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#6368328 - 07/13/16 06:20 PM A question for the experts
Texas Dan Online   content
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Registered: 07/28/08
Posts: 11237
What causes a given rifle to shoot better and produce tighter groups with certain brands and/or loads of ammo?
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#6368373 - 07/13/16 07:08 PM Re: A question for the experts [Re: Texas Dan]
Michael W. Offline
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Registered: 11/22/10
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Loc: Central Texas / Comal County


Harmonic balance. Thats why hand loading works so well. You can tune the balance.


This explains it better than I could. https://www.shootingsoftware.com/barrel.htm
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#6368405 - 07/13/16 07:34 PM Re: A question for the experts [Re: Texas Dan]
blackcoal Online   content
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Registered: 01/19/12
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Loc: 60 Mi North of DFW
^^^^ plus little fellows known as gremlins that attack barrels and bullets and powders and burning rates even to the point of how much the ammo has been transported. And don't forget good lady Mother Nature with temps and humidity and pressure of her own.
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#6368427 - 07/13/16 08:00 PM Re: A question for the experts [Re: Texas Dan]
ChadTRG42 Offline
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Registered: 09/16/09
Posts: 9397
Loc: Lewisville, TX
The Science of Ammunition- where do you start!!?? There's lots to discuss. Ask a more detail question, instead of such a broad range, and I'll help. In a nut shell, it boils down to the right powder and powder charge for the right bullet and caliber used.

I find it interesting when I hear a shooter say "my rifle doesn't like that bullet". Most of the time, the rifle doesn't like the load (i.e.- the powder and powder charge used) with that bullet. I have taken MANY rifles and dialed in a very accurate load with my custom ammo on a rifle with the same bullet that didn't shoot well in factory ammunition. The customer is usually surprised when I get it to shoot.

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#6368461 - 07/13/16 08:44 PM Re: A question for the experts [Re: Texas Dan]
RiverRider Offline
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Registered: 11/11/07
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I don't doubt that, but sometimes you DO find that a rifle really just does NOT like a particular bullet---for whatever reason.
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Originally Posted By: Cleric
God I am hating caliber threads more and more

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#6368462 - 07/13/16 08:45 PM Re: A question for the experts [Re: Texas Dan]
Texas Dan Online   content
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Registered: 07/28/08
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Do rifle manufacturers take such things into account when designing gun barrels? It would seem necessary to tout their "out of the box" accuracy.
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Spring, Texas

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#6368466 - 07/13/16 08:54 PM Re: A question for the experts [Re: Texas Dan]
RiverRider Offline
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Registered: 11/11/07
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Loc: Wise Co.
Other than rate-of-twist and the way the freebore is cut, generally NO. Ammo is designed to function well (hopefully) in guns the way they are made, not the other way around.
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Originally Posted By: Cleric
God I am hating caliber threads more and more

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#6368539 - 07/13/16 10:10 PM Re: A question for the experts [Re: Michael W.]
Mickey Moose Offline
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Registered: 02/05/12
Posts: 2558
Originally Posted By: Michael W.


Harmonic balance. Thats why hand loading works so well. You can tune the balance.


This explains it better than I could. https://www.shootingsoftware.com/barrel.htm

And...



-Mickey
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#6368901 - 07/14/16 10:24 AM Re: A question for the experts [Re: Texas Dan]
bside Offline
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Registered: 06/10/14
Posts: 314
Loc: DFW
shortest answer I can give:

The end of your barrel moves up and down in something that approximates a Sine curve during firing:



you want the bullet to exist the barrel at a peak so that you're not inducing an additional force vector on the bullet, not on the way up or down. You get to that peak by tweaking the amount of powder and the COAL (jump/jam) of the loaded round.

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#6369069 - 07/14/16 12:22 PM Re: A question for the experts [Re: Texas Dan]
Blanco Offline
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Registered: 12/29/10
Posts: 789
Loc: Ft.Worth
Something I find interesting is using Quick load to come up with a better load. I mistakenly thought that the load that was most efficient would be the most accurate. Such is just not the case. Some of my best shooting loads are in the 85-89% range. I know I should have known better...it can only predict based on the numbers.
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#6369427 - 07/14/16 05:22 PM Re: A question for the experts [Re: bside]
Texas Dan Online   content
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Registered: 07/28/08
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Originally Posted By: bside
shortest answer I can give:

The end of your barrel moves up and down in something that approximates a Sine curve during firing:



you want the bullet to exist the barrel at a peak so that you're not inducing an additional force vector on the bullet, not on the way up or down. You get to that peak by tweaking the amount of powder and the COAL (jump/jam) of the loaded round.


