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Velocity Vs barrel length

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Got thinking about this due to recent animated discussion on possible velocity Vs barrel length in a given calibre.
 
Need input from you experienced types, but it seems to me that if a certain barrel length allows complete combustion of the maximum safe powder charge then any additional length cannot increase velocity.  Would also think that in some cases faster powders could be used in shorter barrels to load up to the same max safe pressure to permit the same velocities in a longer barrel using slower burning powders.
 
Is this correct?  Only interested from an academic point of view.  Obviously different people may choose longer or shorter barrels based on their personal preferences.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 08:36
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Good question, I'm taggin' this so I can watch the replies also,  I would think it would be a matter of the amount of Volume needed for the gases the powder produces when burned and the speed at which any given powder is burning.
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You would be correct. Faster burning powders are of no practical use in longer barrels.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 09:12
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unfortunately this forum will not copy a HTML or matlab work sheets. its a work problem in a closed system. the amount of work that can be done by the propellant is fixed. the pressure vs. work curve aproaches a linear value within the first 1/3 of the pressure peak curve. while the bullet is still being accelerated, the derivative is significantly less than the first 1/3. the burning index (its not really a rate in the physics definition) or profile of the powder is a Poisson distribution with the degrees of freedom being the burning index. using thermodynmics it is easy to go from Pascals (psi) directly to lbs./force generated. thus a slower index would have more degrees of freedom in the distribution, and the peak pressure would be found further down the barrel (which gives a flatter longer peak). velocity at any given time or distance in the barrel is more a function of the bore dia. (surface area of the base of bullet) than barrel length (the relationship steelbenz mentions)-- but this is the variable most people choose. thus a comparison of energy delivered is done rather than energy delivered across an increase in bore dia. with the same amount of energy (powder charge.).

there will be a velocity increase up to about 30" of barrel length in any (and all) given system. the marginal gain (derivative) is what becomes the arguement. is the 2 ft/sec per inch gain a 22lr worth the additional length from 18 inch??

it has been known for a long time that if wanting a shorter barrel, go to a heavier bullet with a faster powder. the duplication in ballistic profile comes from adding mass back to the kinetic energy forumula.
 
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I should have added to burn all the powder AND achieve max pressures  - I think that would address the volume issue.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 09:28
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max pressure is a "measured"  absolute max the load can produce doesn't occur. very seldom is all the powder burned. powder manufactures even go to great length to measure the amount of unburned residue.
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Thanks Dale that was very interesting!
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 10:20
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Dale would faster powders allow the pressure curve to peak quicker allowing for similar velocities in a shorter barrel Vs slower propellants?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 11:12
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 12:42
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go to the Oehler web site and they have demo one can play with that shows the log decay of the pressure /per unit of length.

faster index powders contain a higher ratio of nitrates than slower index, thus more chemical energy per unit of weight. in order to do the same amount of work slower index powders total weight must be increased to accomodate, thus larger case capacity. (that avatar is really gross squeeze).

how much the velocity is increased in comparison to propellants is difficult to compare sense different wts. of powder are usually brought in. and an apples and oranges thing happens. in order to get higher velocities the pressure curve must not fall off to fast, initial peaking or it location doesn't solve the problem, because the peak pressure in both systems will only hit --say 20 Pascal. so the force vector over coming inertia is the same from the bullets observation point regardless of its location along the x-axis (distance from ignition).

slower index powders give more muzzle blast because there exit pressure is  higher as is there exit velocity.
using faster burning powders with heavier bullets in shorter barrels helps. but your also talking about linear systems with a very small margin. the system goes non-linear quickly.
only caught part of the animated discussion, but the newer powders prolong this curve so by "peaking sooner" so under the old definition system they would be said to be quicker, when in fact they are providing a more "sustained" acceleration vector, and from this definition system they actually could be termed "slower".
The historical discussions about powders are rarely taken from the point of view of the acceleration vector, when really the location of the peak is not as important as if they are able to maintain a higher vector than either a slower or faster index alternative.  
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Thanks again Dale very interesting - really is no such thing as a free lunch!
 
Interesting article in Guns & Ammo about the Rem model 7.  Author notes performance in the shorter barrel versions starting on pg 3.
 
 
Just bringing this all up because sometimes I think we focus on velocity a bit too much depending of course on the application intended for the rifle.  In many of my applications would gladly trade fps for a rifle that is handier.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 18:48
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Originally posted by Dogger Dogger wrote:

Thanks again Dale very interesting - really is no such thing as a free lunch!
 
