Bob Kingsbury
New member
was it in the cold side of the oven during stress relieve?
Why would a barrel need indexed
- Thread starter Bob Kingsbury
- Start date
Boyd Allen
Active member
I think that the theory goes like this.
Bores are not straight. Under the pressure of firing, the internal arc of the bore straightens slightly starting an oscillation at the muzzle in the plane of the arc. It is desirable that this oscillation be vertical to minimize the horizontal dispersion in groups.
There has been some testing that shows a difference in grouping depending on how a barrel is indexed.
Gene has given all of us who do not have a lathe an wonderful opportunity to play with what may turn out to be a significant accuracy variable. It would be interesting if those that have a reliable method of determining which way the internal curve(s) of the bore are pointing (at the muzzle) would gather data about where that curve is pointing when the barrel is indexed for peak accuracy. If it turns out that there is a dependable pattern to this, then barrels chambered in calibers not suitable for Gene's bushing could be indexed in a matter that is likely to produce the best results. Currently, there are some assumptions about what sort of indexing is desirable. I think that we are about to find out if these assumptions are correct.
Bores are not straight. Under the pressure of firing, the internal arc of the bore straightens slightly starting an oscillation at the muzzle in the plane of the arc. It is desirable that this oscillation be vertical to minimize the horizontal dispersion in groups.
There has been some testing that shows a difference in grouping depending on how a barrel is indexed.
Gene has given all of us who do not have a lathe an wonderful opportunity to play with what may turn out to be a significant accuracy variable. It would be interesting if those that have a reliable method of determining which way the internal curve(s) of the bore are pointing (at the muzzle) would gather data about where that curve is pointing when the barrel is indexed for peak accuracy. If it turns out that there is a dependable pattern to this, then barrels chambered in calibers not suitable for Gene's bushing could be indexed in a matter that is likely to produce the best results. Currently, there are some assumptions about what sort of indexing is desirable. I think that we are about to find out if these assumptions are correct.
B
Big Al
Guest
This Is what I think happen, from my observations of what happens.
Owners of the model 43 Ohler using strain gauges can if they choose to do so, will confirm that the use of a strain gage measures the expansion of the out side of the barrel to determine the pressure. As the bullet passes down the bore the pressure behind the bullet expands the bore until the bullet exits the bore. This is where the tiny whip in the barrel comes from. Because it starts at the rear end of the barrel the oscillation travel back to front and continues until dampened. The bore not being centered in the barrel causes a thick side and thin side. This wave pattern (it is believed) can be further controlled to some extent by moving the barrel around it's circumference in hopes of making this wave a help to improve groups.
It is to be noted this is my wild a$$ guess as to what is going on anyway.
Owners of the model 43 Ohler using strain gauges can if they choose to do so, will confirm that the use of a strain gage measures the expansion of the out side of the barrel to determine the pressure. As the bullet passes down the bore the pressure behind the bullet expands the bore until the bullet exits the bore. This is where the tiny whip in the barrel comes from. Because it starts at the rear end of the barrel the oscillation travel back to front and continues until dampened. The bore not being centered in the barrel causes a thick side and thin side. This wave pattern (it is believed) can be further controlled to some extent by moving the barrel around it's circumference in hopes of making this wave a help to improve groups.
It is to be noted this is my wild a$$ guess as to what is going on anyway.
P
pacecil
Guest
Why index?
Pressuring the barrel does not tend to straighten it out. This is something proposed by those who think a barrel would act like a Bourdon tube. The tube has to be flattened to make it straighten.
Barrels "whip" because of the moment imposed during recoil and because of the inertia forces between bullet and barrel as the bullet travels down a curved barrel. Pressure traveling down a barrel is not what is causing it to whip.
The curvature of the bore is something that can't be determined. The barrel weight will make the barrel droop in the vertical plane but the curvature in the bore as a result of machining may occur in any plane or in multiple planes. Weight applied to the end of a barrel will increase droop and normally this ends up causing most of the barrel curvature to be in the downward direction. There is evidence that barrels perform best when the bending lies in a particular plane - indexing is an attempt to find that plane.
