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Updated PICS: Long question for longterm
- Thread starter 308sako
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Re: Long question for longterm single rifle usage
An interesting concept, and although I've been reloading since the late '70s, I can't honestly say whether it will prove valid or not. I agree that being able to say, 'oh, with the weather report for tomorrow, I should take load 1A.2 (or whatever) to the range' would certainly simplify things. I suspect that it will take someone with a ballistics lab and a degree in that field to definitively state whether such a plan is practical.
One potential problem that I see is that since you would essentially be constantly switching between loads, even though they may differ by as little as 1/2 grain of powder, your zero would constantly be changing.
For me, I think it would be simpler to develop one load that works year-round for each bullet that I plan to shoot in a given rifle. That would both greatly reduce the 'Murphy factor,' and give me confidence in how that one load performs and my ability to hit what I aim at.
An interesting concept, and although I've been reloading since the late '70s, I can't honestly say whether it will prove valid or not. I agree that being able to say, 'oh, with the weather report for tomorrow, I should take load 1A.2 (or whatever) to the range' would certainly simplify things. I suspect that it will take someone with a ballistics lab and a degree in that field to definitively state whether such a plan is practical.
One potential problem that I see is that since you would essentially be constantly switching between loads, even though they may differ by as little as 1/2 grain of powder, your zero would constantly be changing.
For me, I think it would be simpler to develop one load that works year-round for each bullet that I plan to shoot in a given rifle. That would both greatly reduce the 'Murphy factor,' and give me confidence in how that one load performs and my ability to hit what I aim at.
Re: Long question for longterm single rifle usage
Most benchrest shooters have known to "tune" their loads at each match location. And sometimes durring the matches from morning to afternoon loads.
Most keep notebooks on temperature and barametric pressure and the new comer is density altitude. By recording the temp and DA and keeping a log of what shoots best under those conditions, I think you can obtain what you're looking for.
For 6 or 22 PPC I usually go to old military surplus IMR 8208. If that didn't work for the weather at the moment, I pulled out Hodgden 322 Extreme.
For 308 my rifle likes IMR 4895 and IMR 4064. But I'm working on data for RE-15
Good luck with your work.
Most benchrest shooters have known to "tune" their loads at each match location. And sometimes durring the matches from morning to afternoon loads.
Most keep notebooks on temperature and barametric pressure and the new comer is density altitude. By recording the temp and DA and keeping a log of what shoots best under those conditions, I think you can obtain what you're looking for.
For 6 or 22 PPC I usually go to old military surplus IMR 8208. If that didn't work for the weather at the moment, I pulled out Hodgden 322 Extreme.
For 308 my rifle likes IMR 4895 and IMR 4064. But I'm working on data for RE-15
Good luck with your work.
Re: Long question for longterm single rifle usage
I feel that its going to depend on WHAT you are doing with that rifle. If it's benchrest, then I think you may have a valid point.
If it's LR Hunting or target shooting, then I think you may be reading too much into it. Find a load your rifle likes then roll with it. If you have to adjust dope for the temp, then note it in your databook and remember it.
I have been chasing loads for the last couple of sessions. At some point you realize that you are not getting the enjoyment/practice from SHOOTING because you are too busy analyzing loads. Today I just grabbed what I had loaded along with the dope cards for it and left the chrony and other crap at home. It was a pretty enjoyable day with lots of ringing steel at 800+ yards.
I feel that its going to depend on WHAT you are doing with that rifle. If it's benchrest, then I think you may have a valid point.
If it's LR Hunting or target shooting, then I think you may be reading too much into it. Find a load your rifle likes then roll with it. If you have to adjust dope for the temp, then note it in your databook and remember it.
I have been chasing loads for the last couple of sessions. At some point you realize that you are not getting the enjoyment/practice from SHOOTING because you are too busy analyzing loads. Today I just grabbed what I had loaded along with the dope cards for it and left the chrony and other crap at home. It was a pretty enjoyable day with lots of ringing steel at 800+ yards.