Interesting article in Guns & Ammo about the Rem model 7.  Author notes performance in the shorter barrel versions starting on pg 3.
 
 
Just bringing this all up because sometimes I think we focus on velocity a bit too much depending of course on the application intended for the rifle.  In many of my applications would gladly trade fps for a rifle that is handier.
...................Great article there Dogger! Excellent... Thanks for the heads up.... Wink... I do find pages 3,4, and 5 very interesting! Whistling..........Metcalf just a little upset, that Remy increased the barrel length on the 7`s from 18.5" to 20" minimum?
 
Only a 4.5% overall velocity difference between 24" 7mm/08 and a 16.5" 7mm/08?
 
Shorter tubes inherently more accurate than longer ones?
 
I hope that some of the `ol school boys (we won`t mentioned a name; (DAWES); WHOOPS, don`t read that article while having any constipation issues...It`ll get worse................Laugh..Roll%20on%20Floor%20Laughing...............Read`n flush!..........Laugh 
 
 
 
 
 
Another hinge or nail I`d say in  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/15/2008 at 20:02
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BS in case you missed it in ballistics 101 a 7-08 is not a 300 WSM.
The more powder you burn, the greater effects of shortening a barrel.
A 22rf reachs max velocity in 16", a 300 WSM is probably still gaining at
30". You are so unappreciative of those who know so much more than you and are only trying
to educate you in the realities of basic ballistics.
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Originally posted by Big Squeeze Big Squeeze wrote:

Originally posted by Dogger Dogger wrote:

Thanks again Dale very interesting - really is no such thing as a free lunch!
 

Interesting article in Guns & Ammo about the Rem model 7.  Author notes performance in the shorter barrel versions starting on pg 3.

 


 

Just bringing this all up because sometimes I think we focus on velocity a bit too much depending of course on the application intended for the rifle.  In many of my applications would gladly trade fps for a rifle that is handier.
...................Great article there Dogger! Excellent... Thanks for the heads up.... Wink... I do find pages 3,4, and 5 very interesting! Whistling..........Metcalf just a little upset, that Remy increased the barrel length on the 7`s from 18.5" to 20" minimum?
 

Only a 4.5% overall velocity difference between 24" 7mm/08 and a 16.5" 7mm/08?

 

Shorter tubes inherently more accurate than longer ones?

 

I hope that some of the `ol school boys (we won`t mentioned a name; (DAWES); WHOOPS, don`t read that article while having any constipation issues...It`ll get worse................Laugh..Roll%20on%20Floor%20Laughing...............Read`n flush!..........Laugh 

 

 

 

 

 

Another hinge or nail I`d say in  


But, what it all works out to, after doing all the math, is the "old standard" of ~40fps/inch. Very good articles, though.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 00:39
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Cool,
Thanks Dale, even with the interruptions this was a good tread.  Now we both know why Dogger!!!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 00:55
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Originally posted by newyorkjimbo newyorkjimbo wrote:

BS in case you missed it in ballistics 101 a 7-08 is not a 300 WSM.
The more powder you burn, the greater effects of shortening a barrel.
A 22rf reachs max velocity in 16", a 300 WSM is probably still gaining at
30". You are so unappreciative of those who know so much more than you and are only trying
to educate you in the realities of basic ballistics.
...................New York Jumbo!............ I see that you are relatively new here to this particular forum with only a few posts. Welcome to the forum sir!................
 
I have several questions for you. And in the remainder of my reply to you, I will try to be as polite as possible!
 
First............Do you currently own a compact, 16.5" barreled 300 WSM?
 
Second.......If so, have you ever chronographed one?
 
Third...........Do you also own, or have access to, two 24" barreled 300 WSM`s?
 
Fourth........If yes to the first three questions, have you then, ever chronographed the        16.5" 300 WSM and then chrono`d, during the same range sessions, two 24" 300 WSM`s for velocity comparisons? Using the same identical reloading components in brass, bullets, powder, charges, primers, OAL`s, etc. etc. etc???
 
Fifth...........If yes to all of the above questions, do you also own or have access to a back up chrony, in order to compare, for comparison purposes, the findings of the first and primary chrony?
 
Sixth..........Can you answer "yes" to all of the above questions sir? Hmmm?
 
