calling all LONG RANGE SHOOTING experts!

The reason I mention that a rifle that shoots small groups at short range but they won't maintain the same angular value at long range is simple physics and actual firing tests.

First off, muzzle velocity spread causes elevation errors. A 50 fps spread in muzzle velocity may cause only 1/10th inch vertical shot stringing at 100 yards. At 1000, vertical stringing can easily be 15 to 25 inches depending on the bullet's BC and muzzle velocity average.

Second, the subtle air movements cause bullets to move sideways and sometimes up or down. The more time a bullet's in the air, the more their trajectory gets altered by atmospheric conditions.

Third, when several bullets of the same make and model are fired at exactly the same muzzle velocity, they won't all have the same BC all the way to the target. The slight imbalance each one has makes them have slightly different drag values due to coning. This causes vertical shot stringing as their BC has a 1 to 2 percent spread; sometimes more.

Add 'em all up and the result is groups open up about 5 to 15% for each hundred yards past the first hundred, depending on the magnitude of all these factors. Note the group size at the muzzle is zero MOA; it gets bigger the further down range the bullet goes and settles down for its in-flight trajectory; no two of which are exactly the same.
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All of which is EXTERNAL ballistics.

None of those factors have anything to do with the rifle, itself.

Theoretically, if the rifle is precise enought to hold "X" minutes of angle accuracy, it will remain constant regardless of distance. This assumes zero wind, zero movement of the rifle when fired, and precisely the same ammo.

Never gonna happen, you might say. Absolutely correct. There will always be external influences to bullet flight, none of which are relative to the rifle being capable of "X" moa accuracy.

You refer to inconsistencies in the barrel.
Well, if that affects bullet flight, it's going to do it at 100 yards, the same as it's going to do it at 1000. Is it going to be more apparent at 1000- of course!
But it's still there (if it's there) at 100 yards...you just may not see it.

When you're referring to the accuracy POTENTIAL of a rifle, it's just that- potential. Variations in ammo, wind, and shooter error have absolutely nothing to do with it.

If it shoots 1/2 minute of angle at 100, it will still be 1/2 minute of angle at 1000. Anything affecting that is not the RIFLE, it's external influences. Some of you have that confused...

Rifles can shoot lousy because of uneven lug contact, crappy barrels, loose actions, the list goes on...these are the things that affect the inherent accuracy of the rifle, and determine that it's "X" moa.

This goes to the recent thread about a 300 yard warehouse that was used as a test facility for benchrest rifles...removing as many external influences as possible, so as to determine what works best for the rifle.

Bullet flight is linear unless affected by external influences.
 
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Talk is cheap.OP,one way to find out.Shoot.I'll be happy to see your successful targets.One thing is for sure,you won't do it if the knowledgable folks here talk you out of trying.
 
tobnpr states:
Theoretically, if the rifle is precise enought to hold "X" minutes of angle accuracy, it will remain constant regardless of distance. This assumes zero wind, zero movement of the rifle when fired, and precisely the same ammo.
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True, but there's no such thing as precisely the same ammo. Even a 1% spread in BC and a 10 fps spread in muzzle velocity (about the best us humans can make happen) will cause a 1/2 MOA or more vertical spread at 1000 yards. At 100 yards, the vertical spread's less than 1/10th MOA
 
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Bart, no one is trying to discredit that what you're saying affects accuracy. Everything you have mentioned does make sense, but your not making any claims about the RIFLE. If you are an expert on the barrel harmonics of remington 700s then by all means gives us some evidence as to why that will make more of a difference at 1000 yards as opposed to 100. I think everything you are saying is valid, you're just bringing up degrees of error in the wrong part of the system.
 
bpeezer, I'm no expert on barrel harmonics other that I know that the harmonics of a whipping/vibrating barrel are the least of which cause the bore axis at the muzzle to point at different places as the bullet exits. And as long as the bullet's barrel time from case mouth to out the muzzle is the same, the muzzle axis will be pointing at the same place anyway. And the harmonics of a given barrel are always the same, regardless of the load that's fired in it. Any barrel of the same metals Remington uses made to the same dimensions will have the same harmonics. So harmonics is not even part of this issue. Harmonics plays no part of barrel accuracy, but the barrel's fundamental vibrating/whipping frequency may; that's different than harmonics. But that's the same for a given barrel regardless of the load fired in it.

As the barrel is one part of the system that the bullet goes through, it plays a big part of reshaping the bullet as the round's fired. If it didn't, then bullets a few ten-thousandths bigger than groove diameter would shoot just as accurate as those a thousandth or more smaller. But bullets need to be a bit larger than groove diameter for best accuracy. Smaller ones get unevenly distorted and therefore have a wider range of BC's as well as being more unbalanced. So they're off to a bad start in their first inch of flight out the muzzle. That's why barrels can make otherwise very accurate bullets not shoot very straight.