Pressuring the barrel does not tend to straighten it out. This is something proposed by those who think a barrel would act like a Bourdon tube. The tube has to be flattened to make it straighten.
Barrels "whip" because of the moment imposed during recoil and because of the inertia forces between bullet and barrel as the bullet travels down a curved barrel. Pressure traveling down a barrel is not what is causing it to whip.
The curvature of the bore is something that can't be determined. The barrel weight will make the barrel droop in the vertical plane but the curvature in the bore as a result of machining may occur in any plane or in multiple planes. Weight applied to the end of a barrel will increase droop and normally this ends up causing most of the barrel curvature to be in the downward direction. There is evidence that barrels perform best when the bending lies in a particular plane - indexing is an attempt to find that plane.
B
Big Al
Guest
I think the vibrations starts in a sequence of events that takes place from the first metal to metal contact release starts. From the point of the trigger moves the sear, sear releases from the firing pin, the movement of the pin/strike of the primer. Primer ignition, pressure of the charge ignition, bullet jump from the case. Yes pressure expansion of the barrel. All of these are factors in the cause of vibration. If the barrel only whipped after the recoil event, then why try to control the muzzle? Is all the recoil only at the time of charge of the propellant ignition? Obviously these events are sequential.
Boyd Allen
Active member
There is ample evidence that people have been able to see the internal curvature of barrels for centuries.
As I understand it, Savage straightens their sporter weight barrels, sighting through the bore at a light box that has horizontal parallel lines on a white translucent background. Evidently the reflections of the lines inside the bore make it easier to see where the pressure should be applied. (I am not advocating barrel straightening.) Also, if chambering is done with the barrel through the headstock, with one of the two common setup methods, the muzzle will be off center from the centerline of the headstock. I have also been told, by a credible source, that one can simply look through the barrel at a light source, with an educated eye, and spot bore curvature.
There are a lot of little things that can detract form accuracy if they are not right. Greg Tannnel will tell you that the reason that he makes his firing pin tip bushings long enough to guide through the full stroke of the pin is that he had a problem rifle, that he tried everything on, that that finally stopped throwing an occasional flier when he made that change. I have told a few Benchrest shooters about a little shroud trick that helps when the threads are a little too loose. It works. The groups get smaller. Group size has been changed by trigger substitution.
The point is that fom the time that the trigger is pulled there is a lot going on, and it all seems to matter to one degree or another. I wish that the source of barrel vibration was from a single source. That would be so much easier.
As I understand it, Savage straightens their sporter weight barrels, sighting through the bore at a light box that has horizontal parallel lines on a white translucent background. Evidently the reflections of the lines inside the bore make it easier to see where the pressure should be applied. (I am not advocating barrel straightening.) Also, if chambering is done with the barrel through the headstock, with one of the two common setup methods, the muzzle will be off center from the centerline of the headstock. I have also been told, by a credible source, that one can simply look through the barrel at a light source, with an educated eye, and spot bore curvature.
There are a lot of little things that can detract form accuracy if they are not right. Greg Tannnel will tell you that the reason that he makes his firing pin tip bushings long enough to guide through the full stroke of the pin is that he had a problem rifle, that he tried everything on, that that finally stopped throwing an occasional flier when he made that change. I have told a few Benchrest shooters about a little shroud trick that helps when the threads are a little too loose. It works. The groups get smaller. Group size has been changed by trigger substitution.
The point is that fom the time that the trigger is pulled there is a lot going on, and it all seems to matter to one degree or another. I wish that the source of barrel vibration was from a single source. That would be so much easier.
Bob Kingsbury
New member
Having placed many barrels in the headstock and looked thru
them while they are turning, I would think the Kaliescope
picture could be put in use. Some way of focusing and gaging the light
might tell us where the curve is
them while they are turning, I would think the Kaliescope
picture could be put in use. Some way of focusing and gaging the light
might tell us where the curve is
V
Vibe
Guest
I think this assumption is incorrect. The tube does not have to be flattened, though being flattened does exaggerate the effect.
