why do longer barrelled guns shoot farther? - Science, Math and Philosophy Forum

Two Plus Two Forums Other Topics Science, Math, and Philosophy

why do longer barrelled guns shoot farther?

Post Reply Subscribe

...

Page 1 of 2

1 2

Page 1 of 2

1 2

01-08-2010 , 09:47 AM

Josh J

journeyman

Join Date: Jun 2009 Posts: 349

maybe they dont, but im under the impression that a longer barrelled gun will shoot farther and more accurately than a gun with a shorter barrel using the same calibre and style of bullet. its seems like the added friction would just slow down the bullet, and any added rifling effect that contributed to more spin would further slow it down and wouldnt seem to even add any more accuracy. please advise.

Quote

01-08-2010 , 10:13 AM

MortalWombat

Pooh-Bah

Join Date: Sep 2004 Posts: 5,125

Up to a point, a longer one will shoot farther (with more muzzle velocity) because of a couple of factors. One is that in a shorter barrel, not all of the powder may have burned by the time the bullet reaches the muzzle, so there is less energy behind the projectile. Another is that longer barrels give the propellant force more time to work on propelling the bullet. Both of these factors overcome any decreases caused by friction, up to a point. If you make a barrel long enough, friction will overcome the other two factors.

Quote

01-08-2010 , 01:41 PM

BCEagleAce

adept

Join Date: Apr 2008 Posts: 753

A longer barrell will generally have a greater influence on accuracy than projectile distance. The longer barrell causes more spin and keeps it along a guided trajectory longer, therefore causing it to leave the barrell with a more steady vector.

Quote

01-08-2010 , 02:41 PM

durkadurka33

Carpal \'Tunnel

Join Date: Apr 2008 Posts: 8,709

Longer barrel allows for more of the explosive force to be transferred to velocity (obv it also helps w/ accuracy too).

Quote

01-08-2010 , 05:51 PM

DDNK

veteran

Join Date: Dec 2008 Posts: 2,591

Longer barrel = more time for projectile to stabilize = better accuracy = longer accurate distance.

Quote

01-08-2010 , 06:08 PM

daryn

Carpal \'Tunnel

Join Date: Apr 2003 Posts: 26,912

impulse.

increase barrel length = increase time of contact --> increase velocity

Quote

01-08-2010 , 09:39 PM

Hardball47

Carpal \'Tunnel

Join Date: Feb 2008 Posts: 13,308

Quote:

Originally Posted by BCEagleAce

This is your answer.

Quote

01-09-2010 , 12:43 AM

daryn

Carpal \'Tunnel

Join Date: Apr 2003 Posts: 26,912

yeah, but also the thing about impulse.

Quote

01-09-2010 , 01:57 PM

Max Raker

Carpal \'Tunnel

Join Date: Apr 2005 Posts: 15,738

Quote:

Originally Posted by daryn

impulse.

increase barrel length = increase time of contact --> increase velocity

I don't know much about guns but I don't think this is true. Why would a bullet still be accelerating when it is about to come out of the barrel? I would think longer barreled guns shoot further because they supply more force to the bullet right after you pull the trigger. You can make a short barrel gun that shoots just as far but it would be so inaccurate that no gun company makes it.

Quote

01-09-2010 , 03:27 PM

#10

uDevil

Carpal \'Tunnel

Join Date: Jul 2003 Posts: 6,941

Quote:

Originally Posted by Max Raker

I know a little about guns. It is true.

The pressure of the gas from burning propellant in the barrel remains higher than atmospheric pressure until the bullet exits the barrel. When the bullet exits, the sudden relief of pressure in the barrel is the biggest part of the 'bang' you hear. It also represents some wasted energy. If you made the barrel longer, you'd transfer more of that energy into kinetic energy of the projectile.

IIRC, around the time of the first gulf war, Saddam Hussein was supposed to be trying to build superguns with really long barrels as an alternative to his scud missiles.

Last edited by uDevil; 01-09-2010 at 03:34 PM.

Quote

01-09-2010 , 03:42 PM

#11

daryn

Carpal \'Tunnel

Join Date: Apr 2003 Posts: 26,912

Quote:

Originally Posted by Max Raker

why wouldn't it be true? force is a function of the powder in the gun (oversimplified). so if you have the same gun other than barrel length, the same force is acting over a longer distance, more impulse, more delta p, more v, longer trajectory. QED

can you get me into harvard or what? at least introduce me to a few girls.

Quote

01-09-2010 , 04:17 PM

#12

Max Raker

Carpal \'Tunnel

Join Date: Apr 2005 Posts: 15,738

Quote:

Originally Posted by daryn

I don't see why the force isn't almost instantaneous.

Quote:

can you get me into harvard or what? at least introduce me to a few girls.

My GF is sick so I only am in boston if I have to be. You can probably do better than the Harvard women I can introduce you, mostly know physics/math grad students. I couldn't really help anybody get in. One year I was even a grad student rep on the admissions committee and i still had zero say.

Last edited by Max Raker; 01-09-2010 at 04:23 PM.

Quote

01-09-2010 , 04:19 PM

#13

Max Raker

Carpal \'Tunnel

Join Date: Apr 2005 Posts: 15,738

Quote:

Originally Posted by uDevil

Oh that maybe makes a difference. I wasn't thinking about any air pressure differences.