How many folks have measured their factory barrel's groove diameter to the nearest ten-thousandth then done the same with their bullets? Most folks who do this learn their bullets are smaller than their barrel's groove diameter.
 
I agree with you about measuring the barrel and the bullets, and you just schooled me on barrel harmonics for sure :D
 
And the harmonics of a given barrel are always the same, regardless of the load that's fired in it.
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Ummm...Nope....

Why do you think that "Powder "A", that pushes bullet "B" to "X" fps could have different groupings/accuracy as compared to "Powder "C" that pushes the same bullet "B" to the identical velocity??

You said it-correctly- above. Barrel whip.

It's because of different burn characteristics/speed of different powders affecting the barrel harmonics. In both cases, the bullet can leave the barrel at exactly the same velocity, and exhibit different flight trajectories. It's called barrel harmonics...that is, unless all of us handloaders have been overthinking the process.

If what you are saying were true, all we would need to do is pick one powder, get the load for the velocity we're seeking, and be done with it.
 
tobnpr asks me:
Why do you think that "Powder "A", that pushes bullet "B" to "X" fps could have different groupings/accuracy as compared to "Powder "C" that pushes the same bullet "B" to the identical velocity?
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One reason's that one of the powders slams the bullet harder into the rifling; that distorts bullets more than those more gently pushed into the rifling. Ball powders are often known to lessen accuracy even though they shoot bullets out at the same speed as an extruded powder. Pressure tests have shown a higher spike in start-up pressure when a round loaded with ball powder is fired than with extruded powder. This was more or less proved years ago when either Townsend or Whelen did tests at an arsenal with the 173-gr. bullet used in Garands and M1903's. IMR4064, a slower powder than IMR4895, gave better accuracy than IMR4895 and bullets from each had the same muzzle velocity. Engineers at the arsenal agreed that it was the more gentler push that slower powder gave that bullet as it started into the rifling. But the powder had to be weighed; high speed metering didn't dump charges uniform enough, so they stuck with IMR4895.

Then there's the issue of different powders taking different amounts of time to get the bullet out the barrel....even with all bullets having the same velocity.

Some years ago, I asked a mechanical engineer whose speciaty was how things vibrated, to write me a program to calculate the fundamental frequency barrels vibrate at. So he did and it allows to put in barrel diameters at different points for both a two and three taper barrel.

I asked him about a given barrels whipping or vibrating frequency for different loads shot in it. He said the only difference was how much amplitude the vibration has but the frequency stays the same. He asked me if I though a guitar string would vibrate at different frequencies if it was plucked different ways. Same as a chime on your doorbell. Tap 'em or smack 'em with anything from a hot dog to a ball peen hammer; they vibrate at the same frequency regardless of how hard they get impacted by some outside force.

He now sells this software on his web site. It's about half way down this page:

http://www.vibrationdata.com/StructuralFE.htm
 
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I guess we have a different definition of what "harmonics" means...

I refer to it in the broad definition of the process of barrel "whip"...
And absolutely, speed of burn and the time it takes the bullet to leave the barrel does vary- and that's exactly my point. The muzzle is at a different point in space...

So, when you said the barrel harmonics aren't affected by the load, they most certainly are in that regard (which is how I think most people interpret barrel "harmonics").

I'll take your engineer friend's word for it that the "frequency" remains the same, but I believe that's irrelevant in terms of the end result- which is that the barrel reacts differently with varying loads and powders of different speeds.

I think we are in agreement, but are speaking different languages here..
 
uhhhhh....

If the frequency is the same, but the amplitude is different, it will change the outcome unless BOTH rounds are released at exact 0 in the sinusoidal curve depicting the the vibratory response of the barrel at the very tip.

Then there's the issue of different powders taking different amounts of time to get the bullet out the barrel....even with all bullets having the same velocity.
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This will mean that the bullets WILL NOT leave the barrel at the same point in the vibratory response of the barrel, so they won't leave the barrel at the same point in space with the same relative trajectory. (That is, unless the difference in time is EXACTLY one period of the sinusoid, which is a near impossibility.)

Even if the difference in the ammo gave a difference in time equal to one period, since the amplitude is not equal, the bullets will leave at a different point in space (unless they both leave at a time when the magnitude of the curve is 0).

