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# Using chronograph data to determine the best load????

#43
12-29-2005, 09:15 AM
 Gold Member Join Date: Jan 2005 Location: Searcy, Arkansas Posts: 700
Re: Using chronograph data to determine the best load????

Eaglet

I'll second that notion of being pretty ignorant, myself that is [img]/ubbthreads/images/graemlins/wink.gif[/img] I have not been a practicing engineer for almost 10 years now, and oh how quickly you lose it!

As I said on my last post, I am not trying to be an authority on this subject. I could be wrong (probably am) but it is an interesting topic to discuss and apply some of that dusty unused physics grey matter to.

As far as "for every action there is an equal and opposite reaction" That is true and is an established law of physics. However, the larger the mass the more slowly it is put into motion. I'm sure you have noticed the recoil of a heavy rifle seems more like a hard push compared to the sharp "kick" of a very lightweight rifle of the same caliber. The foot pounds of "kick" are the same. The weight of the heavier rifle spreads that kick out over a longer time interval and the acceleration of the rifle is not as fast, so we get the perception that the heavier rifle kicks less. In reality the kick is the same (in energy). We therefore establish a practical example of how the larger the mass the more slowly it is put into motion by a given amount of energy. When a cartridge is fired, energy is transferred to the 200 grain bullet and the 10 pound rifle equally and in the same instant. However, it takes a longer time interval for the energy to over come the resting inertia of the 10 pound weight of the rifle than the 200 grain weight of the bullet. Therefore the acceleration of the bullet is much greater than the acceleration of the rifle. This gives the bullet time to exit the bore before any significant acceleration of the rifle has occured.

I will not argue that the recoil starts at the instant of ignition. What I do believe is that due to the mass of the rifle, the recoil is slow to build up. This gives the bullet time to exit the barrel before there is any significant movement. Notice I said significant in my original post as well, because yes the recoil starts instantaneously.

There are many other factors which can come into play regarding how we "hold" our rifle from shot to shot. Different pressure points or amounts of pressure can change the harmonics of barrel vibration etc. Vibration travels up and down the barrel (and action, and stock for that matter)much faster than the bullet. I would be inclined to believe that how firm we hold the rifle changes the effect of the vibrations, therefore the accuracy or POI could be effected.

Bart B, In response to your question on the double rifles. All I can say is I don't have a clue [img]/ubbthreads/images/graemlins/confused.gif[/img]

For that matter I may be clueless on this whole discussion and just not realize it. It would not be the first time [img]/ubbthreads/images/graemlins/crazy.gif[/img]
#44
12-29-2005, 09:17 AM
 Platinum Member Join Date: Jun 2001 Location: Potomac River Posts: 5,070
Re: Using chronograph data to determine the best load????

O.K. Here I am. You will be sorry!

The answer is over in SS7MM ‘s reply in the Ramshot thread. BJ verbally got most of it right. As a side note it is interesting how much incorrect information is posted on the internet concerning work and energy in what passes for reference material.

First and foremost for all of the engineers - this is not a mechanical system. It is a chemical system just like a car. Energy comes from the combustion process. How much energy is in the powder and how much is released and converted into mechanical energy depends on barrel length powder burn rate, bullet weight, barrel diameter etc. Being an engineer also, I failed in my first attempt to analyze the problem because I assumed it was a mechanical system.

OK us lets us proceed to answer the question of free recoil versus shoulder recoil versus a brick wall.

Without resorting to any specific powder and bullet combination we will just use some typical numbers.

A primer is struck and ignites the powder which burns and expands at a rate sufficient to occupy the barrel and push a bullet out of the barrel at 3000 fps. In doing this the expanding gas applies pressure (force = mass times acceleration) in all directions. Some is applied to the bullet which moves down the axis of the barrel and a mechanical reaction occurs in the opposite direction if the gun is free to move (free recoil). The gas expands at a velocity that is controlled by the resistance of the bullet to moving down the barrel. This is the central point everyone is overlooking. The rate of powder burn and gas production in the barrel and the velocity of its expansion is the same no matter if the gun is attached to an F4 fighter jet going Mach 2 or is in a vise on a brick wall or in the extreme situation it could be mounted firing backward on a rocket sled which is a very funny situation of bullet falling on the ground. In physics we use different frames of reference called inertial frames to analyze this type of problem. This involves an observer involved with the situation and an independent observer standing off to one side.

The amount of time it takes to get the bullet out of the barrel by the expanding gases is the nearly the same (I said nearly) in all cases because the powder burns at the same rate no matter if it is moving or still. So the velocity of the bullet as it exits the barrel is 3000 fps if a person was sitting on the end of the barrel.

If a person is on the ground watching the gun being fired from a jet plane then the velocity of the bullet is 3000fps PLUS the speed of the plane. The pilot sees the bullet depart at 3000fps.
If a person watches a gun mounted backwards on a rocket sled and the sled is traveling at 3000 fps when the gun is fired the bullet will simply falls straight to the ground. The person on the rocket sled see the bullet depart at 3000 fps.

For all of you unbelievers, the next time you go deer hunting and are riding around in the back of your buddie’s pickup truck try throwing your beer bottle backwards and see if the bottle actually flies backward or if it actually flies in the same direction the truck is moving. Which occurs depends on how fast the truck is going and how drunk you are.

