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Barrel length vs velocity
Discussions related to Guns and Firearms
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1895ss
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PostPosted: Sun Nov 20, 2005 10:42 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Good Luck !!!!!!!! Smile

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kbis
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PostPosted: Mon Nov 21, 2005 7:05 pm    Post subject: Re: Barrel length vs velocity Reply with quote

This is really getting complicated, I just wanted to know if you were shooting brand what ever bullets out of say a 22" barrel and shot the same bullet out of say a 26" barrel about how much increase in velosity you expect to see.
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Bushmaster
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PostPosted: Mon Nov 21, 2005 7:16 pm    Post subject: Re: Barrel length vs velocity Reply with quote

50 to 100 fps, maybe more depending on the barrel condition...

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Handloader
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PostPosted: Thu Nov 24, 2005 7:01 pm    Post subject: Re: Barrel length vs velocity Reply with quote

I want to delve into Expansion Ratios with a bit more background and information to compliment a previous post. Beforehand, however, let me state up front that it is rather esoteric and probably has little bearing on what we actually do at the loading bench or in the field, yet, the principals of it govern what we are doing regardless. But it will give a better understanding of what we are trying to achieve even if my presentation of some of the information is a bit borish for which I apologize beforehand.

Years ago, 1961, Homer Powley developed the "Powley Computer for Handloaders" and the "Powle PSI Calculator". In reality, these were two sturdy slide rule affairs made of high quality cardstock that allowed the input of inter related numbers that, in turn, gave predictable results.

Powley's goal was to assist the handloader in developing loads that gave maximum efficiency with their cartridge in rifles of varying barrel lengths. He was a ballistician expert that put some seemingly complex factors into basic language. His work was revealing to me and gave me some insights as to what constituted a predictably good load from a mediocre one.

Using the Powley computer allowed the selection of the proper powder (correct load density/burn rate) for the proper bullet weight in the specified chambering and to the predictable best working pressure. This would result in the most efficient load and, usually, the best load specific to SDs, something that became verifiable when the cost of chronographs allowed anyone to own one. His work was oriented to IMR powders as that is what the majority of handloaders used at the time but the data is easily interprolated into other powders with use of a Burn Rate Chart.

I could expound on all the intricacies of component and powder selection based on Powley's writings but, thankfully, will not. Let's cut directly to the term "Expansion Ratio" as it is critical to understanding the primary issue of this thread, "velocity vs barrel length".

ER is simply the ratio of the total volume of the barrel to case capacity. Quoting Powley, " . . . it is the numer of times the gas will expand by the time the base of the bullet reaches the muzzle." The lower the ER, the lower the efficiency of the cartridge. The paradox is that lower ER rifles will give higher velocity. The critical thing here is that ER has the basic function in determining the highest velocity a given bullet has in a given bore size.

To effectively use ER, the term "Ratio of Charge to Bullet Weight" must be included and that simply is the percentage of powder by weight relative to the weight of the bullet which is summarized, in turn, by its sectional density for boresize. Today, we have real computers to do this heavy work for us. But, the results are going to be based on basic manipulation of these two aspects of control the handloader has, ER and RoCtBW". Powley simply gave us these tools early on and inexpensively.

By manipulating the barrel length in his equations the new velocity would result and it would depend on burn rate and expansion ratio. Regardless of the barrel length, the proper powder will be the same contrary to what some believe that the shorter the barrel, the faster the powder should be to compensate. Any compensation is simply be achieving higher pressure.

Other observations: a pound of powder has the same engergy regardless of the burn rate! Burn rates simply allow us to use powders that give the best volumetric filling of the cartridge while producing the ideal pressure for the most uniform velocity and consequent barrel life. This is one reason I appreciate the Nosler reloading volumes as they give the load density and velocity at SAAMI max pressure for the cartridge. Note that anytime 40,000psi is exceeded, the temperature of the load will exceed the melting point of the barrel's steel. Pressure and temperature are different expressions of the same amount of "work" done by the load.

The shortcut to good loading begins by selecting the powder that gives the highest density and the highest velocity. This basically means that the efficiency of the cartridge is best with this powder(s). The powder that does this is always the first powder that I try when developing a new load.