Re: Long question for longterm single rifle usage
Chris Long wrote a great article on barrel shock wave theory at
http://www.the-long-family.com/shock%20wave%20theory%20summary%20explanation.pdf
He makes a case that BR guys have known for years...barrel harmonics are EVERYTHING. I doubt that your rifles "go in and out of tune because of environmental changes throughout the seasons" unless you have a wood stock that is in contact with your barrel and is reacting to external conditions. The issue lies with your ammo. As temperatures rise, the internal burn rates change and ultimately change your velocity. This, in turn, will react with the harmonics of your barrel due to the fact that the bullet is moving out of the barrel at different speeds. If you develop an accurate load at a given temperature, you are working within an accuracy node of the barrel. As the temperatures rise or fall, you may move out of the node. Dan Newberry discusses his theory of "scatter nodes" at http://optimalchargeweight.embarqspace.com/#/ocw-vs-ladder/4529811360
If you follow the theories, you can develop a load that is resilient to temperature. It may or may not be a "tack driver" at all temperatures, but will offer consistent groups throughout a given range. However, serious comp shooters develop different loads for different temperatures. They shoot test zero's throughout the day to see how their POI is behaving and adjust with the appropriate ammo. I'm not sure what your application is and how anal you want to get, but you can arrive at the same destination buy taking different routes. It all comes down to a measure of degrees (pun intented).
Chris Long wrote a great article on barrel shock wave theory at
http://www.the-long-family.com/shock%20wave%20theory%20summary%20explanation.pdf
He makes a case that BR guys have known for years...barrel harmonics are EVERYTHING. I doubt that your rifles "go in and out of tune because of environmental changes throughout the seasons" unless you have a wood stock that is in contact with your barrel and is reacting to external conditions. The issue lies with your ammo. As temperatures rise, the internal burn rates change and ultimately change your velocity. This, in turn, will react with the harmonics of your barrel due to the fact that the bullet is moving out of the barrel at different speeds. If you develop an accurate load at a given temperature, you are working within an accuracy node of the barrel. As the temperatures rise or fall, you may move out of the node. Dan Newberry discusses his theory of "scatter nodes" at http://optimalchargeweight.embarqspace.com/#/ocw-vs-ladder/4529811360
If you follow the theories, you can develop a load that is resilient to temperature. It may or may not be a "tack driver" at all temperatures, but will offer consistent groups throughout a given range. However, serious comp shooters develop different loads for different temperatures. They shoot test zero's throughout the day to see how their POI is behaving and adjust with the appropriate ammo. I'm not sure what your application is and how anal you want to get, but you can arrive at the same destination buy taking different routes. It all comes down to a measure of degrees (pun intented).
Re: Long question for longterm single rifle usage
On Dan Newberry's site, he has a link to OCW instructions. http://optimalchargeweight.embarqspace.com/#/ocw-instructions/4529817134
In the instructions, he gives direction which I think speaks right to your goals:
"14. Triangulate the groups. This means to connect all three shots in a triangular form, and determine the center of the group, and plot that point on the target. Measure this point's distance and direction from the bullseye, and record the information somewhere on the target. Do this for all of the targets. If you have a called flyer, you should discount that shot, or replace it in the group if you have an additional round loaded with that charge.
15. You will now look for the three groups which come the closest to hitting the same POI (point of impact) on the targets. The trend of the groups should be obvious, normally going from low and favoring one side, to high and favoring the other side. But along the progression, there should be a string of at least three groups that all hit the target in the same relative point.
16. After you have carefully measured group sizes and distances and directions from the bullseye, you will know which three groups come the closest to hitting the target in the same POI. You now choose the powder charge which represents the center of this string. For example, if 34.7, 35.0, and 35.3 grains all grouped about 1.5 inches high, and about 3/4 of an inch right of the bullseye, you would choose the 35.0 grain charge as your OCW (optimal charge weight). This charge will allow 34.7 and 35.3 grain charges to group right with it. This will be a very "pressure tolerant" or "resilient" load.
17. Remember, don't get "bowled over" by a tiny group which falls outside the OCW zone. You can tune any of the groups to be tiny with bullet seating depth changes. After you have determined the OCW, you may want to try seating the bullets deeper or longer in .010" increments to see where your particular rifle does its best. I have often found that OCW recipes are so reliable that seating depth alterations--especially for hunting cartridges--often don't seem necessary."
As he states, the most accurate load may not be the most pressure tolerant. Just a thought.
On Dan Newberry's site, he has a link to OCW instructions. http://optimalchargeweight.embarqspace.com/#/ocw-instructions/4529817134
In the instructions, he gives direction which I think speaks right to your goals:
"14. Triangulate the groups. This means to connect all three shots in a triangular form, and determine the center of the group, and plot that point on the target. Measure this point's distance and direction from the bullseye, and record the information somewhere on the target. Do this for all of the targets. If you have a called flyer, you should discount that shot, or replace it in the group if you have an additional round loaded with that charge.
