Keeping gun in tune.

R

russell m

Guest
6ppc using v 133 powder. Is it just humidity or is humidity & temp that affect tune? When the Humidity goes down I go up on the powder to keep my gun in tune? Is it that the powder kernals weigh less with lower humidity so I have to go up on the charge? Is it that the conditions change the harmonics of the barrel. Is it that the bullet travels through the air differently with the changes in conditions? russell m
 
russell m said:
6ppc using v 133 powder. Is it just humidity or is humidity & temp that affect tune? When the Humidity goes down I go up on the powder to keep my gun in tune? Is it that the powder kernals weigh less with lower humidity so I have to go up on the charge? Is it that the conditions change the harmonics of the barrel. Is it that the bullet travels through the air differently with the changes in conditions? russell m
Click to expand...


Russell,

Changes in air density is what makes our rifles go out of tune. If the bullets are exiting when the barrel is stopped at either the top or bottom of the swing, the rifle is in tune. If the atmosphere becomes less dense due to an increase in temperature, the bullet encounters less resistance as it travels down the bore and exits early before the barrel comes to a complete stop, in which case, we can either reduce the load or adjust the tuner to compensate. I think it's much simpler and easier to use a tuner. You NEVER have to change the load and can make your adjustments at the line.

Atmospheric density is the result of pressure altitude, temperature and to a far lesser degree, moisture content. Contrary to what many believe, dry air is heavier. Steam rises and it's 100 percent saturated.

So,, altitude, temp and humidity in that order. What do we mean by altitude? Range elevation above sea level. The Midland Shooters Association range is 2800 feet above sea level; that never changes so we can forget about it. Yes, slight variations in barametric pressure can change the pressure altitude but for all practical purposes, we can forget about it.

Temperature? This is the big one! It's actually the only thing you must concern yourself with. The temperature range from being perfectly in tune and being completely out is 20 degrees F.

Yep, if your rifle is perfectly in tune during the first match of the day when temperature is 70 it will be completely out of tune when the temp reaches 90 if you do nothing to compensate.

To keep the rifle in tune throughout the day, reduce the velocity 30 fps for each five degree increase in temp. With most powders, N133 being the classic example, this equates to one half click per five degrees. For example, let's say your rifle was in tune for the first match; temp was 70. Your Culver type measure was set on 54 clicks. When temp reaches 75 the proper click value is 53.5, for 80, 53, 75, 52.5 and for 90F, 52 clicks. Would you have ever believed it would take two full numbers to stay in tune with a twenty degree spread?

:mad: "Now wait a minute Beggs; are you telling me relative humidity has nothing to do with it?" Yep, that's right; very little, so little that for all practical purposes we can ignore it.

Relative humidity (RH) is expressed in percent of saturation at a given temperature. If RH is reported as 30%, temp 85 degrees, this means the air contains thirty percent of the moisture it is capable of holding at that temperature. If temp goes up, RH goes down and vice versa even though the amount of moisture in the air is exactly the same.

Some shooters say they adjust the powder charge by relative humidity; RH goes down, they go down on the load and vice versa insisting it is humidity that affects the rifle's tune when in fact it is the change in temperature that is actually responsible.

And BTW, you asked if changes in conditions affects barrel harmonics?" NO

Hope this helps

Later,

Gene Beggs
 
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To add to Gene's notes...

Moving two full numbers on the powder measure isn't always necessary. To follow that perscription is to chase exactly the same vibration high (or low)node in the the barrel. At +20 degrees, there is a vibration node coming up from behind that is nearly exactly where you started.

A different plan to manage bullet exit timing would be to go up for the first 10 degrees in temperature variation, then back down for the next 10 degrees -- essentially tuning the bullet exit to previous vibration harmonic high (or low) point. Details are of course gun/range/temp dependent -- but as a framework for proactively tuning it worth trying.
 
Good Point

CubCouper said:
To add to Gene's notes...

Moving two full numbers on the powder measure isn't always necessary. To follow that perscription is to chase exactly the same vibration high (or low)node in the the barrel. At +20 degrees, there is a vibration node coming up from behind that is nearly exactly where you started.