This graph shows how the relative displacement of the tip of the barrel changes with respect to time. As you can imagine, at a different amplitude the barrel will reach different displacements, but with the same frequency it will oscillate at the same rate. (which makes sense, as that is physically described by properties of pendulums.)

cos-graph.gif

*note: this is not an actual sinusoid curve for a barrel, but a stock image showing a similar curve
 
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I'm not trying to argue about what you said, I just wanted to clear up some of the physics you cited. You were just explaining a phenomenon to tobnpr and I wanted to help you back it up with more facts!

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Thanks, Bart, for all of your heavily researched knowledge on the subject.
 
Folks wanting to see (and perhaps learn some interesting stuff) about barrel whipping and vibrating, check out these sites:

http://www.varmintal.com/amode.htm

http://www.varmintal.com/apres.htm

Looks to me like it's not a good idea to have bullets leave around the peak, or zero point, of the curve. Perfectly timed to do so and noting the small spread in barrel time and muzzle velocity, half of 'em will leave the last few microseconds of the up swing and the other half on the same time frame on the down swing.

As the barrel's whipping mostly in the vertical and there's always a small spread in how long it takes for the bullet to go from case mouth to out the muzzle, all bullets will leave in a small spread of barrel movement at the muzzle. This was a distinct advantage for the British Commonwealth fullbore long range rifle shooters. Their SMLE .303's arsenal ammo they had to use burning cordite had quite a spread in muzzle velocity. But at long range, they were very accurate. Seems the faster bullets (with shorter barrel times) left sooner in the upward whip of the barrel; slower ones later. This caused compensation such that the faster bullets that dropped less left at a lower muzzle angle than the slower ones leaving later at a higher angle. At the shorter ranges, they used Mauser 98 front locking actions which had much less flexing than the rear locking SMLE actions and they were more accurate there than the SMLE's.

A couple of the USA military service rifle teams' testing their M14NM's learned they also had a bit of the same type of compensation caused by the gas port being about mid point in the barrel. Gas escaping there bowed the barrel up at that point forcing the muzzle axis down and accuracy at 600 yards and beyond was improved for the same reasons the SMLE's had.
 
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That's exactly the theory behind OCW, referring to the shock wave.
I don't know a damn thing about frequency vibration, but it makes sense, instinctively...


When this wave is present at the muzzle, there is
naturally much turbulence and obturation of the
"roundness" of the bore at the muzzle. However, when
this main shock wave has reverberated back to the
chamber end, the muzzle is relatively stable. This
window of opportunity, according to Chris, is the best
time for the bullet to exit the muzzle. The barrel is
basically straight, and relatively calm.
 
Chris Long's OCW is interesting reading, but it's never been proved. Nobody's measured bullet vs shock wave position that I know of.

Note the shock wave he talks about travels through the barrel at the speed of sound in steel. It makes several back and forth trips between the front and back of the barrel while the bullets going down the bore. So the timing of that shock wave and the bullet's position is critical.

Whatever amount of bore enlargement caused by this ain't enough to let gas escape past the bullet. If there was, there would be gas-cutting erosion throughout the bore instead of just at the breech end. Every match barrel I've shot has always had the same amount of copper wash all the way around at the muzzle and they shot all sorts of loads as accurate as benchrest rifles. To me, that's evidence that the effect of "roundness" of the bore at the muzzle is insignificant.
 
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Looks to me like it's not a good idea to have bullets leave around the peak, or zero point, of the curve.
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My reference to the zero was for magnitude, not derivative :o At the zero magnitude there is, as might be expected, no displacement. However, at the peak (which you're right, would NOT be a good idea for the bullet to leave at the peak) there will be maximal displacement.
 
Did some calculations for a 30 caliber barrel blank that's 1.1 inch diameter and 26 inches long. Used a groove diameter of .305 inch to (very closely) approximate a rifled bore. Here's the fundamental frequency for both a stand alone barrel and a barrel fixed into a receiver:

Stand alone barrel, 299.5 Hz

Barrel fitted to receiver, 47.07 Hz
 
Very interesting results! Makes me wish there was an easy way to time how long it takes for each bullet to travel the length of the barrel.
 
bpeezer, to time that bullet's travel from case mouth to out the muzzle, one would first have to decide what event was time zero. Here's some options:

1. When the firing pin strikes the primer.

2. First movement of the bullet in the case mouth (this doesn't start when the primer goes off in most centerfire rifle cartridges).

3. When the base of the bullet clears the case mouth.
 
Did some calculations for a 30 caliber barrel blank that's 1.1 inch diameter and 26 inches long. Used a groove diameter of .305 inch to (very closely) approximate a rifled bore. Here's the fundamental frequency for both a stand alone barrel and a barrel fixed into a receiver:

Stand alone barrel, 299.5 Hz

Barrel fitted to receiver, 47.07 Hz
Click to expand...

It what way is that useful information?
 
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