15. You will now look for the three groups which come the closest to hitting the same POI (point of impact) on the targets. The trend of the groups should be obvious, normally going from low and favoring one side, to high and favoring the other side. But along the progression, there should be a string of at least three groups that all hit the target in the same relative point.
16. After you have carefully measured group sizes and distances and directions from the bullseye, you will know which three groups come the closest to hitting the target in the same POI. You now choose the powder charge which represents the center of this string. For example, if 34.7, 35.0, and 35.3 grains all grouped about 1.5 inches high, and about 3/4 of an inch right of the bullseye, you would choose the 35.0 grain charge as your OCW (optimal charge weight). This charge will allow 34.7 and 35.3 grain charges to group right with it. This will be a very "pressure tolerant" or "resilient" load.
17. Remember, don't get "bowled over" by a tiny group which falls outside the OCW zone. You can tune any of the groups to be tiny with bullet seating depth changes. After you have determined the OCW, you may want to try seating the bullets deeper or longer in .010" increments to see where your particular rifle does its best. I have often found that OCW recipes are so reliable that seating depth alterations--especially for hunting cartridges--often don't seem necessary."
As he states, the most accurate load may not be the most pressure tolerant. Just a thought.
Re: Long question for longterm single rifle usage
What you seem to be missing is that if you do a proper OCW workup,then the resulting load should be resillient to slight variations.
I have come across loads that are pretty dang close even when comparing charge weights that vary by .5-1 grain
What you seem to be missing is that if you do a proper OCW workup,then the resulting load should be resillient to slight variations.
I have come across loads that are pretty dang close even when comparing charge weights that vary by .5-1 grain
Re: Long question for longterm single rifle usage
Thanks...I think. I'm not sure if sniffing your dung is a good thing, but I will assume it is.
I think you are working a thought that can be approached from at least two different angles. You can develop a "one size fits all" load for different situations or you can employ a "tool box" approach by developing different loads for different occasions. All can be done with the one rifle goal. Hunters do this all the time by loading the correct weight bullet for the size of animal to be taken and at what range it will be taken.
Here is what the ladder test guys have to say...
http://www.6mmbr.com/laddertest.html
The 1000 yard method is not my point. The discussion on accuracy nodes is.
Another tool you will definitely want to use is JBM Ballistics (the link is currently broken). One of the important parameters in their program is temperature. Another tool that will further tweak your brain is Quickload at http://www.neconos.com/
Good luck and keep us updated on how is all works out.
Thanks...I think. I'm not sure if sniffing your dung is a good thing, but I will assume it is.
Here is what the ladder test guys have to say...
http://www.6mmbr.com/laddertest.html
The 1000 yard method is not my point. The discussion on accuracy nodes is.
Another tool you will definitely want to use is JBM Ballistics (the link is currently broken). One of the important parameters in their program is temperature. Another tool that will further tweak your brain is Quickload at http://www.neconos.com/
Good luck and keep us updated on how is all works out.
Re: Long question for longterm single rifle usage
Dave,
I think you're on the right track in thinking that varying the charge weight based on temp to achive the SAME velocity that your barrel likes is the key. HOW MUCH to vary the charge by at each temp point is the $69M question. I think the only way to do that is to shoot your load (doing a mini ladder test) over a chrono thoughout the year in our varying temp bands and find the load that replicates your desired MV at that temp.
For the rest of the group - would Quickload also get him close enough to giving him his answer if he just manipulates the temp and charge weight to give him the desired MV? I would think it would get him within a couple tenths and then he could shoot those over a chrono to re-verify. Just thinking out loud here....
Dave,
I think you're on the right track in thinking that varying the charge weight based on temp to achive the SAME velocity that your barrel likes is the key. HOW MUCH to vary the charge by at each temp point is the $69M question. I think the only way to do that is to shoot your load (doing a mini ladder test) over a chrono thoughout the year in our varying temp bands and find the load that replicates your desired MV at that temp.
For the rest of the group - would Quickload also get him close enough to giving him his answer if he just manipulates the temp and charge weight to give him the desired MV? I would think it would get him within a couple tenths and then he could shoot those over a chrono to re-verify. Just thinking out loud here....
Re: Long question for longterm single rifle usage
Another factor which hasn't been addressed is that if he is doing the volume of test shooting to develop a working data base for different temps, barrel erosion will become a factor at some point. This whole discussion may hit a point of diminishing return if uber-accuracy is the goal.
Another factor which hasn't been addressed is that if he is doing the volume of test shooting to develop a working data base for different temps, barrel erosion will become a factor at some point. This whole discussion may hit a point of diminishing return if uber-accuracy is the goal.