A different plan to manage bullet exit timing would be to go up for the first 10 degrees in temperature variation, then back down for the next 10 degrees -- essentially tuning the bullet exit to previous vibration harmonic high(or low) point. Details are of course gun/range/temp dependent -- but as a framework for proactively tuning it worth trying.
Click to expand...

Very good my friend; :D you are absolutely correct and your post shows you understand barrel vibrations very well.

I have avoided mentioning this before because I was afraid it would cause confusion. The same thing applies to tuners. You can never be more than a half turn out of tune. When tuning with the powder, you can never be more than .6 grains (one number on the Culver) out of tune. There is a post above by 'Goodgrouper' that gives an example of an extreme temp spread of fifty degrees. Obviously, in such a case it would not be necessary or wise to change the load in only one direction to stay with that temp swing.

It's hard to get your mind wrapped around some of this; isn't it? Hope you can help me find a simple, easy way to get this across to others. We redneck engineers from West Texas often have trouble communicating with the outside world. :eek::)

Come out when you can.

Later,

Gene Beggs
 
Quote:
Originally Posted by CubCouper
To add to Gene's notes...

Moving two full numbers on the powder measure isn't always necessary. To follow that perscription is to chase exactly the same vibration high (or low)node in the the barrel. At +20 degrees, there is a vibration node coming up from behind that is nearly exactly where you started.

A different plan to manage bullet exit timing would be to go up for the first 10 degrees in temperature variation, then back down for the next 10 degrees -- essentially tuning the bullet exit to previous vibration harmonic high(or low) point. Details are of course gun/range/temp dependent -- but as a framework for proactively tuning it worth trying.

Very good my friend; you are absolutely correct and your post shows you understand barrel vibrations very well.

I think I have it.

example, 70 degreesF= 52 clicks; temperature is rising to 90degreesF for the high.

LEARN to shoot and leave EVERYTHING alone.

CORRECT?
 
Gene Beggs said:
Russell,

Changes in air density makes our rifles to go out of tune. If the bullets are exiting when the barrel is stopped at either the top or bottom of the swing, the rifle is in tune. If the atmosphere becomes less dense due to an increase in temperature, the bullet encounters less resistance as it travels down the bore and exits early before the barrel comes to a complete stop, in which case, we can either reduce the load or adjust the tuner to compensate. I think it's much simpler and easier to use a tuner. You NEVER have to change the load and can make your adjustments at the line.

Atmospheric density is the result of pressure altitude, temperature and to a far lesser degree, moisture content. Contrary to what many believe, dry air is heavier. Steam rises and it's 100 percent saturated.

So,, altitude, temp and humidity in that order. What do we mean by altitude? Range elevation above sea level. The Midland Shooters Association range is 2800 feet above sea level; that never changes so we can forget about it. Yes, slight variations in barametric pressure can change the pressure altitude but for all practical purposes, we can forget about it.

Temperature? This is the big one! It's actually the only thing you must concern yourself with. The temperature range from being perfectly in tune and being completely out is 20 degrees F.

Yep, if your rifle is perfectly in tune during the first match of the day when temperature is 70 it will be completely out of tune when the temp reaches 90 if you do nothing to compensate.

To keep the rifle in tune throughout the day, reduce the velocity 30 fps for each five degree increase in temp. With most powders, N133 being the classic example, this equates to one half click per five degrees. For example, let's say your rifle was in tune for the first match; temp was 70. Your Culver type measure was set on 54 clicks. When temp reaches 75 the proper click value is 53.5, for 80, 53, 75, 52.5 and for 90F, 52 clicks. Would you have ever believed it would take two full numbers to stay in tune with a twenty degree spread?

:mad: "Now wait a minute Beggs; are you telling me relative humidity has nothing to do with it?" Yep, that's right; very little, so little that for all practical purposes we can ignore it.

Relative humidity (RH) is expressed in percent of saturation at a given temperature. If RH is reported as 30%, temp 85 degrees, this means the air contains thirty percent of the moisture it is capable of holding at that temperature. If temp goes up, RH goes down and vice versa even though the amount of moisture in the air is exactly the same.

Some shooters say they adjust the powder charge by relative humidity; RH goes down, they go down on the load and vice versa insisting it is humidity that affects the rifle's tune when in fact it is the change in temperature that is actually responsible.

