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Technical question

 
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  #8  
Old 12-31-2003, 11:39 PM
 
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Re: Technical question

AB

Are you assuming that the load for the shorter barrel must run a higher pressure in order to achieve the same velocity as the longer barrel, and therefore would have a higher exit pressure?

Just trying to understand how you arrive at your conclusions....
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  #9  
Old 12-31-2003, 11:57 PM
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Re: Technical question

ah.. brain fart. I cannot assume the shorter barrel will provide a higher pressure due to the parameters. It's really dependent on the powder type and amount used.

A fast burning powder will produce a peak pressure closer to the beginning of the barrel, then the pressure curve drops off rapidly (pressure vs bullet distance travelled down the barrel).

A slower powder will reach peak pressure further out and drops off gradually. Hence given the same barrel length the slower powder will produce a higher exit presure - this is where I tripped on that last comment.

AB
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  #10  
Old 01-01-2004, 12:08 AM
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Re: Technical question

I'm gonna show my ignorance here.
Please inlighten me. What is the deffinition of butting a bullet to sleep?
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  #11  
Old 01-01-2004, 12:15 AM
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Re: Technical question

baldeagle713,

As I've heard it put, it's when the wobble in a bullet settles down as it travels, has to do with gyroscopic stability, however I must agree with Chris in that I've never seen the effects when shooting at paper. I think we're splitting hairs here.

AB
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  #12  
Old 01-01-2004, 01:37 AM
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Re: Technical question

I would have to agree with the part about splitting hairs. The practical effect of this scenario is zero. The variables are so impossible to control that one would never be able to get the identical departure of bullet from barrel. In other words it can only happen on paper. BUT...

Since we are only playing with the theory of comparing a barrels ability to stabilize or up set the stability of a bullet then we need to bring up the topic of barrel harmonics.

A barrel, like any other pipe , has a resonant frequency. Like a wind chime. The major difference is that a wind chime tube hangs straight down and a gun barrel is largely horizontal and supported at only one end (when free floated).

When a bullet is shoved down the bore by the expanding gas the muzzle is lifted and the bore is straightened. Like when you begin to blow up an empty balloon. This causes an upward whipping motion that travels with the bullet down the muzzle. As the tail of the bullet leaves th muzzle the whip does a remarkable thing. Due to a gyroscopic phenomenon a force applied upward to the bullet will cause the bullets tail to kick sideways!!!

In practical shooting this is fine as long as the whip and kick are the same all the time. This is one major reason to free float a barrel.

To apply this to the origonal question though I would contend that the shorter barrel is stiffer and would whip and kick the bullet less and would thereby allow for a more steady departure of the bullet. A steady departure needs less time to stabilize.

BTW if you do the math you will find that the normal rifle bullet leaves the barrel at roughly (very roughly) 250,000 rpm. A .308 reaches 200 yds at .2 seconds and 300 at .3 seconds. How much quicker do you want it to stabilize? Really.
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  #13  
Old 01-01-2004, 06:25 AM
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Re: Technical question

Thank you!
Sleep = Stabilized ok makes sence now.
I would think that the Vapor trail off the bullet could give you a clue.
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  #14  
Old 01-01-2004, 08:51 AM
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Re: Technical question

Ghunting

You wrote;
Let's say you built two long range handguns with barrels from the same blank..... identical in every way except one.....the first handgun has a 14" barrel and the second has an 18" barrel......

DC---Lets look at something right here--4" length difference in barrels.

You wrote;
Then, let's say you built loads for each barrel identical in every way except one......

DC---The loads are the "same" in "BOTH/each" barrels.

You wrote;
The load for each barrel produced the same velocity in it's respective barrel......
DC-- If the "same" loads are used in BOTH length barrels, the longer barrel "should" produce "more" velocity.
For instance, if I shoot 100 grains of powder with a 200 gr bullet in one of my rifles and from a 30" barrel, the velocity "WILL" be slower then that "exact" same load in a 36" barrel. Same should hold true with your 4" longer barrel if you use the "SAME" load in each.

You wrote
in other words, both pistols shot the same bullet at the same velocity.....
DC---If you shoot the "SAME load in each, the longer barrel should produce "MORE" velocity which would be a better choice for downrange impacts.

You wrote
Now the question, assuming they both shot the same bullet at the same velocity.....would the added length of the second barrel have any effect on the trajectory of the bullet?
DC--- The added length should do better as per downrange impact and ballistics.

If in fact, the barrels are producing the exact "SAME" muzzle velocity, there would be NO difference to downrange impacts or drops.
Starting velocity is the key here. If both are the same to start with at point A, they will end up at Point B the same.
DC----I can relate this to the S&W 44Mags I had years ago.
One in a 4" and one in an 8". When I used the SAME load in both, the 8" barrel gave a bit more velocity which was a better hunting handgun for me.

Check your velocity over a good Chronograph and see what they are.
If the loads are the "SAME in both barrels, the longer one "should" give a higher velocity and would be a better choice for a hunting handgun.
You can get tooooooo long in barrel length to where there is more bullet drag produced and the added length of the barrel adds very little to the velocity.
I doubt if that's the case here.

Hope that helped.
DC [img]images/icons/smile.gif[/img]
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