Re: Long question for longterm single rifle usage
Another consideration during extreme ambient temperature changes might be the barrel temperature itself. Substantially colder steel will be more brittle, theoretically stiffer.
Stiffer barrel means faster harmonic resonance, so your node and antinode placement along the barrel will change with temperature, given the same initial shock from powder ignition.
As I understand things, the whole point of adjusting powder charge is to generate a combination of barrel vibration pattern and bullet velocity such that the bullet exits the muzzle when the muzzle is at it's quietest (i.e. the vibration harmonic 'node' is at the muzzle). That way the bullet gets flipped off center as little as possible when it exits.
I believe the vibration pattern of the barrel is constant for any particular shot, powder type/load, and temperature combination. Placement of the nodes and antinodes along the barrel length stays the same. They are a function of the barrel steel length, diameter, temperature, material, and ignition shock speed (powder type). Not bullet velocity.
Ignition shock travels through steel much faster than bullet speed, so barrel vibration is set up just after the bullet starts to move. So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no? The velocity of the bullet then is just an artifact of the different powder charges that are really working to adjust the barrel harmonics, maybe.
So, a freezing cold barrel, say at -35 degrees, should be measurably more or less accurate than one that's become very hot from a high rate of fire, because it vibrates differently.
Difference in powder temperature obviously makes for greater or lesser ignition pressure, and therefore bullet velocity as well as vibration pattern. But maybe barrel temperature plays a greater role, depending on thickness and length of the barrel.
Just a late-night thought.
Another consideration during extreme ambient temperature changes might be the barrel temperature itself. Substantially colder steel will be more brittle, theoretically stiffer.
Stiffer barrel means faster harmonic resonance, so your node and antinode placement along the barrel will change with temperature, given the same initial shock from powder ignition.
As I understand things, the whole point of adjusting powder charge is to generate a combination of barrel vibration pattern and bullet velocity such that the bullet exits the muzzle when the muzzle is at it's quietest (i.e. the vibration harmonic 'node' is at the muzzle). That way the bullet gets flipped off center as little as possible when it exits.
I believe the vibration pattern of the barrel is constant for any particular shot, powder type/load, and temperature combination. Placement of the nodes and antinodes along the barrel length stays the same. They are a function of the barrel steel length, diameter, temperature, material, and ignition shock speed (powder type). Not bullet velocity.
Ignition shock travels through steel much faster than bullet speed, so barrel vibration is set up just after the bullet starts to move. So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no? The velocity of the bullet then is just an artifact of the different powder charges that are really working to adjust the barrel harmonics, maybe.
So, a freezing cold barrel, say at -35 degrees, should be measurably more or less accurate than one that's become very hot from a high rate of fire, because it vibrates differently.
Difference in powder temperature obviously makes for greater or lesser ignition pressure, and therefore bullet velocity as well as vibration pattern. But maybe barrel temperature plays a greater role, depending on thickness and length of the barrel.
Just a late-night thought.
Re: Long question for longterm single rifle usage
If you are going to use the same rifle / load you can use a chrono to ensure seasonal changes in temp / humidity are compensated for . once you have OCW then you should be able to use the ballistics calc like Quickload to change the parameters or use a chrono to keep in the fps range or Both .
Bill
ce <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BallCoeff.606</div><div class="ubbcode-body">Another consideration during extreme ambient temperature changes might be the barrel temperature itself. Substantially colder steel will be more brittle, theoretically stiffer.
Stiffer barrel means faster harmonic resonance, so your node and antinode placement along the barrel will change with temperature, given the same initial shock from powder ignition.
As I understand things, the whole point of adjusting powder charge is to generate a combination of barrel vibration pattern and bullet velocity such that the bullet exits the muzzle when the muzzle is at it's quietest (i.e. the vibration harmonic 'node' is at the muzzle). That way the bullet gets flipped off center as little as possible when it exits.
I believe the vibration pattern of the barrel is constant for any particular shot, powder type/load, and temperature combination. Placement of the nodes and antinodes along the barrel length stays the same. They are a function of the barrel steel length, diameter, temperature, material, and ignition shock speed (powder type). Not bullet velocity.
Ignition shock travels through steel much faster than bullet speed, so barrel vibration is set up just after the bullet starts to move. So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no? The velocity of the bullet then is just an artifact of the different powder charges that are really working to adjust the barrel harmonics, maybe.