Well sir!.. I CAN answer "YES" to ALL of the above questions! So LET ME please educate or enlighten YOU sir, on "BALLISTICS 101" by welcoming you to the new powder/shorter barreled technology of the 21st century!.. Now! You may not want to read this, as it appears that you just may come from the "old school" of thinking.
 
My 16.5" 300 WSM, specifically the Ruger Frontier, does come to within 4.5% of both 24" tubed 300 WSMs using the same identical reloads. As a matter of fact sir, it averages slightly less than that, for even better results. Depending on the loadings, my carefully logged findings, show from 3.5% to a 3.9% difference in the overall velocity. Also, in an earlier article by Dick Metcalf entitled "Short Answer about Scout Styled Rifles" (also on the Shooting Times website), he even says that the average loss "IN ALL" available 16.5" Frontier calibers, will be around the 4.5% figure; 7 MM/08 OR OTHERWISE!
 
Depending upon the loads, my findings show, as compared to the two 24`s, that I lose an average of 15 to 22 fps, for every inch of shorter barrel length, or anywhere from between 112 fps to 165 fps. Another Frontier along with two other 24" 300 WSMs may have different #`s, but these sir,,,,,,ARE MY #`s!!
 
Where or how, do you come up with an analogy that I am, as you say; "so unappreciative" from or by those that know so much more, of whom are trying to educate me? I didn`t read someone "specifically" trying to educate me by referring to me on this particular thread! Did you?
 
Who pulled your chain, that would justify that kind of statement to me from you? Where do you get off sir?
 
I can back up my remarks with facts. You on the other hand, in your above post to me has done or said what?
 
Sir! Until you have the "SAME" above actual personal experience as me, regarding 300 WSM short vs longer barrel performances, then you sir, are not a credible authority. Your above opinions are fine, but they are nothing more than your opinions ONLY. Backed up with facts sir?  Actual experiences?
 
My findings fall right in line with Metcalf`s. You may not wish to agree, or have a different opinion and that is ok, fine and dandy. But don`t insult me sir, by telling me that I need,, as you say,, "ballisitics 101",, and that I am "unappreciative" of any education at the same time!.....OK!....................Have a great rest of the week and happy shooting! Wink
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 01:04
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Ok Dale, I`ll change my avatar back to those "lucious" lips now! 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 07:06
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I have always used 30-40 fps reduction per inch of barrel as a rule of thumb.  Obviously varies calibre to calibre but not a bad rule.
 
I also have long barreled rifles just in case I am giving the impression I only like the short boomers.  The rifles I shoot are application driven so varminters have longer tubes with scopes but my carry deer rifles are all short barreled, most with aperature sights. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 08:10
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Thanks Squeeze,
those eyeballs were creeping me out too, NewyorkKimbo is RMS,aka *arry aka  lonely old doorknob that has nothing better to do than piss in his own coffee each morning.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 08:37
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Dale, if I understood correctly it is generally easier to minimise the absolute velocity differences of long Vs short barrels using propellants with different burn rates in larger diameter rifles  because there is a larger bore volume and bullet surface area for the gases to work on?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 09:58
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Originally posted by Steelbenz Steelbenz wrote:

Thanks Squeeze,
those eyeballs were creeping me out too, NewyorkKimbo is RMS,aka *arry aka  lonely old doorknob that has nothing better to do than piss in his own coffee each morning.
..............Laugh.............I wanted Larry; aka NYJumbo, Niceguy, RMS or whomever to know, that if I were to ever get a hold of him in person, his eye balls would certainly do the same. He wouldn`t have the gutts to say to me, to my face, what he stated to Ed....... Ya know! His eyeballs would bulge out due to the Squeeeeeeze affect!!
 
This clown ClownClownClownClown will get on here and more than likely, try to follow me around like a little chee- waa -waa just barking at my heels, contradicting everything I post and as usual, bring nothing useful, with absolutely no proof or back up to the very things he challenges me on!..........Clown.HI LARRY!.Clown.........HowdyHowdyHowdyHowdyHowdyHowdyHowdy............Mean%20Computer 
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Squeezer, I believe below is additional support to your argument.  Me, I'm looking for a hacksaw.
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2008 at 15:18
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Interesting stuff. 
 
Indicates that a well thought out and properly executed short barreled rig need not take a back seat.
 
It then becomes more a matter of personal preference and aesthetics.
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one thing to remember though is that when you start to get into bigger diameter bullets the speed gain or loss in longer/shorter barrels doesnt change as drastically as it does in say a 6mm, my question is why is that?
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