And BTW, you asked if changes in conditions affects barrel harmonics?" NO

Hope this helps

Later,

Gene Beggs
Click to expand...

Gene,
I am curious if the change in tune correlates with the Mach number of the bullet or is it just coincidence that both are affected by temp.

James
 
Wait

What if you are loading in an air conditioned trailer at say 75 deg. and it's 90 outside. Your gun is outside with the barrel getting longer with the heat and it does. how do you put it all together. I think the same applies, it's the barrel lenght and air you have to contend with. Maybe I'm all wet, I'm new at this.
Bob
 
Bob Dodd said:
What if you are loading in an air conditioned trailer at say 75 deg. and it's 90 outside. Your gun is outside with the barrel getting longer with the heat and it does. how do you put it all together. I think the same applies, it's the barrel lenght and air you have to contend with. Maybe I'm all wet, I'm new at this.
Bob
Click to expand...

Hi Bob

You? New at this ? :eek: Yeah, right, :rolleyes:

You were a master of all this before I ever got involved in benchrest. But I like your sense of humor. :D

My feeling is that it doesn't matter whether or not you load in an air conditioned trailer. The thing that matters is the outside temperature and its affect on air density at the firing line.

The test group on the sighter will tell you whether or not the rifle is in tune. Make all tuner adjustments in reference to outside air temperature. If tuning with the powder charge, the same thing applies. If the rifle shows a full amount of vertical on the sighter the charge can either be increased or decreased .6 grains to bring the rifle in tune.

Later,

Gene Beggs
 
Gene

I agree that tuners work--but I disagree with you on the premise on which they work. Loading in an air conditioned trailer effects the powder moisture content and temperature--which is what effects tune. In my experience it is not the air in the bore or the DA of that air in the bore--that gets blown out of the bore long before the bullet ever touches it.

From my experimentation with tuning using powder charges and tuning using a tuner we are trying to adjust so that the bullet is exiting on the negative slope of the vibration curve so that we get some self compensation for velocity differences. Chapter 4 of Vaughn's book had some information that Jack Jackson provided based on shooting the "curve".

I have done that many times and it works whether by adjusting powder charge or tuner. Also, I have quite a bit of experience loading in an air conditioned trailer and I quit doing that as there was no temperature and humidity control--the unit just kept sucking the water out of the air and as it did--the same weight and volume (what we can measure on our little scales) the powder charge got "hotter".

Jim
 
Jim Borden said:
I agree that tuners work--but I disagree with you on the premise on which they work. Loading in an air conditioned trailer effects the powder moisture content and temperature--which is what effects tune. In my experience it is not the air in the bore or the DA of that air in the bore--that gets blown out of the bore long before the bullet ever touches it.

From my experimentation with tuning using powder charges and tuning using a tuner we are trying to adjust so that the bullet is exiting on the negative slope of the vibration curve so that we get some self compensation for velocity differences. Chapter 4 of Vaughn's book had some information that Jack Jackson provided based on shooting the "curve".

I have done that many times and it works whether by adjusting powder charge or tuner. Also, I have quite a bit of experience loading in an air conditioned trailer and I quit doing that as there was no temperature and humidity control--the unit just kept sucking the water out of the air and as it did--the same weight and volume (what we can measure on our little scales) the powder charge got "hotter".

Jim
Click to expand...


Jim, thanks for joining the conversation. I wish you and I could spend some time together, one on one. You are a very smart man and well educated. I, on the other hand, am lacking in formal education but have a keen understanding of physics, mechanics and aerodynamics. I can sometimes see things that someone like you will overlook. In my previous career this happened quite often.

You stated above, "I agree that tuners work--but I disagree with you on the premise on which they work."

You also said, "In my experience it is not the air in the bore or the DA of that air in the bore--that gets blown out of the bore long before the bullet ever touches it."
:eek: This is where you are overlooking something very important, so important that if you do not understand it, any further discussion of tuning is pointless. Let me explain.

Your comment, "that air in the bore--that gets blown out long before the bullet ever touches it" reveals to me that you think the bullet does not even 'touch the air' until it emerges from the muzzle. This is not true. The weight of the atmosphere rests against the nose of the bullet as it sits motionless in the breech.