So, a freezing cold barrel, say at -35 degrees, should be measurably more or less accurate than one that's become very hot from a high rate of fire, because it vibrates differently.
Difference in powder temperature obviously makes for greater or lesser ignition pressure, and therefore bullet velocity as well as vibration pattern. But maybe barrel temperature plays a greater role, depending on thickness and length of the barrel.
Just a late-night thought.
</div></div>
If you are going to use the same rifle / load you can use a chrono to ensure seasonal changes in temp / humidity are compensated for . once you have OCW then you should be able to use the ballistics calc like Quickload to change the parameters or use a chrono to keep in the fps range or Both .
Bill
ce <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BallCoeff.606</div><div class="ubbcode-body">Another consideration during extreme ambient temperature changes might be the barrel temperature itself. Substantially colder steel will be more brittle, theoretically stiffer.
Stiffer barrel means faster harmonic resonance, so your node and antinode placement along the barrel will change with temperature, given the same initial shock from powder ignition.
As I understand things, the whole point of adjusting powder charge is to generate a combination of barrel vibration pattern and bullet velocity such that the bullet exits the muzzle when the muzzle is at it's quietest (i.e. the vibration harmonic 'node' is at the muzzle). That way the bullet gets flipped off center as little as possible when it exits.
I believe the vibration pattern of the barrel is constant for any particular shot, powder type/load, and temperature combination. Placement of the nodes and antinodes along the barrel length stays the same. They are a function of the barrel steel length, diameter, temperature, material, and ignition shock speed (powder type). Not bullet velocity.
Ignition shock travels through steel much faster than bullet speed, so barrel vibration is set up just after the bullet starts to move. So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no? The velocity of the bullet then is just an artifact of the different powder charges that are really working to adjust the barrel harmonics, maybe.
So, a freezing cold barrel, say at -35 degrees, should be measurably more or less accurate than one that's become very hot from a high rate of fire, because it vibrates differently.
Difference in powder temperature obviously makes for greater or lesser ignition pressure, and therefore bullet velocity as well as vibration pattern. But maybe barrel temperature plays a greater role, depending on thickness and length of the barrel.
Just a late-night thought.
</div></div>
Re: Long question for longterm single rifle usage
No.
The reason I say so is the intent to engage in long term usage.
The development overhead alone, in terms of bore life degradation, would be incompatible with that long term goal.
Imagine you are a WWII soldier with a Garand and M2 ball ammo available, and th... th... that's all, folks. You'd use what you got, and spend a bit of time getting your dope between battles when weather changes were significant, or not. Probably not, as Uncle Sam takes a dim view of individual soldiers engaging in ammo testing.
A reasonably canny marksman is going to have a basic zero and some experience to be able to predict some ballpark estimates of what's going on out there at the receiving end when Ma Nature rolls the dice.
More than this is not really required. Its about the expectations, which ones are reasonable, and how best to remain reasonable with the least cost in wear and tear to all involved.
If you're looking to wage a winning BR campaign with such a strategy, move on; this post holds no useful information for you.
If you're looking for a practical strategy for practical marksmanship, I'd say you're on the flightpath, Pilgrim...
But then, I was always conceited...
Fact is, I've tried what you have in mind, and even gone beyond into the land of harmonic tuning. The key lesson relates directly to my comment about excessive throat life degradation. Doing the development properly simply takes too many shots off the barrel's reasonable life expecatation. The results are ephemeral, and even with the right loads on the shelf, you can guess wrong about which one to grab, and Ma Nature really gets her rocks off watching us mere mortals trying to outguess her.
Far better to stay with a known resource, and known deviations, than to try and add a cant to the playing field. The field can definitely be canted, but getting it right's the catch. Humans are known to fail with remarkable regularity when tilting at Ma Nature's windmill.
Greg
No.
The reason I say so is the intent to engage in long term usage.
The development overhead alone, in terms of bore life degradation, would be incompatible with that long term goal.
Imagine you are a WWII soldier with a Garand and M2 ball ammo available, and th... th... that's all, folks. You'd use what you got, and spend a bit of time getting your dope between battles when weather changes were significant, or not. Probably not, as Uncle Sam takes a dim view of individual soldiers engaging in ammo testing.
A reasonably canny marksman is going to have a basic zero and some experience to be able to predict some ballpark estimates of what's going on out there at the receiving end when Ma Nature rolls the dice.
More than this is not really required. Its about the expectations, which ones are reasonable, and how best to remain reasonable with the least cost in wear and tear to all involved.
