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#1 |
Senior Member
Join Date: June 17, 2004
Location: Somewhere south of the No
Posts: 3,824
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The Myth of Barrel Length and Velocity Loss
Best article I've seen on barrel length and velocity.I've always felt that 22" wasn't the best barrel length for my 30.06,but apparently it doesn't really matter.
http://www.guns.com/the-myth-of-barr...city-loss.html |
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#2 |
Senior Member
Join Date: August 17, 1999
Location: North Florida
Posts: 1,351
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It's not a myth: if you use a slow powder, it will burn longer while developing more velocity. So a long barrel can produce more velocity if you use a slower, but suitable powder.
This is easy to see in pistol loads: a fast powder will tend to have no, or reduced muzzle flash. A slow powder will generate a big ball of flame at the muzzle, because the powder is still burning after the bullet exits the barrel.
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#3 |
Senior Member
Join Date: January 8, 2001
Location: Forestburg, Montague Cnty, TX
Posts: 12,795
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Right, not a myth. So what I get from the article is that because Sharpe found velocity loss was an average of 12 fps instead of the 25 fps per inch most people thought and therefore velocity loss is a myth. I don't see how anybody could possibly reach that conclusion. The provided information just said it was less than expected, not that it was wrong or a myth. The title is misrepresentative. If anything, the documented loss proves velocity loss is a fact.
I think this article is a bit more informative. The purpose wasn't to document velocity loss from barrel shortening, but to see if accuracy was affected. They measured accuracy and also velocity. The barrel was cut down by 2" at a pop. The lost 350 fps over the course of 8" (an average of 43.75 fps per inch) and lost 55 fps per inch or more in the middle range. http://findarticles.com/p/articles/m.../ai_110470564/
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#4 |
Senior Member
Join Date: July 20, 2005
Location: Indiana
Posts: 10,610
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A variety of factors influence velocity and barrel length is just one of them. Powder burn rate, bullet weight, powder charge, and atmospheric conditions also play a role.
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#5 |
Senior Member
Join Date: June 15, 2008
Location: Georgia
Posts: 10,978
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If folks bother to do 5 minutes of research on google they can find lots of data to debunk most of the myths of barrel length and velocity. Barrel length does have an effect on velocity. Just not nearly as much as many old wives tales that keep getting repeated would have us believe.
I've done a lot of testing, and research and have foune that the most reliable indicator is to plan on somewhere between .5%-1% of velocity change for each inch barrel length changes. This means that if you are getting 3000 fps from a barrel, cutting it 1" shorter will change velocity somewhere between 15-30 fps. |
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#6 | |
Senior Member
Join Date: June 16, 2008
Location: Wyoming
Posts: 11,060
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It's not a myth. Velocity does change with barrel length. How much depends on the ammunition, caliber and gun.
Here is an example. My granddaughter did a science project showing something else but she needed to know what changes to velocity occurred. She started out with a 26 inch 308 barrel, and Remington factory 180 grn corlok bullets. The first column is barrel length the second is velocity (at 10 ft from muzzle.) Quote:
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#7 |
Senior Member
Join Date: August 12, 2009
Location: Athens, Georgia
Posts: 2,608
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That's my kind of science project!
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#8 | |
Senior Member
Join Date: June 15, 2008
Location: Georgia
Posts: 10,978
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Quote:
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#9 |
Senior Member
Join Date: March 3, 2011
Location: Vernon AZ
Posts: 1,195
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Interesting.
When I was a kid, the belief on a 22 lr was that the powder burned up in the first 22 inches of the barrel. The last 2 inches was to ensure that the bullet was stabilized and achieved its best accuracy. What effect does the shorter barrell have on inherent accuracy? |
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#10 | ||
Senior Member
Join Date: January 8, 2001
Location: Forestburg, Montague Cnty, TX
Posts: 12,795
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Quote:
Quote:
Basically, what you learned was a myth, at least in regard to rifled barrels. As long as there is enough rifling for the bullet to attain a proper twist rate and as long as the crown of the barrel is properly cut, barrel length won't affect accuracy. That isn't to say that a reduced velocity bullet won't destabilize somewhat at a distance closer to the rifle when it drops down from super sonic to sub sonic. That isn't an issue of barrel length, but of flight characteristics.