Think back to your days in class where you learned about barametric pressure. There you learned that the weight of the atmosphere at sea level on a standard day causes a column of mercury (and that stuff's heavy) to rise 29.92 inches. That is what your bullet must overcome in order to exit the muzzle. The heavier the atmosphere the more resistance the bullet encounters as it travels down the bore; hence, greater elapsed time.

As the weight of the atmosphere decreases due to decreases in pressure and increases in temperature, the bullet encounters less resistance as it travels down the bore; hence, less elapsed time. That is why our rifles go out of tune.

Yes, I understand why airconditioned loading areas affect both the weight and burning rate of gun powder. That is why it is so hard to keep the rifle in tune with the load. With a tuner, all that becomes irrevelant. The tuner is very much like a focusing ring on a scope. Regardless of conditions, we focus our scope for the best sight picture. We do the same thing to the group with a tuner. Regardless of conditions, the test group on the sighter tells us whether or not the rifle is 'in tune/in focus.' We adjust the tuner until we get the smallest groups. :D Pretty simple; huh? That's exactly the way it works and we don't have to go through a long drawn out procedure to locate the 'one and only magic sweet spot' (there is no such thing.) We can NEVER be more than a half turn out of tune under ANY circumstances.

This winter when it gets miserably cold up there in the north, get on a nice jet aircraft and come on down here to Midland/Odessa, Texas and we will have some good times out at the tunnel. Won't cost you a dime other than your travel expenses. I look forward to seeing you. :D

Later,

Gene Beggs
 
Ok

Gene and Jim.
You are both right, your just going about it from 2 differant directions. I saw the effects of loading in a trailer years ago. You most times turn the air off at night and the humidity in the trailer goes up all night, as it does outside, only more so. The next mourning when you start loading it's normaly not warm enough to run the air until 11 or so. Thay's 3 to 4 matches, and must be addessed on the powder drop or the tuner. I've loaded my rounds the afternoon before a match, the next mourning it shot fine. If no load ajustment was made for the next match you'll think the gun broke. This doesn't mean that it can't be fixed by ajusting a tuner, the tuner just makes it easier to keep up by making the adjustment on the line. I've found that a 2 no more then 3 click adjustment on the powder drop will take care of it to. The same applies to someone loading outside in the mouning, eccept they aren't dring out the air and the change is much less detectable. The tuner changes the lenght of the air that the bullet must overcome more like how fast. Your doing the same thing adjusting the powder. We need to get in each others minds to really know what the other is thinking (saying). This should really screw up the thread and some minds.
Sorry
Bob Dodd
 
Those Higgs Bosun Particle Blues

All of the distinguished contributors above are doing an excellent job of explaining the practical aspects of tuning a rifle both with tuners and powder charges. They forget to mention the basic reason that changes in gun tune occur. Here in a nutshell is why: The Higgs Bosun particle is the theorized particle that transforms the energy in atoms into mass which makes the solar system, air, stainless steel, gunpowder, beer and us. It is the creator of life and as such has been nicknamed the "god particle". It is as yet undiscovered because the large hedron collider sprung a leak. Also there is a theory that for certain particles there are distant twin particles that will change if you screw with the first particle. These can be across the universe in distance but are probably closer. So if you mess with the Higgs Borun particles in your gun by twisting a tuner or changing a load you change the Higgs Bosun particles in your neighbor's gun and change their tune. Add to this the fact that merely observing a particle changes its properties.
Therefore the following is possibly true:
Your fellow benevolent shooters probably including your best friends are messing with the tune of your rifle. You are doing the same to them.
The act of adjusting a powder measure or twisting a tuner is bad enough. Don't look at them during the changing or after. That alone will change them more.
Those shooters consistently at the top of the heap do not obey the laws of particle physics. This observation has led to alternate explanations such as string, twine and rope theories.
I hope this clears up all this tuning discussion. Tim
 
Tim, I new you had it in you thanks for clearing everything up for me.:D:D
 
Tim, you're a riot looking for a place to happen ! Great sense of humor. Thanks for the good laugh. That's just what everyone needed.