If you're looking to wage a winning BR campaign with such a strategy, move on; this post holds no useful information for you.
If you're looking for a practical strategy for practical marksmanship, I'd say you're on the flightpath, Pilgrim...
But then, I was always conceited...
Fact is, I've tried what you have in mind, and even gone beyond into the land of harmonic tuning. The key lesson relates directly to my comment about excessive throat life degradation. Doing the development properly simply takes too many shots off the barrel's reasonable life expecatation. The results are ephemeral, and even with the right loads on the shelf, you can guess wrong about which one to grab, and Ma Nature really gets her rocks off watching us mere mortals trying to outguess her.
Far better to stay with a known resource, and known deviations, than to try and add a cant to the playing field. The field can definitely be canted, but getting it right's the catch. Humans are known to fail with remarkable regularity when tilting at Ma Nature's windmill.
Greg
Re: Long question for longterm single rifle usage
Greg:
You confirm my diminishing return statement. As one goes through the testing process, the throat erodes at a continuing rate. So in essence, one would have to know the rate of erosion and attempt to calculate that in as well...there's some math that will make you want a stiff drink. At the moment one finds the magic load combinations he may be ready to re-barrel his rifle and start all over again with the new barrel. Doesn't seem to be a great way to spend money.
BC:
My understanding of shock wave does not line up exactly with yours. You say, "So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no?" I believe the shock wave will be fairly consistent regardless of load. If you struck the barrel with a hammer with different force, I think the shock wave would respond similar because of the physics of the barrel (steel type, thickness, length, etc). I think the real answer is to assume that the shock wave is a constant and bullet velocity is the variable. As you increase or decrease the speed that the bullet travels down the barrel, it will move through the constant waves created by the ignition shock at differing rates. In his article on shock wave theory, Chris Long says, "In steel, the speed of sound is very close to 0.227 inches per microsecond, or about 18916 FPS. A wave will travel from the receiver to the muzzle in the barrel in about 0.12 mS. It can make around 4 or
5 round trips before the bullet leaves. Note that it does not matter how heavy the barrel is, or the profile, as the
wave travels at almost exactly the same speed in all cases."
DaveD:
I think we are having two discussions at once. We are discussing internal and external ballistics. Most of the thoughts have been focused on internal ballistics that have some pretty nargly math problems, but the bulk of your work will be done in the external ballistic world. Temperature has a dramatic affect on air density and will move your POI more than internal temperature issues. As you log your shooting sessions, you will begin to create a data base of prediction on how your bullet will behave. You will use this dope to adjust your POA in order to achieve your desired POI. The great thing is that your powder will be living in the same ambient temperature that your bullets will be flying through so internal and external ballistics will combine at the target. As you observe humidity, station pressure, altitude, density altitude and the like, you will be able to make accurate predictions. Temperature related powder burn rates will take care of themselves.
Hope this all helps.
Greg:
You confirm my diminishing return statement. As one goes through the testing process, the throat erodes at a continuing rate. So in essence, one would have to know the rate of erosion and attempt to calculate that in as well...there's some math that will make you want a stiff drink. At the moment one finds the magic load combinations he may be ready to re-barrel his rifle and start all over again with the new barrel. Doesn't seem to be a great way to spend money.
BC:
My understanding of shock wave does not line up exactly with yours. You say, "So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no?" I believe the shock wave will be fairly consistent regardless of load. If you struck the barrel with a hammer with different force, I think the shock wave would respond similar because of the physics of the barrel (steel type, thickness, length, etc). I think the real answer is to assume that the shock wave is a constant and bullet velocity is the variable. As you increase or decrease the speed that the bullet travels down the barrel, it will move through the constant waves created by the ignition shock at differing rates. In his article on shock wave theory, Chris Long says, "In steel, the speed of sound is very close to 0.227 inches per microsecond, or about 18916 FPS. A wave will travel from the receiver to the muzzle in the barrel in about 0.12 mS. It can make around 4 or
5 round trips before the bullet leaves. Note that it does not matter how heavy the barrel is, or the profile, as the
wave travels at almost exactly the same speed in all cases."
DaveD:
I think we are having two discussions at once. We are discussing internal and external ballistics. Most of the thoughts have been focused on internal ballistics that have some pretty nargly math problems, but the bulk of your work will be done in the external ballistic world. Temperature has a dramatic affect on air density and will move your POI more than internal temperature issues. As you log your shooting sessions, you will begin to create a data base of prediction on how your bullet will behave. You will use this dope to adjust your POA in order to achieve your desired POI. The great thing is that your powder will be living in the same ambient temperature that your bullets will be flying through so internal and external ballistics will combine at the target. As you observe humidity, station pressure, altitude, density altitude and the like, you will be able to make accurate predictions. Temperature related powder burn rates will take care of themselves.