At this point in time those of you who are too bored to read anything else and are still with me, will probably understand that the movement of the gun during the time the bullet is in the barrel affects the velocity that a third party observer will see. So now lets get to free recoil versus shoulder vs brick wall.

Brick wall. Gun cannot move so bullet velocity is controlled solely by powder combustion process and exits at exactly 3000fps as seen by both observers.

Free recoil. Bullet in relation to barrel exits at 3000fps but barrel is moving to the rear at 4 fps (Bart B’s number). Independent observer sees bullet at 2996 fps. How fast the barrel moves to the rear can be calculated with any of the recoil calculators available on line. The one I have bookmarked is

http://www.travellercentral.com/rules/ke.html

Chuck hawks has these number for pistols

http://www.chuckhawks.com/handgun_recoil_table.htm

Shoulder recoil. The shoulder is simply addition of weight to the weight of the gun so there is more mass to move backwards. How much weight depends on how many Christmas cookies you have been eating. The shoulder slows the rearward motion of the gun down from the free recoil speed of 4 fps to let us say 1 fps (Monkey Blaster excepted – no shoulders big enough to slow it down). Bullet leaves the barrel at 3000 fps in relationship to the barrel but an independent observer standing to one side sees the bullet come out at 3000 – 1 = 2999fps.

Hope y'all have some accurate chronographs. [img]/ubbthreads/images/graemlins/grin.gif[/img]
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The Smokin Fur Rifle Club
#45
12-29-2005, 10:59 AM
 Gold Member Join Date: Oct 2005 Location: Great Falls, MT Posts: 712
Re: Using chronograph data to determine the best load????

Gonhuntin: Now see what you started!!! [img]/ubbthreads/images/graemlins/shocked.gif[/img]

Gentlemen: I thought that after 40+ years of shooting and reloading I knew a little about those subjects. But I am beginning to realize that like a couple of others here have said, "I dont have a clue!" [img]/ubbthreads/images/graemlins/confused.gif[/img] I must say however that this has been one of the most enjoyable discussions I have ever read. Frankly, it doesn't matter to me who is right , wrong , or indifferent for that matter, I am fasinated! I must also note that all of you gentlemen have conducted yourselves in an exemplary manner and I find that with this level and depth of discussion that is quite refreshing. Now, for my purposes, I find that the OCW method combined with a chronograph works just fine (I like to LOOK like I know what I'm doing whether I do or not [img]/ubbthreads/images/graemlins/blush.gif[/img])
So please, carry on and continue with the theories and discussions, I am learning more with each post.
Happy New Year and Good Shooting!
Jim
__________________

Raptor Stalker by
Kirby Allen APS
#46
12-29-2005, 12:57 PM
 Platinum Member Join Date: Dec 2005 Posts: 2,483
Re: Using chronograph data to determine the best load????

RDM416, your comment: "A bullet traveling at 3000fps will take .000722 seconds to exit a 26" barrel." is interesting. A 3000 fps bullet moves 1 foot in .000333 seconds, 2 feet in .000667 seconds. And bullets accelerate from 0 to X fps out the barrel in a nonlinear way. My guess is your number is very close to exact (kudos to you!!). So, where'd you get this number from?
#47
12-29-2005, 02:16 PM
 Platinum Member Join Date: Feb 2005 Location: Nevada Posts: 2,782
Re: Using chronograph data to determine the best load????

Buffulobob,
I gotta question for you. When you typed this:
[ QUOTE ]
For all of you unbelievers, the next time you go deer hunting and are riding around in the back of your buddie’s pickup truck try throwing your beer bottle backwards and see if the bottle actually flies backward or if it actually flies in the same direction the truck is moving. Which occurs depends on how fast the truck is going and how drunk you are.

[/ QUOTE ]
Were you smiling, laughing or just busting up? Please respond! [img]/ubbthreads/images/graemlins/laugh.gif[/img] I was laughing so hard my family thought i had lost it! [img]/ubbthreads/images/graemlins/smile.gif[/img]

MT4XFore,
__________________
-----------------------------

-----------------------------
HEBREWS 13:8
Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!!

---> As promised, God Sent His Prophet to us!
#48
12-29-2005, 02:31 PM
 Posts: n/a
Re: Using chronograph data to determine the best load????

[ QUOTE ]
Gonhuntin: Now see what you started!!! [img]/ubbthreads/images/graemlins/shocked.gif[/img]

[/ QUOTE ]

You're welcome!!

Does anyone know where I can get a rocket sled??? I know a guy that I think could be talked into sitting on the back and firing a rifle so we can see proof of that bullet falling to the ground theory! Even if it doesn't work out, he won't screw up any more of my hunts!! [img]/ubbthreads/images/graemlins/grin.gif[/img]
#49
12-29-2005, 02:49 PM
 Platinum Member Join Date: Feb 2005 Location: Nevada Posts: 2,782
Re: Using chronograph data to determine the best load????

GonHuntin,
That's hilarious!
Poor Guy!
__________________
-----------------------------

-----------------------------
HEBREWS 13:8
Jesus Christ the same yesterday, and to day, and for ever.

Our Lord Jesus said that as it was in the days of Noah and
also as it was in the days of Lot so it shall be in the days...
It's happening again!!! God sent to us His prophet, and His Word
to this generation and we once more are rejecting it as was prophesied!!!

---> As promised, God Sent His Prophet to us!

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