Powley's computer and the Nosler reloading manual have allowed me to cut my load development rounds to usually 20 to 30 rounds. Chronographs and targets confirm the results and while added rounds may be spent on fine tuning the load for bullet length or primers, most often these two factors (Powley/Nosler) give me the beginning tools.

If you ever see a Powley Computer in its little brown envelope at a gunshow, grab it. It is fun and informative.
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Bushmaster
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PostPosted: Sun Nov 27, 2005 4:56 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Man... I bet Kbis really need that disatation...Thanks Handloader... Ignore

I've been reloading for quite a while and thought I was really up on the length of a barrel and the velocities obtainded by an extra inch or two...Now even I'm confused... Confused wtf

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kbis
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PostPosted: Sun Nov 27, 2005 5:55 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Bushmaster- you are right. I did not realize that it would take an IBM main frame to figure this out. I was just wondering if I had the choise between 2 rifles ( same manufactor) in the same cal. and using the same ammo. About how much difference would there be between the two in muzzel velosity if one had say a 24 inch barrel and the other had a 26 inch barrel?
Just a general question, thats all Smile .
Thanks for the inputs.
Ken
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Handloader
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PostPosted: Sun Nov 27, 2005 11:38 pm    Post subject: Re: Barrel length vs velocity Reply with quote

kbis: not much.
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1895ss
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PostPosted: Mon Nov 28, 2005 9:13 am    Post subject: Re: Barrel length vs velocity Reply with quote

Bushmaster like you I've been reloading for a long time and I'm confused now as well wtf Confused Shocked Confused


kbis, this is a general rule of thumb according to Remington.

MV 2000-2500 fps, the approximate change in MV per 1" change in barrel length is 10 fps.
MV 2500-3000 fps, the approximate change in MV per 1" change in barrel length is 20 fps.
MV 3000-3500 fps, the approximate change in MV per 1" change in barrel length is 30 fps.
MV 3500-4000 fps, the approximate change in MV per 1" change in barrel length is 40 fps.

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kbis
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PostPosted: Mon Nov 28, 2005 3:18 pm    Post subject: Re: Barrel length vs velocity Reply with quote

I guess it doesn't make much difference, per your chart. I just happen to like the longer barrel, I am that much closer to the target and I need all the help I can get Very Happy .
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Bushmaster
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PostPosted: Mon Nov 28, 2005 3:23 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Some, but not much. My A-Bolt has a 22" barrel and sends them out there as fast as I will ever need. And you are right. You would be 4" closer then me...

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PostPosted: Mon Nov 28, 2005 4:23 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Handloader, Toilet Claw Toilet Claw Thumbs Down Sleep Bonk Idea Question Argue Ignore

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PostPosted: Mon Nov 28, 2005 4:27 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Ash...Come on people...Handloader was trying to help. Give him credit... Flag

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PostPosted: Mon Nov 28, 2005 4:39 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Certainly.......................... Poke

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Last edited by 1895ss on Mon Nov 28, 2005 9:19 pm; edited 1 time in total
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JO422
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PostPosted: Mon Nov 28, 2005 6:31 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Kibis,

The difference in velocty is about 20FPS per inch of barrel. That means about 120fps between a 20 inch and a 26 inch barrel. Last spring I was at a precision rifle course where some guys were shooting 20" barrels and others had 26" barrels. At 300 yards there was not much difference, the 20" barrel guns had to make about +1/2 MOA (1.5") more elevation adjustment than the 26" barrel guns Confused . Not a whole lot when you consider the shorter and handier characteristics of the 20" barrels. The differences obviously increased with the distance, but not enough to justify the extra 6" barrel length. By the way, I am not one of the 20" barrel shooters, mine was a 26 incher. If I was buying today I would get ther shorter barrel, have a handier rifle and learn my "dope" at extended range. Good luck in your choice.
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Bushmaster
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PostPosted: Mon Nov 28, 2005 6:56 pm    Post subject: Re: Barrel length vs velocity Reply with quote

Hummm. I never thought of that. J0422. But now that you mention it, one of my friends has a 20" barreled Remington 740 or 742 (can't remember which). It is semi-auto in .30-06 and it shoots as well as my 22" A-Bolt...Out to 300 yards...You have a point that many (including me) may have forgotten...

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