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Old December 27, 2012, 09:22 PM   #1
blackhawk8
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Guns VS Loads

Is it true that no 2 guns are exactly the same. What makes Different guns like different loads even same calibre guns ? been thinking about this all evening.
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Old December 27, 2012, 09:38 PM   #2
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Thanks for asking. Too bad my answer is so poor.

The same reason no two cars are exactly the same.

In a revolver, no two chambers in the cylinder are exactly the same.

But the manufacturers try to make them as identical as they can, at reasonable cost.

If you want more detailed and specific information than my first line, you have opened up the wide, wonderful world of interior ballistics and the factors are nearly infinite.

Rifle barrels (even of identical dimensions and weight) vary in stiffness and the resonance of harmonic vibration (barrel whip) will be different. How the barrel is bedded makes a big difference, too. The tools that form the chambers wear as they are used and no two chambers are likely to be identical, though they will be close. Wear on the locking lugs of the bolt changes over time, even on the same gun.

Handguns may seem to be more identical, but only (my opinion) because their shorter sight radius makes it harder to detect the differences, especially when it comes down to analyzing the groups on target.

You have asked a good question. So good, in fact, that it has been a lifetime study for thousands of gunsmiths and ballisticians.

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Old December 27, 2012, 09:46 PM   #3
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^what Lost Sheep said.

Then you add in the human factors...
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Old December 27, 2012, 10:02 PM   #4
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Don't Fret

It's called mass production. If two were the same, the labor would rocket the price 3-5x.
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Old December 28, 2012, 12:46 PM   #5
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Facts are, not two guns with succesive serial numbers are dimensionally the same in the bore which is the part most critical to accuracy. There's a few 10/10000ths spread in bore, groove and chamber dimensions that make a difference. And sometimes the rifling twist ain't perfectly uniform across them.

The biggest difference between what folks get with a given rifle and ammo selection is how well they shoot it. A given rifle will produce different accuracy levels with the same ammo across dozens of people shooting it. They all don't hold it and fire it the same way for each shot. And they all use different standards for measuring accuracy.

All of which is why, in a test ran decades ago with a .308 Win. match rifle that shoots 1/4 moa all day long from a free recoil rest, produced test groups from almost 1/2 MOA to a whole full 2 MOA size 5-shot groups at 100 yards as shot by a couple dozen people shooting it from a bench with its fore end and stock toe resting on bags and held against their shoulder when fired.

Go figure this out.

Lost sheep, Rifle barrels of identical dimensions and weight are the same in stiffness and the resonance of harmonic vibration. If they were not, then all the mechanical engineering formulas used by professionals calculating fixed beam stiffness would be out of a job. The same dimension numbers used for a given metal's modulus of elasticity gives the same resonant frequency.
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Old December 28, 2012, 01:21 PM   #6
math teacher
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Bart you are assuming even distribution of the alloys that make up the barrel which doesn't happen in the real world. That an impurities randomly distributed throughout the barrel. All can have some effect on the harmonics of otherwise identical barrels.
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Old December 28, 2012, 01:30 PM   #7
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Math teacher, I know that. Which is why they tune the metal bars on a xylophone and tubes on a chime to a given frequency by grinding off tiny amounts of metal.

There's also variables across a given lot of primers, bullets, powder, cases, firing pin impact and everything else. Many are much larger than what there is across a bunch of otherwise identical rifle barrels. If there really was a noticable difference betwen barrels, then why would the 7 or 8 Hart barrels with the same dimensions I've worn out all shoot the same load recipie with different lots of bullets, powder, primers about 1/2 MOA at 600 yards? And why would a couple dozen rifles all with different barrel length, diameters, bore, groove and chamber dimensions all shoot the same lot of ammo into about 1/2 MOA at 600 yards?

What's the difference between a barrel's harmonic and its fundamental frequency? Which one effects accuracy the most?

What the fundamental frequency range most rifle barrels have when free at both ends and when screwed into an action fixed in the stock and the other end free?
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Old December 28, 2012, 01:54 PM   #8
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My poiint was that no two barrels can be truly identical on which we seem to agree. Your other points are well taken.
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Old December 28, 2012, 03:28 PM   #9
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math teacher, Lot of match shooters own their own reamers Here something on the Palma reamers

http://benchrest.com/archive/index.php/t-66956.html?

Here is one on Tony Boyers reamers for the 6ppc

http://benchrest.com/showthread.php?...Boyer-3-Reamer

I had 4 reamers and gauges for the 6ppc sold two still have 2 plus I own other reamers/gauges. I've got few rifles had both chambers cut from same reamer and throated the same.

Lots of ways to do things
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Old December 28, 2012, 05:58 PM   #10
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And further on Bart B's points, I have a standard recipe for 69gr match bullets in .223 using Varget and CCI primers. The load has worked in at least 5 different barrels (3 on my rifle, 2 on my dad's) plus is pretty similar to what any number of other shooters will be using if they are using 69gr match bullets. I can also replicate that performance with Alliant RL-15 and Remington primers.

So while I will agree no two are the same there are many recipes that are "known" factors in many calibers. It gives you a good place of reference to start if nothing else.
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Old December 28, 2012, 08:34 PM   #11
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Thanks, Math Teacher, for mentioning the points I would have brought up.
Quote:
Originally Posted by Bart B.
Lost sheep, Rifle barrels of identical dimensions and weight are the same in stiffness and the resonance of harmonic vibration. If they were not, then all the mechanical engineering formulas used by professionals calculating fixed beam stiffness would be out of a job. The same dimension numbers used for a given metal's modulus of elasticity gives the same resonant frequency.
Quote:
Originally Posted by Bart B.
Math teacher, I know that. Which is why they tune the metal bars on a xylophone and tubes on a chime to a given frequency by grinding off tiny amounts of metal.
Right. If all bars of metal of the same dimensions (and what is a barrel but a bar of metal with a hole down the center?) have the same resonant frequency, then they would not have to use a grinder to tune the bars of a xylophone.

A tiny difference in the position of the muzzle at the instant (I use the word "instant" advisedly) the bullet exits can make a huge difference in where the bullet hits the target. We are talking microseconds here.

Thanks for reading and for your comment, but on that one and only point, I disagree.

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Old December 30, 2012, 07:11 PM   #12
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Quote:
A tiny difference in the position of the muzzle at the instant (I use the word "instant" advisedly) the bullet exits can make a huge difference in where the bullet hits the target. We are talking microseconds here.
And a properly and precisely bedded action, stress free, proper and consistent torque on action screws with pillars... is the 800 pound gorilla here that no one's mentioned yet.

I think if the term "accuracy" with respect to our hobby were replaced with "consistency" it might create a light bulb moment for some shooters. As you noted, getting the bullet to exit the muzzle while it is at the exact same point in space at every shot is what we're seeking.

Found this, and it made my brain hurt....

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