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Barrel Length vs Chamber Pressure


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#1 Truckeedan

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Posted 10 May 2009 - 08:06 AM

Since velocity is reduced by approximately 30 fps for each inch of barrel shorter than the usually listed 24" barrels in published load data, is chamber pressure also reduced proportionally?I have looked all over the internet and the load manuals I have trying to answer this question. It would be helpful to know if it would be safe to exceed the maximum load in the published data to gain back the velocity I loose in a rifle with an 18 1/2" barrel. Being new to the reloading game I'm not anxious to experment when it comes to exceeding listed load pressures.Dan

#2 Yodel Dog

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Posted 10 May 2009 - 11:36 AM

...I'm not anxious to experment when it comes to exceeding listed load pressures.

+1 to that. The home reloader cannot measure pressure, all we can see is the effects of pressure.Typically, the more accurate loads are below the listed "max" loads. I'd stick to published data.

#3 gbp

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Posted 10 May 2009 - 01:59 PM

Since velocity is reduced by approximately 30 fps for each inch of barrel shorter than the usually listed 24" barrels in published load data, is chamber pressure also reduced proportionally?I have looked all over the internet and the load manuals I have trying to answer this question. It would be helpful to know if it would be safe to exceed the maximum load in the published data to gain back the velocity I loose in a rifle with an 18 1/2" barrel. Being new to the reloading game I'm not anxious to experment when it comes to exceeding listed load pressures.Dan

the answere is no they are not necessarlissy connected up or down as there are many factors that come into the equasion. we can all keep increasing powder weight but that does not corrispond to efficiency of % burnt in a given length of barrel or weight of bullet. As evidensed in my data for 280 rem. that is my data not anyone elses. it works in mine and mine alone and just as any published data should be treated as such. Personally i highly recommend getting a copy of quickload and tayloring data to yourself and your weapon.

#4 Fjold

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Posted 10 May 2009 - 02:59 PM

No, the reason that the velocity is lower in a shorter barrel is because the force (pressure) is applied over a shorter period of time.

#5 Frank

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Posted 10 May 2009 - 03:33 PM

if it would be safe to exceed the maximum load in the published data to gain back the velocity I loose in a rifle with an 18 1/2" barrel.

Well, the SHORT answer would be MAYBE... or maybe NOT! Too many variables & is not a black & white issue.Often times, it very well may be safe, however, accuracy usually goes south, IF you really are at the max load & go above that (max). Often times folks really are not at their max load, especially if only going by "published data". Manuals are only guidlines & can be a country mile off. I was just looking at Hornadys yesterday & shook my head in disbelief. Made me wonder if we were even talking about the same subject.I guess the bottom line to what you are trying to do is; DON'T! If you want more velocity use a longer barrel and is why 90% of my rifle barrels are 26". Your 30 fps guidline per inch is indeed pretty right on, but I have seen as much as 60+ fps per inch in velocity loss in certain calibers. 204 & 223 not much loss; 22-250 or 257 mag can be HUGE losses! One point... I will have to respectfully disagree with yodel Dog on more accurate loads being below max. Nothing could be further from the truth. Unless you are WAY below max. On occasion, yes, middle loads can be the most accurate, but not normally. The most accurate loads are usually the max or lightest loads. And again, if only going by "book" max one is only guessing & can be a mile off. One MAJOR powder company does not even test for accuracy with any of their listed loads. They have told me that more than once by the phone. Good LuckFrank

#6 Panoche_Walker

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Posted 10 May 2009 - 09:50 PM

No, the reason that the velocity is lower in a shorter barrel is because the force (pressure) is applied over a shorter period of time.

+1Also have to agree with Frank(2nd Frank) on the "Don't" advice.

#7 clampdaddy

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Posted 11 May 2009 - 06:20 AM

....One point... I will have to respectfully disagree with yodel Dog on more accurate loads being below max. Nothing could be further from the truth......

It's a crapshoot. Some powders will produce better accuracy with lower charge weights and others do better juiced up a bit. In my 25-06 and a 75gr v-max I get the same accuracy with a light charge of H-414 as I do with a max charge of H-4350. Same goes for my pet 30-06. A light charge of IMR-4320 shoots really well with 150gr bullets but so does a max charge of IMR-4350.

#8 A17Shooter

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Posted 11 May 2009 - 07:31 AM

Have you guys forgotten the article in a 1994 issue of Handloader concerning LeDuc's equation? Well Dan Lilja has a posting on his website concerning it and the way it predicts the effect of different barrel lengths on muzzle velocity. Dan is writing about a 50 caliber but, the principles apply to all calibers.DON'T DO AN OVERLOAD TO TRY TO MAKE A SHORT BARRELED GUN SHOOT THE SAME VELOCITY AS A LONGER BARRELED GUN WITH THE SAME CARTRIDGE! You'll just make a bomb.Link to Lilja's article

#9 predcaller

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Posted 11 May 2009 - 09:19 AM

is chamber pressure also reduced proportionally?No Chamber pressure is highest when the powder is ignited, then a second peak as the bullet enters the rifling. The pressure then starts to steadily decrease as the bullet travels down the barrel. The pressure is being generated until the powder charge has fully burned up and the gasses generated by the powder burning have stopped. The burn rate of a powder governs how long these gasses will be generated. So the answer is the barrel length has no effect on the peak chamber pressure and adding powder to try to compensate for a shorter barrel is just dangerous. A powder with a faster burn rate will make up some of the difference for a shorter barrel.

#10 Truckeedan

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Posted 13 May 2009 - 09:08 AM

Thanks Predcaller and A17. Both good answers that make a lot of sense. Can't look a gift horse in the mouth. The gun was free and shoots under an inch after bedding so I will be happy with a few less fps and not risk a bolt in the face.Dan




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