Later,

Gene Beggs
 
Jim Borden said:
The "blow by" gases blow away that atmosphere long before bullet movement........

Jim
Click to expand...


Good morning Jim

Your input is greatly appreciated and I respect your right to disagree. As a member of the Benchrest Hall of Fame, designer and manufacturer of fine firearms and president of IBS, you have proven, you know what you're talking about. But like me and everyone else, you don't know it all. The most brilliant of men can learn something from the villiage idiot by listening, watching and remaining open minded. I'm not suggesting I'm the sharpest tool in the shed, far from it, but I do have a lot of knowledge and experience with supersonic, airborne projectiles.

You, as well as most others, are reluctant to believe that the miniscule amount of air in the barrel before firing could possibly affect internal ballistics and in-bore, elapsed time. This is because you are considering only the volume and weight of that air. What you are overlooking is the fact that this air must be compressed and pushed out of the barrel against the weight of the atmosphere.

The barrel is a long, sealed, cylinder. The bullet is a tight fitting piston that accellerates from zero to over mach 2.7 in the length of the barrel; it must compress and push out, against the weight of the atmosphere, that air in front of it before it can exit the muzzle. Can you imagine the compressive force, drag if you will, created by a piston that goes from zero to over two and a half times the speed of sound in a sealed tube of 22 to 24 inches in length? That's one helluva' compressor and you know how powerful compressed air can be.

Reduce the weight of the atmosphere and you reduce the amount of resistance the bullet experiences as it accellerates down the bore. Less resistance results in faster accelleration; hence, less in-bore elapsed time. The bullets begin to exit before the muzzle comes to a complete stop and the rifle goes out of tune.

Most people do not appreciate being proven wrong. I, on the other hand, love to be proven wrong because if I'm mistaken about something, I want to know the truth. During the past several years, Harold Vaughn, Dr. Jack Jackson, Brian Litz, and many others have proven me wrong a number of times.

Please consider the points I have made with an open mind and I think you will see what I'm talking about. I look forward to your response.

Later,

Gene Beggs
 
Gene

I am listening and open minded-------couple of counter points here on the theory you express. (and I certainly do not consider you to be the village idiot--you have gotten folks to look at tuners in a serious fashion and you have been open with your thoughts, conclusions and theories)

The bullet has blow by gases going by it as it starts its travel --that gas is going in excess of 4000 fps and it is blowing the atmosphere out of the barrel before the bullet has to push that air. If the rifle barrel was a closed tube--then yes lots of compression would be going on.

Have shot hundreds of tune curves with multiple rifles--the barrel vibrates in somewhat of a sine wave and the best tuning points are just past a peak or just before a valley. If you look at velocity versus barrel exit position as plotted by bullet impact change at 100 yards--that curve can be drawn.

temperature of ammunition and rifle effects velocity for given powder charge and water in the air effects the powder while we are loading it--which in turn effects velocity. the resultant velocity change then effects tune......

preloads have worked well for me as long as rifle is shooting well when I preload and then drastic temperature change is not experienced that would put gun out of tune (due to the velocity of bullet changing from that atmospheric temperature change)

Jim
 
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i aint as smart as either jim or gene, and have nowhere near the shooting experience of either.(ok my background is a combination of nuclear engineering and air cooled ICE's)
but........
someone has got to show me....pretend i moved to Missouri.

show me some data on blow by.

most of us are shooting at or near the lands.

more than one of us has put a bullet in the bore with a primer. stuck hard

my opinion is that the primer moves the bullet as powder burns and builds more pressure at the base of the bullet. as presure increases on the base of the bullet, the bullet expands AND moves forward. i do not believe there is any blow by in benchrest guns. too much pressure, too fine of a finish.
( i shoot a lot of cast bullets. we shoot at a lot less pressure, but with a much softer bullet. cast bullet shooting is about correct bullet size for the bore, correct hardness and correct lube. lots of commercial bullets are undersized, poor lubed and the results can be blow by. i have no blow by in my plain based 44 mag bullets, and great accuracy).

so we may start another thread or continue here, but i'd love to see some data on blowby.....(jim . not picking on you, asking a serious question).

mind clear and open....

thanks

mike in co
 
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