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effect of barrel length on velocity?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 05:34
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How much effect does barrel length have on velocity?  Specifically, are hand gun rounds a lot faster, and therefore more potent, when used in a carbine?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 05:43
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A longer barrel gives the propellant more time to burn, therefore a greater velocity being achieved. That is normally the case, all things being equal. But all things are not equal.

Given a rifle barrel, speed increases by around 40-100 ft per sec for every inch added, but only up to a point, around 40 inches or so, then it would actually slow down.
 
I would imagine bullets loaded for pistols etc are loaded with a smaller charge, therefore the slowing down process could happen at a much shorter barrel length. What that length is, I cannot help you.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 06:21
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all depends in powder used, bullet used, and caliber. a .223 will be really close 20fps in a 24 or 18 inch barrel with a 55gr bullet. now a 338rum and a 300gr bullet will vary 200 fps or more in a 18 to 30 inch barrel.  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 08:24
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Originally posted by 8shots 8shots wrote:

A longer barrel gives the propellant more time to burn, therefore a greater velocity being achieved. That is normally the case, all things being equal. But all things are not equal.

Given a rifle barrel, speed increases by around 40-100 ft per sec for every inch added, but only up to a point, around 40 inches or so, then it would actually slow down.
 
I would imagine bullets loaded for pistols etc are loaded with a smaller charge, therefore the slowing down process could happen at a much shorter barrel length. What that length is, I cannot help you.

I would be VERY surprised to see a rifle round gain 100 FPS per inch added.  In cutting down many 308s and 300WMs, I see usually between 25-50FPS loss, depending on barrel. Custom barrels, for me at least,  lose a little less, factory lose a little more.

Good question about the carbines, I have only recently started playing with a 40 S&W AR with an 11" barrel, but haven't chronoed any loads yet.  If it gains, it ain't 25-50 FPS, I would guess.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 08:33
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from my reloads on a 500S&W the barrel length plays a roll in it from the snub to the 6 or what ever I have. My guess is 41gr of powder don't burn completely in ether just more so in the longer barrel. I'll see if I can dig up the test data I have on them.

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Bullberry barrels has tested their barrels with different calibers with 1" length drops. Here is a link to the test on the 17 HMR that held the highest velocity with a 19" barrel. Accuracy improved as the barrel was shortened. The lengths tested ranged from 22" down to 11"

http://www.bullberry.com/HMRdata.html
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 08:59
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When loading pistol ammunition for a rifle the best results are achieved by using slower powders in the rifle. When charging the ammunition differently for a rifle, is important not to mix the ammunition between weapons. Extreme care should be exercised not to fire the rifle specific shells in a handgun.
Some reloading manuals have tables that will list pistol and rifle loadings separate. Other publishers are too fear that there could be mix ups and only list the pistol loadings.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 09:12
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I recently had a new rifle built.  I had a obermyer barrel put on it and had it cut 19" from the recoil lug.

I worked up a load and after I found an accurate load I chronoed 40 rounds.  I was averaging 2641.  I was really shocked to see that kind of velocity, I figured mid 2500s is where I would be.  Initially I thought something must be wrong with my chrono.  But I just got back from a 4 day rifle class and my data matched up with my velocity.  My cousin shoots a 700 5r milspec with 24 inch barrel, we shoot virtually the same load.  All the way out to 1000 yards I was always needing less elevation than he was to make the same hits. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 09:17
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I think that the chamber cut also plays a role. A tight matchgrade chamber and barrel combo would chrono faster then a loose.... wait this sounds all wrong. But I'm sure you get the drift???
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 11:07
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Recently there have been several LE agencies that have switched over to a 18" barrel for their 308 sniper rifles Many have started wih a 26" barrel & cut 1" off at a time till they got down to the 18" mark which had the same & better accuracy as the longer barrels.I personally have found this to be true with my Rem 5r .308.
 
I just purchased another Rem SS 5r mil spec in 20" barrel,this came directly from Remington,cut & threaded with a cap to cover the threads.Point being Remington must be thinking that smaller is better.
 
On a side note ,best length for a .22lr is 16" as it runs out of powder at that point.
 


Edited by stickbow46 - May/11/2012 at 02:47
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 14:36
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 16:52
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Very good article,Thanks KB Excellent
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/10/2012 at 19:27
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Pistol rounds depend on the a lot on the rounds.  The .45acp does not gain a lot, the powder normally used is to fast.  A 9mm or .357 that likes a slower powder gains alot with a longer barrel.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2012 at 11:40
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2012 at 20:26
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Good sight Thanks Ilya Excellent
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