Hope this all helps.
Re: Long question for longterm single rifle usage
I think that in field deployment, ie anything other than a bench or indoor tunnel, the enviromental conditions of DA and wind will eliminate any ability to tune a load to the conditions. Basicly I think the slight variables in any load for a certain set of conditions will be less of a variance that the actual conditions themselves.
I know im lazy. I shoot varget in the .308 year round and dont even start to make changes (comeup changes in the scope, not the load) until I see a 30degree swing or a couple thousand feet of difference in DA. Even then more of my success or failure comes into making the proper corrections and making a good trigger squeeze.
I think that in field deployment, ie anything other than a bench or indoor tunnel, the enviromental conditions of DA and wind will eliminate any ability to tune a load to the conditions. Basicly I think the slight variables in any load for a certain set of conditions will be less of a variance that the actual conditions themselves.
I know im lazy. I shoot varget in the .308 year round and dont even start to make changes (comeup changes in the scope, not the load) until I see a 30degree swing or a couple thousand feet of difference in DA. Even then more of my success or failure comes into making the proper corrections and making a good trigger squeeze.
Re: Long question for longterm single rifle usage
You gun seems to be a little like mine. 47.7 and 47.8 shoot great, 47.9 and it all falls apart.
You gun seems to be a little like mine. 47.7 and 47.8 shoot great, 47.9 and it all falls apart.
Re: Long question for longterm single rifle usage
Nice shooting DD! It looks like your new barrel is finally coming around. I should have talked you out of it while you were ready to throw it in the dumpster.
Nice shooting DD! It looks like your new barrel is finally coming around. I should have talked you out of it while you were ready to throw it in the dumpster.
Re: Long question for longterm single rifle usage
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DaveV</div><div class="ubbcode-body">Greg:
<...>
BC:
My understanding of shock wave does not line up exactly with yours. You say, "So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no?" I believe the shock wave will be fairly consistent regardless of load. If you struck the barrel with a hammer with different force, I think the shock wave would respond similar because of the physics of the barrel (steel type, thickness, length, etc). I think the real answer is to assume that the shock wave is a constant and bullet velocity is the variable. As you increase or decrease the speed that the bullet travels down the barrel, it will move through the constant waves created by the ignition shock at differing rates. In his article on shock wave theory, Chris Long says, "In steel, the speed of sound is very close to 0.227 inches per microsecond, or about 18916 FPS. A wave will travel from the receiver to the muzzle in the barrel in about 0.12 mS. It can make around 4 or
5 round trips before the bullet leaves. Note that it does not matter how heavy the barrel is, or the profile, as the
wave travels at almost exactly the same speed in all cases."
<...></div></div>
After a little more digging, it appears that a guy 'Al' who apparently used to engineer B83 nuclear warheads for a living has done some good recent finite element analysis on barrel vibration. (Not sure how it compares to Gerald Bull's work on gun barrels; haven't been able to find any)
From his website report, the primary initial shock that affects a bullet in a barrel is the bullet being engaged by the rifling and pushed down the barrel. The barrel ends up like a whip being snapped, but in a slightly circular motion by the inertia of the bullet acting on the barrel when it starts to be turned by the rifling. There were 6 different types or levels of harmonics, but only the first one seems important.
Experiments showed the bullet left the barrel at different times depending upon powder load and ignition pressure, but the circular whip-effect was a little more constant. So, if the bullet left the muzzle right when the muzzle came back from its whip-snap it got thrown back into POA. If its velocity was too slow or too fast, it got to the muzzle when the muzzle was snapping away from POA.
When the bullet gets to the muzzle it randomly flips out at any point out of 360 degrees, because the whip-snap is rotational. So, any barrel vibration-caused 3-shot group spread should be roughly triangular for the same powder charge.
Dave, you're correct that the frequency of a wave in a material, and the speed of a disturbance through it is a property of the material itself, not the amount of energy initially imparted to the system. Only amplitude will vary with a sharper shock, not the waves transverse or longitudinal velocity nor frequency and wavelength.
However, substantially varying barrel temperature does change it's material characteristics, making it more rigid. That will increase the wave speed and harmonic frequencies through the cantilevered barrel; whether those are caused initially or are residual after the bullet has left the barrel.