Your explanation has me a liitle confused. Would not the points at which the waveform crosses the zero axis be the point where you want the bullet to exit the barrel. Whatever the case, the diagram explains how barrel length and makeup, as well as other factors that impact bullet velocity (powder charge, bullet weight, rifling twist, and even the burn rate of the powder) all play a role.

Still, the most accurate rifle in the world, from a design perspective, is no more accurate than the capabilities of the one pulling the trigger. It's a fact wasted on those who somehow believe that even though they seldom practice, they are as accurate as their rifle.
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Spring, Texas

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#6369457 - 07/14/16 06:03 PM Re: A question for the experts [Re: Texas Dan]
RiverRider Offline
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Registered: 11/11/07
Posts: 6199
Loc: Wise Co.
Dan, you want the bullet to exit when the speed of motion is at a minimum, which is at the maximum and minimum values of deflection. Where you cross the x-axis, the speed of motion is maximum.

In fact, some say that you want the bullet to exit the muzzle as it is approaching the very top of the peak. The theory is that if your lowest velocity round (taking shot-to-shot variations into account) exits just as the muzzle reaches the top of its vibration pattern, then the other shots which are higher velocity will exit a tad bit sooner BEFORE the muzzle is at its zenith. This helps compensate for the minute differences in trajectory due to velocity differences. Benchresters have told me that when the rifle is tuned properly this results in minimal vertical spread at a particular range---but ONLY at that range. If the rifle's tuned up for 100 yards, then it won't shoot well at 200.
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Originally Posted By: Cleric
God I am hating caliber threads more and more

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#6369633 - 07/14/16 08:15 PM Re: A question for the experts [Re: RiverRider]
Texas Dan Online   content
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Registered: 07/28/08
Posts: 11237
Originally Posted By: RiverRider
Dan, you want the bullet to exit when the speed of motion is at a minimum, which is at the maximum and minimum values of deflection. Where you cross the x-axis, the speed of motion is maximum.

In fact, some say that you want the bullet to exit the muzzle as it is approaching the very top of the peak. The theory is that if your lowest velocity round (taking shot-to-shot variations into account) exits just as the muzzle reaches the top of its vibration pattern, then the other shots which are higher velocity will exit a tad bit sooner BEFORE the muzzle is at its zenith. This helps compensate for the minute differences in trajectory due to velocity differences. Benchresters have told me that when the rifle is tuned properly this results in minimal vertical spread at a particular range---but ONLY at that range. If the rifle's tuned up for 100 yards, then it won't shoot well at 200.


Thanks. This makes complete sense. In lay terms, you want the bullet to exit the barrel end when it is "still", which occurs at the peaks of the shockwaves that bounce back and forth along the barrel axis. This would produce a specific ballastic performance, meaning the rifle and scope could be set to the zeroing preferred by the shooter with that round.

It would be a matter of trial and error to determine what round will perform in this way with a given rifle.


Edited by Texas Dan (07/14/16 08:22 PM)
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#6369652 - 07/14/16 08:36 PM Re: A question for the experts [Re: blackcoal]
Bbear Offline
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Registered: 11/24/13
Posts: 596
Loc: West Texas
Originally Posted By: blackcoal
^^^^ plus little fellows known as gremlins that attack barrels and bullets and powders and burning rates even to the point of how much the ammo has been transported. And don't forget good lady Mother Nature with temps and humidity and pressure of her own.


And don't forget you have to hold your mouth right! hammer nuts
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#6369701 - 07/14/16 09:21 PM Re: A question for the experts [Re: Texas Dan]
bside Offline
Bird Dog

Registered: 06/10/14
Posts: 314
Loc: DFW
Originally Posted By: Texas Dan
Originally Posted By: bside
shortest answer I can give:

The end of your barrel moves up and down in something that approximates a Sine curve during firing:



you want the bullet to exist the barrel at a peak so that you're not inducing an additional force vector on the bullet, not on the way up or down. You get to that peak by tweaking the amount of powder and the COAL (jump/jam) of the loaded round.


Your explanation has me a liitle confused. Would not the points at which the waveform crosses the zero axis be the point where you want the bullet to exit the barrel. Whatever the case, the diagram explains how barrel length and makeup, as well as other factors that impact bullet velocity (powder charge, bullet weight, rifling twist, and even the burn rate of the powder) all play a role.

Still, the most accurate rifle in the world, from a design perspective, is no more accurate than the capabilities of the one pulling the trigger. It's a fact wasted on those who somehow believe that even though they seldom practice, they are as accurate as their rifle.


No, because the barrel *is moving* up/down at those points, you want a point at which it's not moving/moving as little as possible. Think of flicking a spinning top inducing wobble and causing the top to fall over earlier -- that's the type of force we're trying to avoid.

look at any slice of time on the graph, you want the least vertical dispersion possible for a given time (plus/minus a small window of each side)


Edited by bside (07/14/16 09:22 PM)

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