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"If you look through your scope and see your shoe, aim higher." -- said to me by my 11 year old daughter before going out for hogs 8/13/2011 My Hunting Videos https://www.youtube.com/user/HornHillRange |
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#11 |
Senior Member
Join Date: September 13, 2005
Posts: 4,712
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In one of my copies of the Speer manual they discuss factors such as barrel wear, maching tolerances, etc., that result in shooters getting velocities that vary greatly from published lab figures.
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#12 |
Senior Member
Join Date: October 5, 2009
Posts: 559
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It's all about physics. The perfect length barrel is one that is long enough that your powder finishes burning just as the bullet leaves it. If the powder burns before the projectile exits, friction slows it down. If the powder doesn't completely burn, anything left over is wasted.
Practicality dictates that you find a barrel length somewhere in the middle. |
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#13 |
Senior Member
Join Date: January 30, 2006
Posts: 1,433
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I am not a physicist, but as a matter of physics, velocity is affected by barrel length and several other factors including, but not limited to, cartridge powder capacity, powder charge weight, powder burn rate, bullet weight, bullet diameter, bullet shape, bore rifling, bore diameter, primer, primer depth, etc. Many of these effects cannot be accurately identified and measured by the vast majority of firearms owners/shooters.
Thank you TriumphGuy - I was busy typing GPE style.
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#14 | |
Staff
Join Date: September 25, 2008
Location: CONUS
Posts: 19,055
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Quote:
I did a similar test using four Para-Ordnance 1911s, with barrel lengths of 5", 4-1/4", 3-1/2" and 3". I fired multiple ammo types through each pistol over a chronograph and charted the results. The first problem (as others have found) was that with the chrony set 10 feet from the muzzle, once I got to shorter barrels I generated errors because too much burning detritus was being shot through the screens. So I had to move the chrony farther out. With that rectified, I found that different ammos lost differing percentages of velocity as the barrel length decreased. The results were clear -- shorter barrels in general result in lower velocities, but the decline is not linear and the powder selection does make a difference. I can only imagine that if I could see the difference in barrels ranging from 3" to 5" in length, it must be more pronounced with rifle-length tubes. |
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#15 | |
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Join Date: January 27, 2010
Location: Norfolk, VA
Posts: 2,905
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Quote:
The pressure inside the barrel is in units of force per area. Multiply that by the cross-sectional area of the bullet and you get the forward force acting on the bullet. The friction between the bullet and the barrel is a force that acts to slow the forward motion. Subtract the friction force from the forward force, and the net forward force accelerates the bullet (f=ma). In a nutshell, increasing the barrel length will give you a greater muzzle velocity until you reach a point where the decreasing pressure inside the barrel does not give enough forward force to overcome the rearward force from friction. At that point, the bullet stops accelerating and begins slowing down. |
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#16 |
Senior Member
Join Date: August 23, 2010
Location: US South
Posts: 857
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Well...The only barrel I cut back from 26" to 23" where I had chronoed both before and after velocities lost 23 FPSPI. That's pretty close to the 25 myth!
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#17 |
Senior Member
Join Date: March 3, 2011
Location: Vernon AZ
Posts: 1,195
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double could not get your referenced site to load. Not your problem but my computer is quirky.
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#18 | |
Staff
Join Date: March 11, 2006
Location: Upper US
Posts: 30,518
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Quote:
Velocity loss from shortening the barrel is not a linear constant. As this example clearly shows. With this load, certain reductions were much more significant than others. And that's the way it is with other calibers and loads. Which reductions result in the greatest loss, and which result in minimal loss varies with a number of factors, and can be different for each different combination of factors. As a general rule its fine to say there will be velocity loss, but trying to boil it down to an average and apply that to everything is, I believe, the wrong way to go about it.