Increasing the thickness of a barrel (and decreasing its length) also makes it a lot stiffer, so that would have a similar timing effect to freezing the barrel. However, I doubt freezing would decrease the amount of whip-snap like a thicker barrel would, because a thicker barrel is a lot stronger with a lot more structural material there, and is not only just stiffer or more brittle.
Low powder temperature reduces ignition pressure and bullet speed, and at the same time as very cold barrel temperature increases vibration and shock wave speed. These effects add up, they don't cancel out.
So any mismatch of bullet speed and the 'sweet spot' of barrel vibration can only increase outside of a small optimal range of temperature. Inherent accuracy should decrease when you get far away from the ambient temperature that you've worked up a load for.
Finally, powder temperature will not 'take care of itself' because a bullet has lower muzzle velocity when cold powder ignites inside of freezing cartridges for lower pressures. Together with colder, heavier air (lower DA) that will really drop your POI if you don't do anything about it.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DaveV</div><div class="ubbcode-body">Greg:
<...>
BC:
My understanding of shock wave does not line up exactly with yours. You say, "So what you're really doing is adjusting the vibration pattern of the barrel by adjusting the ignition shock (force and speed) by different powder charges, no?" I believe the shock wave will be fairly consistent regardless of load. If you struck the barrel with a hammer with different force, I think the shock wave would respond similar because of the physics of the barrel (steel type, thickness, length, etc). I think the real answer is to assume that the shock wave is a constant and bullet velocity is the variable. As you increase or decrease the speed that the bullet travels down the barrel, it will move through the constant waves created by the ignition shock at differing rates. In his article on shock wave theory, Chris Long says, "In steel, the speed of sound is very close to 0.227 inches per microsecond, or about 18916 FPS. A wave will travel from the receiver to the muzzle in the barrel in about 0.12 mS. It can make around 4 or
5 round trips before the bullet leaves. Note that it does not matter how heavy the barrel is, or the profile, as the
wave travels at almost exactly the same speed in all cases."
<...></div></div>
After a little more digging, it appears that a guy 'Al' who apparently used to engineer B83 nuclear warheads for a living has done some good recent finite element analysis on barrel vibration. (Not sure how it compares to Gerald Bull's work on gun barrels; haven't been able to find any)
From his website report, the primary initial shock that affects a bullet in a barrel is the bullet being engaged by the rifling and pushed down the barrel. The barrel ends up like a whip being snapped, but in a slightly circular motion by the inertia of the bullet acting on the barrel when it starts to be turned by the rifling. There were 6 different types or levels of harmonics, but only the first one seems important.
Experiments showed the bullet left the barrel at different times depending upon powder load and ignition pressure, but the circular whip-effect was a little more constant. So, if the bullet left the muzzle right when the muzzle came back from its whip-snap it got thrown back into POA. If its velocity was too slow or too fast, it got to the muzzle when the muzzle was snapping away from POA.
When the bullet gets to the muzzle it randomly flips out at any point out of 360 degrees, because the whip-snap is rotational. So, any barrel vibration-caused 3-shot group spread should be roughly triangular for the same powder charge.
Dave, you're correct that the frequency of a wave in a material, and the speed of a disturbance through it is a property of the material itself, not the amount of energy initially imparted to the system. Only amplitude will vary with a sharper shock, not the waves transverse or longitudinal velocity nor frequency and wavelength.
However, substantially varying barrel temperature does change it's material characteristics, making it more rigid. That will increase the wave speed and harmonic frequencies through the cantilevered barrel; whether those are caused initially or are residual after the bullet has left the barrel.
Increasing the thickness of a barrel (and decreasing its length) also makes it a lot stiffer, so that would have a similar timing effect to freezing the barrel. However, I doubt freezing would decrease the amount of whip-snap like a thicker barrel would, because a thicker barrel is a lot stronger with a lot more structural material there, and is not only just stiffer or more brittle.
Low powder temperature reduces ignition pressure and bullet speed, and at the same time as very cold barrel temperature increases vibration and shock wave speed. These effects add up, they don't cancel out.
So any mismatch of bullet speed and the 'sweet spot' of barrel vibration can only increase outside of a small optimal range of temperature. Inherent accuracy should decrease when you get far away from the ambient temperature that you've worked up a load for.
Finally, powder temperature will not 'take care of itself' because a bullet has lower muzzle velocity when cold powder ignites inside of freezing cartridges for lower pressures. Together with colder, heavier air (lower DA) that will really drop your POI if you don't do anything about it.