T
tim in tx
Guest
one thing gene is doing
granted there are a number of planes to this particluar type of curve ,indexing the vast majority of the curve with the most runout visually speaking which can be marked fairly easy with 2 people involved,and i am speaking of the actual bore exit angle not just where the muzzle is high. picture this ,a bullet whipping through a curve it will jerk the barrel/action/ stock sideways during the recoil if the vast majority of the curve runs sideways as the bullet goes through the barrel,when it the curve is indexed in a verticle fashion the gun is planted into the bags and or raises on the bags .i will take the verticle and tune it out one way or another. kinda reminds me of golf,just playing the slice.but i am sure many of you know that it can still be a hummer even if it is crooked. indexing just helps the crooked barrel fair better in the the overall tuning aspect ,tracking and poi repeatability. tim in tx
granted there are a number of planes to this particluar type of curve ,indexing the vast majority of the curve with the most runout visually speaking which can be marked fairly easy with 2 people involved,and i am speaking of the actual bore exit angle not just where the muzzle is high. picture this ,a bullet whipping through a curve it will jerk the barrel/action/ stock sideways during the recoil if the vast majority of the curve runs sideways as the bullet goes through the barrel,when it the curve is indexed in a verticle fashion the gun is planted into the bags and or raises on the bags .i will take the verticle and tune it out one way or another. kinda reminds me of golf,just playing the slice.but i am sure many of you know that it can still be a hummer even if it is crooked. indexing just helps the crooked barrel fair better in the the overall tuning aspect ,tracking and poi repeatability. tim in tx
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pacecil
Guest
Numbers!
As it seems in every case when we began to discuss most of the factors that affect accuracy, the actual magnitude of the factor is never mentioned. For example: an analysis (FEA) of the change in curvature as a barrel is pressured may show that it does occur....here's a typical number you will get for a heavy benchrest barrel, .000004. It does this because as a tube droops from weight it flattens slightly. Again if you look at the number describing how much it flattens you might see a number such as .0000005
Then there is that question of what number you might come up with as you attempt to measure curvature. Best estimate I have ever been able to get is that if you look through the barrel you might see curvature if it exceeds .002 - .003 in a foot. In other words you might see it in a 24" barrel if it's over about .005. Check and see how accurate deep hole drilling is expected to be. Bottom line here is that the best barrels probably are about .005 out of straight and may snake around through several planes. Indexing may be the only way to get a rough idea of how a barrel curves.
I think it has been pretty well shown that barrels vibrate when a force is applied to the barrel. The only significant forces result from the moment applied at recoil, and the inertia force between barrel and bullet. When you come up with numbers resulting from these forces (as Varmint AL has done) you would see these are the only significant numbers that are important. Firing pin fall, primer ignition, pressures rise, and bullet jump, all do create vibrations, it's just that these vibrations don't generate numbers that are significant.
The numbers that will really be important are the differences in group size you get as you index a barrel. Mike Ross determined what this was for rimfire in a machine rest. I believe Beggs may do something similar for centerfire
As it seems in every case when we began to discuss most of the factors that affect accuracy, the actual magnitude of the factor is never mentioned. For example: an analysis (FEA) of the change in curvature as a barrel is pressured may show that it does occur....here's a typical number you will get for a heavy benchrest barrel, .000004. It does this because as a tube droops from weight it flattens slightly. Again if you look at the number describing how much it flattens you might see a number such as .0000005
Then there is that question of what number you might come up with as you attempt to measure curvature. Best estimate I have ever been able to get is that if you look through the barrel you might see curvature if it exceeds .002 - .003 in a foot. In other words you might see it in a 24" barrel if it's over about .005. Check and see how accurate deep hole drilling is expected to be. Bottom line here is that the best barrels probably are about .005 out of straight and may snake around through several planes. Indexing may be the only way to get a rough idea of how a barrel curves.
I think it has been pretty well shown that barrels vibrate when a force is applied to the barrel. The only significant forces result from the moment applied at recoil, and the inertia force between barrel and bullet. When you come up with numbers resulting from these forces (as Varmint AL has done) you would see these are the only significant numbers that are important. Firing pin fall, primer ignition, pressures rise, and bullet jump, all do create vibrations, it's just that these vibrations don't generate numbers that are significant.