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#19 |
Senior Member
Join Date: June 15, 2008
Location: Georgia
Posts: 10,978
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The 100 fps drop between 26" and 24" seems odd. All the other velocity losses are right where I'd expect them to be. Most guns have "sweet spot where velocity gains sort of peak. With a 308 that is usually somewhere between 20-24". Normlly going shorter results in larger and larger velocity loses as the barrel gets shorter. Going longer usually results in smaller and smaller gains as the barrel gets longer.
If you look at enough of these tests you see a pattern. The .5%-1% theory has shown to be pretty accurate with almost every test I've looked at with guns with barrels between 20-26". Other than the one cut between 26" and 24" it is pretty close here, as well as in the average velocity loss. Except for the difference between 24" and 26" this is exactly what I've seen in many, many other similar tests. Perhaps it was a fluke, or an incorrect chronograph reading, which is what I suspect. In fact, after looking at Remingtons website I'm not so sure about any of Kraigwy's numbers. They show a 180 gr corelokt bullet getting only 2620 fps from 308 in a 24" barrel. He is showing more than that from an 18" barrel. Those numbers seem more accurate for a 30-06 than a 308. http://remington.com/pages/news-and-...allistics.aspx |
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#20 | |
Staff
Join Date: March 11, 2006
Location: Upper US
Posts: 30,518
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Quote:
Every gun/ammo combination has a unique mix of factors. Some guns shoot some ammo faster than others in the same caliber, even using the same ammo. Now, while most fall within the normal average ranges, there are those that fall outside average, on both ends. I have seen 100fps difference in three guns of the same barrel length and caliber, shooting the same ammo. its not common, but it happens. If you get a gun that clocks 100fps faster than factory, cherish it. If you've got one that clocks 100fps slower, don't sweat it, just shoot it to its trajectory and enjoy it. Odds are it will still work for any job you would choose just fine.
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All else being equal (and it almost never is) bigger bullets tend to work better. |
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#21 | |
Senior Member
Join Date: June 15, 2008
Location: Georgia
Posts: 10,978
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Quote:
But not this. 2800 fps with a 180 gr bullet is a hot load in a 30-06. Remington factory 308 loads are not hot loaded. Some guns certainly shoot faster than others, but it is the rare gun that actually reaches published ballistics with most being slower. I've NEVER seen a gun shoot factory loads 200 fps faster than the published balliatics. I wouldn't be surprised to see one 100-150 fps. slower, while another actually matched the published numbers though. |
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#22 |
Senior Member
Join Date: June 25, 2008
Posts: 2,681
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26 2826
24 2722 104 22 2713 9 20 2677 36 18 2654 23 16 2552 102 Average change = 55 fps or 27.5 fps/inch As far as the cited article goes, a good experiment analyzes the data and then draws conclusions from it. Beware of articles that have an obvious point of view they want to propound, especially ones that don't cite their data. |
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#23 |
Staff
Join Date: March 11, 2006
Location: Upper US
Posts: 30,518
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2800fps 180gr is a hot load for a .30-06, from a 22" barrel! The given .308 speed was from a 26" barrel. Given the long barrel, and a fast gun, I don't see it as impossible. However its more believeable with a 150gr bullet, and if there is any error in the data, I would think it was giving the wrong bullet weight.
However, I am not doubting the data as presented. It is quite possible, if not within the usual averages. Again let me emphasize that published veliocities are only 100% representative of what the factory got with their test gun and ammo. And lots of times, they don't list the barrel length used for the test. Factory loads are a good guide for general velocities, but your individual gun(s) can vary widely. What this example shows us is, that some velocity loss happens when your shorten the barrel. How much change is not constant per inch in this test. In another test with different ammo and gun, it might be consistant per inch, or it might not be. Assuming velocity loss per inch is constant, for all guns and ammo is, in my opinion, an error.
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All else being equal (and it almost never is) bigger bullets tend to work better. |
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#24 |
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Join Date: July 11, 2005
Location: Manatee County, Florida
Posts: 1,982
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I observed a guy at our gun club shooting his 7mm MAG custom carbine. Barrel length was 20 inches. He produced a fire ball at the muzzle with every shot. Looked quite dangerous to me for hunting in the forest during a dry spell. So it goes.
Jack
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#25 | |
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Join Date: December 31, 1999
Location: Middle Georgia, USA
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