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effect of barrel length on velocity?

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River Runner View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote River Runner Quote  Post ReplyReply Direct Link To This Post Topic: effect of barrel length on velocity?
    Posted: May/10/2012 at 05:34
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?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8shots Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 05:43

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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bigdaddy0381 Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 06:21
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.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rancid Coolaid Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 08:24
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bigdaddy0381 Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 08:33
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote 3_tens Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 08:43
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 3_tens Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 08:59
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote supertool73 Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 09:12
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. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8shots Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 09:17
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???
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stickbow46 Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 11:07
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kickboxer Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 14:36
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stickbow46 Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 16:52
Very good article,Thanks KB Excellent
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Post Options Post Options   Thanks (0) Thanks(0)   Quote silver Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2012 at 19:27
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: May/16/2012 at 11:40
Check this site out:


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Post Options Post Options   Thanks (0) Thanks(0)   Quote stickbow46 Quote  Post ReplyReply Direct Link To This Post Posted: May/16/2012 at 20:26
Good sight Thanks Ilya Excellent
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