The numbers that will really be important are the differences in group size you get as you index a barrel. Mike Ross determined what this was for rimfire in a machine rest. I believe Beggs may do something similar for centerfire
V
Vibe
Guest
Were that true Pacecil, there would be no discernable change in a rail gun (which has all of said moment removed) with and without a tuner. Since there have been reports of (sometimes significant) changes, one can only conclude that your assumption that the pressure is not an important factor in barrel whip must be incorrect.
Boyd Allen
Active member
I knew a fellow who bought top grade match barrels as untapered blanks, and cut them in half to make two custom bolt action silhouette pistol barrels. He probably has more actual experience with just how far bores are off center in the middle than anyone that I can think of. Based on my recollection of that conversation, you might want to gather some actual data rather than project tolerances and calculate. Don't get me wrong, I have great respect for engineering, but the numbers he mentioned would seriously disappoint you if you expect something like .005. As to the significance of the smaller sources of barrel vibration, you need to see a little more in the way of before and after targets when some of these minor sources are fixed. Some of this stuff just can't be bench raced; you have to actually do it to understand it. Discounting actual experience sort of reminds me of that old story about it being mathematically impossible for a bumble bee to fly.
I've got to agree with Boyd on this one......
I've seen instances where something as small as changing a firing pin spring, changing to a different bolt shroud or using some sort of shimming device (tape, paper, shoe goo, bolt sleeves, adjustment screws, detent balls) to take up some slack........ even something as small as rotating the bolt shroud to always left or right of center with your thumb or applying thumb pressure to the bolt shroud can cause a gun to shoot measurably better.
BIG things like a bouncing firing pin, bolt handle or trigger touching the wrong thing, front action screw touching the bolt, scope base screw too long..... aren't really that big yet the vibrations produced will screw with accuracy.
I can think of 5 things to go wrong just with the firing pin that will cause a rifle not to agg........ without getting into the trigger/striker interface and all of the things that can be wrong with the trigger. These "little things" will most definitely mess with accuracy.
I've got barrels which can be screwed onto 3 different guns, a barrel that shoots lights out on one may be a real dog on another and while this may not be an indexing issue it's surely a vibration issue. By the same token, how many times has a junk barrel been re-set onto another action and been a real shooter?
As far as all this vibration stuff being insignificant, I think it's a pretty well established fact that one can sometimes switch powders or primers and work up a load to achieve a similar working velocity and see remarkable changes. I feel that one of the real "secrets" of tuning long range rifles is to try different primers. 5 loads worked up with same everything EXCEPT different primers, all set to same velocity, sometimes one or two of the primer brands will print groups that just jump out and smack you. "Minor" changes in pressure curve can well equate to MAJOR changes on target.
I don't know if Gene's idea of doubling the threads in a single joint for the purpose of indexing will turn out to be a major accuracy advance but as long as it's showing promise it's certainly worthy of pursuit IMO ...... and sink or swim Gene's having fun and we're enjoying the vicarious ride..
And it's friggin' COOL!!!
Thanx Gene!
