim. He challenged anyone who believed they possessed a rifle / bullet / load combination that displayed improving precision at greater distances to travel to Michigan, where he would test the rifle on his shooting range. Brian would fund all associated expenses to anyone that produced such a rifle on his shooting range which demonstrated improving precision at increasing range. This was close to 2 years ago and the Thread went stale long ago with no one reported to have provided Brian with a rifle for testing. This long held belief was based exclusively on anecdotal evidence and word of mouth stories passed along over the years. It was repeated by knowledgeable shooters so often, for so long, that it was accepted as proven fact. As soon as Brian developed a scientific method to test this anecdotal evidence-based claim, the claim was damaged beyond salvaging.
Could MV change with changing altitude be air density related? No, air density won't cause a significant change in MV over the distance from the muzzle to the chronographs, and even if it did, correcting the chrono velocity back to the muzzle will factor in the actual air density if the correction if performed properly. If a MagnetoSpeed is hung off the muzzle, the only length of bullet travel in the differing air density is the barrel length. Not enough to register on a MagnetoSpeed.
Could MV change with changing altitude be oxygen availability related? No, gun powder and primers contain their own oxidants. Atmospheric oxygen isn't utilized.
Could MV change with changing altitude be temperature related? Possibly, if temperatures change substantially, power burn rates can change, bore diameter can change, and the bore to bullet friction can change. But any temperature affects should be the same regardless of the altitude. In other words, the causative effect on MV would be temperature related. Not altitude related.
None of the posts I've read claiming "altitude" affects MV were ever posted by a researcher, or anyone else that claimed to have set out to conclusively measure altitude caused changes in MV. Based on the content of the Posts, they were all based on anecdotal evidence.
From Wikipedia:
Anecdotal evidence is evidence from anecdotes. Where only one or a few anecdotes are presented, there is a larger chance that they may be unreliable due to cherry-picked or otherwise non-representative samples of typical cases.[1][2] Anecdotal evidence is considered dubious support of a generalized claim; it is, however, within the scope of scientific method for claims regarding particular instances, for example the use of case studies in medicine.
Introduction
In all forms of anecdotal evidence, its reliability by objective independent assessment may be in doubt. This is a consequence of the informal way the information is gathered, documented, presented, or any combination of the three. The term is often used to describe evidence for which there is an absence of documentation, leaving verification dependent on the credibility of the party presenting the evidence.
Scientific context
In science, definitions of anecdotal evidence include:
"casual observations or indications rather than rigorous or scientific analysis"[6]
"information passed along by word-of-mouth but not documented scientifically"[citation needed]
Anecdotal evidence can have varying degrees of formality. For instance, in medicine, published anecdotal evidence by a trained observer (a doctor) is called a case report, and is subjected to formal peer review.[7] Although such evidence is not seen as conclusive, it is sometimes regarded as an invitation to more rigorous scientific study of the phenomenon in question.[8] For instance, one study found that 35 of 47 anecdotal reports of drug side-effects were later sustained as "clearly correct."[9]
Anecdotal evidence is considered the least certain type of scientific information.[10] Researchers may use anecdotal evidence for suggesting new hypotheses, but never as validating evidence.
I view the claims that altitude changes rifle MV in the same category as the once long held belief among many experienced shooters and riflemen that some rifles, with some bullets, are capable of improving precision at longer ranges. Improving precision would mean either smaller measured group sizes farther from the muzzle, or lesser group sizes expressed in smaller units of angular measurement farther from the muzzle. Brian Litz effectively put this claim to rest when he devised a method to test these claims empirically, by measuring the same fired bullet groups at closer range, and then again at a farther range. He couldn't demonstrate this claim. He challenged anyone who believed they possessed a rifle / bullet / load combination that displayed improving precision at greater distances to travel to Michigan, where he would test the rifle on his shooting range. Brian would fund all associated expenses to anyone that produced such a rifle on his shooting range which demonstrated improving precision at increasing range. This was close to 2 years ago and the Thread went stale long ago with no one reported to have provided Brian with a rifle for testing. This long held belief was based exclusively on anecdotal evidence and word of mouth stories passed along over the years. It was repeated by knowledgeable shooters so often, for so long, that it was accepted as proven fact. As soon as Brian developed a scientific method to test this anecdotal evidence-based claim, the claim was damaged beyond salvaging.
Michael Eichele
Well-Known Member
Maybe you should be the first!
This could definately become a heated discussion. I really don't have the time, patience or energy to waste on who's right or who's wrong. At this point in my life I'm satisfied that I took the time, patience, energy and money to verify my loads at different altitudes as well as hot and cold temperatures which is what any responsible long range hunter should be doing anyway instead of arguing about it.
If one has questions about this topic, the best thing to to is get out there and test it for yourself. You don't need to publish a paper or have an engineering degree. If you can load ammo consistently and read a chronograph, you can find the results for your personal rifle ammo combo.
While it would be wonderful to know exactly why and the science behind it, the reality is, we just need to know what our ammo is doing where we are hunting. Nothing more. Nothing less.
Paul, have you tested your ammo at different altitudes? Just a question. Not an attack.
This could definately become a heated discussion. I really don't have the time, patience or energy to waste on who's right or who's wrong. At this point in my life I'm satisfied that I took the time, patience, energy and money to verify my loads at different altitudes as well as hot and cold temperatures which is what any responsible long range hunter should be doing anyway instead of arguing about it.
If one has questions about this topic, the best thing to to is get out there and test it for yourself. You don't need to publish a paper or have an engineering degree. If you can load ammo consistently and read a chronograph, you can find the results for your personal rifle ammo combo.