Quote

01-09-2010 , 04:28 PM

#14

Ohgod

journeyman

Join Date: Nov 2006 Posts: 204

Quote:

Originally Posted by Max Raker

Oh that maybe makes a difference. I wasn't thinking about any air pressure differences.

How else would any force be imparted to the bullet? Powder burns, produces lots of hot, high pressure gas. Pressure higher behind bullet than in front -> bullet accelerates. Longer barrel -> greater impulse imparted to bullet -> bullet goes further.

Quote

01-09-2010 , 04:34 PM

#15

Concerto

Pooh-Bah

Join Date: Aug 2009 Posts: 4,564

The longer the explosion is confined by the bullet, the more explosion energy is converted to kinetic energy of the bullet rather than being dissipated into the great outdoors.

Quote

01-09-2010 , 05:12 PM

#16

uDevil

Carpal \'Tunnel

Join Date: Jul 2003 Posts: 6,941

Quote:

Originally Posted by Max Raker

Oh that maybe makes a difference. I wasn't thinking about any air pressure differences.

It doesn't have to be air pressure. Rail guns use EM.

It seems like a lot of physics has been motivated by the desire to make better guns. Even the LHC is just a big gun. Why does the LHC have to be large?

Quote

01-09-2010 , 07:14 PM

#17

carlo

Pooh-Bah

Join Date: Apr 2004 Posts: 4,016

One thing might be that gravity acts upon the bullet earlier with a short barrel than with a long barrel. For the shooters can you compare a 30 caliber pistol with a 30 caliber rifle with the same powder charge in the shell? If you shot the pistol at the same angle as the rifle and somehow get a picture of it certainly gravity acts earlier on the pistol but I'm unsure as to this being the entire effect.

I guess the question is whether a 30 caliber bullet in a pistol receives the same amount of effective force as one in a rifle. Can the mathematics even answer this question?

Quote

01-09-2010 , 07:18 PM

#18

Borodog

Enemy of the State

Join Date: Jan 2004 Posts: 25,491

Wow@thisthread.com

Quote

01-09-2010 , 09:19 PM

#19

uDevil

Carpal \'Tunnel

Join Date: Jul 2003 Posts: 6,941

Quote:

Originally Posted by Borodog

Wow@thisthread.com

That's unhelpful. Even smart people can fail to understand simple ideas or to make connections that seem obvious. I just learned to properly tie my shoelaces yesterday (seriously).

Quote

01-09-2010 , 09:34 PM

#20

spadebidder

Actually Shows Proof

Join Date: Aug 2008 Posts: 7,905

Quote:

Originally Posted by Max Raker

I don't see why the force isn't almost instantaneous.

It is, but acceleration is not. Acceleration occurs for as long as the force is applied up until some opposing force like friction balances it. A barrel is not nearly long enough or frictious enough for that. The bullet accelerates the whole time it is in the barrel and the explosion still has lots of energy left even after exit, which you hear.

The points about stabilization and spin don't affect the exit velocity, but they do affect the distance the bullet will fly.

Quote

01-09-2010 , 09:40 PM

#21

uDevil

Carpal \'Tunnel

Join Date: Jul 2003 Posts: 6,941

Quote:

Originally Posted by carlo

No. Gravity acts on the projectile throughout it's motion, regardless of the length of the barrel or the angle. This is a pretty common misconception. Compare the pistol and rifle simultaneously firing horizontally- the bullets hit the ground at the same time.

Quote

01-09-2010 , 09:44 PM

#22

spadebidder

Actually Shows Proof

Join Date: Aug 2008 Posts: 7,905

Quote:

Originally Posted by uDevil

If you drop a pebble it also hits the ground at the same time. Obviously the horizontal speed and distance isn't changed by gravity. However, if you measure accurately enough, the longer barrel doesn't "drop" the bullet as soon as the pistol, so the pistol bullet will always hit the ground first assuming an even starting point for the bullets (firing pins even with each other, rather than end of barrels).

Quote

01-09-2010 , 10:10 PM

#23

uDevil

Carpal \'Tunnel

Join Date: Jul 2003 Posts: 6,941

Quote:

Originally Posted by spadebidder

...the longer barrel doesn't "drop" the bullet as soon as the pistol...

This doesn't have to be true. But being neither a ballistician nor a physicist, it's too fine a point for me to care about.

Quote

01-10-2010 , 12:17 AM

#24

daryn

Carpal \'Tunnel

Join Date: Apr 2003 Posts: 26,912

Quote:

Originally Posted by Max Raker

I don't see why the force isn't almost instantaneous.

it is almost instantaneous. that doesn't mean the time of contact isn't a larger number if the barrel is longer. so you're just saying it's negligible? it's not.

Quote:

Originally Posted by Max Raker

My GF is sick so I only am in boston if I have to be. You can probably do better than the Harvard women I can introduce you, mostly know physics/math grad students.

that's who i'm looking for!!

Quote

01-10-2010 , 01:18 AM

#25

jmark

Pooh-Bah

Join Date: Dec 2003 Posts: 3,790

Longer barrels are more accurate.

Proof:

If you are standing distance x from your target then a gun with length of x will be the most accurate.

QED

Quote

Page 1 of 2

First

1 2

Last

Post Reply Subscribe

...

Page 1 of 2

First

1 2

Last