al
T
tim in tx
Guest
pacecil
i have done many barrels that if indicated on the ends have an aver runout of .002 in 2 inches of length,which is .001 off centerline per 2 inches,now multiply that by half the barrel length and you will get an average of what most barrels are running out providing it were constant which it is not but can get you in the ball park.if it is not a constant you will see it in the barrel,there are many types of curves in barrel i have seen,one is constant for 12 inches and then makes a wild curve and then comes back into the center and then is straight for the rest of the way out,or it may be slowly curving all the was through with no radical changes of the curve,every barrel has a differing curve and must be evaluated in the lathe first.let say i didnt worry about the curve and just cut the barrel on centers, now say you shoot a group over and over and you always drop one out straight down when you see a velocity change that is very small,what you do is to flip the barrel 180 degrees,can you see what will happen?the dropped bullet will now be pointed up and acted on by gravity and pull it in to the group instead of being pointed down from the barrel whip. this is one consideration that should be taken before any tuner is installed as well. tim in tx
i have done many barrels that if indicated on the ends have an aver runout of .002 in 2 inches of length,which is .001 off centerline per 2 inches,now multiply that by half the barrel length and you will get an average of what most barrels are running out providing it were constant which it is not but can get you in the ball park.if it is not a constant you will see it in the barrel,there are many types of curves in barrel i have seen,one is constant for 12 inches and then makes a wild curve and then comes back into the center and then is straight for the rest of the way out,or it may be slowly curving all the was through with no radical changes of the curve,every barrel has a differing curve and must be evaluated in the lathe first.let say i didnt worry about the curve and just cut the barrel on centers, now say you shoot a group over and over and you always drop one out straight down when you see a velocity change that is very small,what you do is to flip the barrel 180 degrees,can you see what will happen?the dropped bullet will now be pointed up and acted on by gravity and pull it in to the group instead of being pointed down from the barrel whip. this is one consideration that should be taken before any tuner is installed as well. tim in tx
Bob Kingsbury
New member
If you were to remove and re-install a barrel after 5 shots. Then
shoot 5 more in the same conditions. Wouldn't it be kinda rare that
the two groups be in the same place, or close enough to make a 3/10
for all 10. If I'm correct, Harold Vaughn was not happy with the
threaded barrel joint as its normally done. With the addition of an extra
part in threaded joint, it becomes more flexible and
can't be a good thing for accuracy. When it is determined
what position the barrel wants , wouldn't refitting to that
position , without the insert also change many things.?
shoot 5 more in the same conditions. Wouldn't it be kinda rare that
the two groups be in the same place, or close enough to make a 3/10
for all 10. If I'm correct, Harold Vaughn was not happy with the
threaded barrel joint as its normally done. With the addition of an extra
part in threaded joint, it becomes more flexible and
can't be a good thing for accuracy. When it is determined
what position the barrel wants , wouldn't refitting to that
position , without the insert also change many things.?
Maybe I'm missing something here. If you index the barrel 180 degrees so the bullet departs the barrel pointing up, the other 4 bullets will also depart the barrel pointed up resulting in the whole group printing higher. The lower velocity bullet would still impact lower..................................... gravity.
J
Jefferson
Guest
Can we link another website
the 6br.com in the rimfire section of the guns of the week, had an annie owner with a br50 stock do testing on indexing and explaining why calfee may be wrong on this, very interesting and does give a real world looks at why you index which was the question here, I do not know how to post the link,
it also quotes a gunsmith or 2 and their explanations, good article, wish I knew how to link it
Jeff
the 6br.com in the rimfire section of the guns of the week, had an annie owner with a br50 stock do testing on indexing and explaining why calfee may be wrong on this, very interesting and does give a real world looks at why you index which was the question here, I do not know how to post the link,
it also quotes a gunsmith or 2 and their explanations, good article, wish I knew how to link it
Jeff
Boyd Allen
Active member
Go to the page that you want to post a link to. Use your mouse to move the pointer onto the web address shown for that page at the top of the browser. Right click; choose copy; left click. In the message composition window (where you are composing your post), have the blinking cursor (where the next letter would apear if you were keyboarding)where you want the link to start. Put your pointer near the cursor; right click; choose paste; left click. Finish your post and post it. When you look at the post your link will be there.
http://www.6mmbr.com/gunweek080.html
http://www.6mmbr.com/gunweek080.html
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tim in tx
Guest
aj sir
look at it this way,if you are at the peak of the sine wave with the fast bullets but the slower bullets are exiting on the downside of the sinewave then flip that upside down and now the slow bullets are the only ones exiting the barrel on the upswing of the sinewave.so the slow bullets only are now pointing up on the exit aiming them higher then the fast bullets .hope that makes for a better explanation sir. tim in tx
look at it this way,if you are at the peak of the sine wave with the fast bullets but the slower bullets are exiting on the downside of the sinewave then flip that upside down and now the slow bullets are the only ones exiting the barrel on the upswing of the sinewave.so the slow bullets only are now pointing up on the exit aiming them higher then the fast bullets .hope that makes for a better explanation sir. tim in tx