While it would be wonderful to know exactly why and the science behind it, the reality is, we just need to know what our ammo is doing where we are hunting. Nothing more. Nothing less.
Paul, have you tested your ammo at different altitudes? Just a question. Not an attack.
I don't dare... The result would lay another myth to waste, created and perpetuated based on anecdotal evidence.
And some prefer to believe and trust in myths. Why disappoint the believing?
Michael Eichele
Well-Known Member
That's a cop out. Or maybe you don't want to see a possibility that there's something real there? What's the harm? You could always keep the results to yourself so you don't disappoint anybody else.
I don't get heated. I get logical. And logic prevails - between the two - every single time.
You don't wanna hear the scientific explanation as to why I won't waste my time trying to disprove a clearly false myth. It would only cause more heat.
You're carrying on as if I'm obligated to meet a standard of performance set by you. That's what happens when people get heated. Unrealistic impositions and demands. Try logic.
You don't wanna hear the scientific explanation as to why I won't waste my time trying to disprove a clearly false myth. It would only cause more heat.
You're carrying on as if I'm obligated to meet a standard of performance set by you. That's what happens when people get heated. Unrealistic impositions and demands. Try logic.
Michael Eichele
Well-Known Member
When other members use logic you discredit their experiences and argue with them when their logic doesn't meet your logic. Who get to say who's logic is right and who's is wrong? You and I have differing opinions here. No big deal. In my mind, logic says it's possible. Testing showed me it can happen. It's logical to me. Just because it's not logical to you, doesn't mean it's right or wrong and the same applies to me. Who's logic is right?
The original poster can clearly see that some say no. Others say is can. Now it's up to him to decide to take it to the next level and check it for himself.
The original poster can clearly see that some say no. Others say is can. Now it's up to him to decide to take it to the next level and check it for himself.
Here's logic. Small arms fire has been studied to death for generations, not years. For national defense purposes. The armed forces want to know and pay good money to find out.
Ballisticians recognize the affects of temperature on powder burning rates, and provide compensation for MV in their programs based on differing station temperatures. If altitude, in and of itself, affected MV in a statistically meaningful, and therefore consistent, reliable, and repeatable fashion, wouldn't the armed forces researchers and someone like Bryan Litz who earns a portion of his living studying and educating shooters of all walks and trades have documented the altitude affect on muzzle velocity with scientifically defensible means and methods? And after having documented the relationship between altitude and MV, then include an algorithm into ballistics programs to model the affect of altitude on MV for the benefit of the troops, or customers?
Small arms ballistics programs include algorithms for temperature, angle of fire, coriolis drift, wind speed, wind direction, spin drift & rifling twist rate, rifle cant, station pressure, humidity, and on and on. Each of these factors are proven, not with anecdotal evidence and old wives tales passed along over years and generations, but based on defensible science that can be repeated by any other qualified person employing the same scientific methods.
Why is there no MV correction based strictly on station altitude??? Logic will lead one to the obvious conclusion. Altitude in and of itself has no affect on MV.
Ballisticians recognize the affects of temperature on powder burning rates, and provide compensation for MV in their programs based on differing station temperatures. If altitude, in and of itself, affected MV in a statistically meaningful, and therefore consistent, reliable, and repeatable fashion, wouldn't the armed forces researchers and someone like Bryan Litz who earns a portion of his living studying and educating shooters of all walks and trades have documented the altitude affect on muzzle velocity with scientifically defensible means and methods? And after having documented the relationship between altitude and MV, then include an algorithm into ballistics programs to model the affect of altitude on MV for the benefit of the troops, or customers?
Small arms ballistics programs include algorithms for temperature, angle of fire, coriolis drift, wind speed, wind direction, spin drift & rifling twist rate, rifle cant, station pressure, humidity, and on and on. Each of these factors are proven, not with anecdotal evidence and old wives tales passed along over years and generations, but based on defensible science that can be repeated by any other qualified person employing the same scientific methods.
Why is there no MV correction based strictly on station altitude??? Logic will lead one to the obvious conclusion. Altitude in and of itself has no affect on MV.
BallisticsGuy
Well-Known Member
I guess it's time for me to go back up the hill with a chronograph and a Kestrel. I don't have gobs of time either but I'm happy enough to go out and have a good time shooting and gather some data.
One of you doesn't seem to want to arrive at an answer, happy to assume someone else had that on their list of things to do in the last century but provides no study abstract to support the assertion. The other already has their answer but its derivation from a tiny sample doesn't lend it to being applied generally so the former calls it an anecdote instead of what it is which is empirical experimentally derived evidence deserving of further investigation. It's deserving of investigation simply because the result was not null. The fact that data may not have been perfectly scientifically gathered only promotes the case for further testing so that the result can be verified or refuted.
A final thought, accusations of logical fallacy use are like accusations of misspellings and poor grammar. They're almost always accompanied by, if not surrounded by, the very thing they decry. This thread was no different.
One of you doesn't seem to want to arrive at an answer, happy to assume someone else had that on their list of things to do in the last century but provides no study abstract to support the assertion. The other already has their answer but its derivation from a tiny sample doesn't lend it to being applied generally so the former calls it an anecdote instead of what it is which is empirical experimentally derived evidence deserving of further investigation. It's deserving of investigation simply because the result was not null. The fact that data may not have been perfectly scientifically gathered only promotes the case for further testing so that the result can be verified or refuted.
A final thought, accusations of logical fallacy use are like accusations of misspellings and poor grammar. They're almost always accompanied by, if not surrounded by, the very thing they decry. This thread was no different.
