Calculating Optimal Barrel Length

[briannmilewis]

We are working on our 223 Short wildcat, and it occurred to me that we should at least know the optimal barrel length for a rifle, and I do not know if this will vary based on twist rate.


Is there any other way (apart from physically cutting down a barrel and measuring performance at each length) to calculate optimal barrel length for a cartridge other than the ball park 100fps - 150fps loss per inch of barrel, from a known starting length and fps?


Currently, Shane has the following setup and basic performance:


223 Short, 1 - 7 twist barrel @ 23.5" long, CCI BR-4 primers, Lake City 223/Rem 221 FB/Win. 223 brass, Hodgdon Lil'Gun powder

40gr Hornady V-Max over 12.7gr. = 3184fps

55gr. Hornady V-Max over 12.3gr = 2730fps

The 35g - 46g bullet tests will be in a Savage 23.25" barrel.

[Reverend Recoil]

I have not done such a thing but this is how I would approach your problem. 

To calculate optimal barrel length for a cartridge you will need access to a well equipped ballistics laboratory.  The pressure vs. barrel length curved is derived from the data collected from a pressure test gun, stress gages, high speed timer, and recorder.  This data is plotted in the form of a graphic curve.  A mathematical formula is derived that closely fits the curve.  The acceleration of a bullet down a gun barrel is a related rate so you must then integrate with respect to barrel length to get the acceleration formula.  With the acceleration formula one could determine the optimal barrel length.  If optimal is when the bullet is on the verge of coasting out of the barrel then you will likely need a barrel five to eight feet long.  Maybe longer.
 
Is this more trouble than it may be worth?  Maybe so.  It all depends on how close to ‘optimal’ is good enough for you.
 
For most sporting rifles the handling qualities of the gun are more important than the difference in performance of a long and short barrel.

[wncchester]

I'm 71, been an avid shooter since my teens and a reloader since the early 60s but must confess I have no idea what would define the 'optimum' rifle barrel length.   What criteria or values would you be using to define that?

[tacklebury]

I'd think that you probably want to get a program like QuickDesigner and Quickload to test these types of parameters.  I've had my buddy develop a load and use my barrel length of 35" (for my 7.5x55 swiss) to make sure we get 100% burn of the speed of powder I'm using.  I don't honestly believe you will ever obtain one single optimum, because much of it is variable due to powder, bullet (thus resistence and frictional) and even bullet shape. 

[cwlongshot]

Optimal for what...
 Since it would have to be based on a given bullet weight, moved by a given powder and powder charge from that powder, sparked with a certain primer, all loaded in a certain case. Fired from a barrel with XinX rifling and all that at a certain elevation and only at certain climatic conditions. I surmise that just like my weight is PERFECT for a 7' tall man, your barrel length is also just perfect as it is...  Its like roping the wind...
 
I tend to to worry too much for things that are beyond my control. (My cardiologist would be proud) There are a hundred different saying s that apply.. Dance with the one that brung you... Play the hand that's delt ya... I think you get the picture.
 
My advice, VERY roughly stated 22" for std calibers and 24" for magnums, 2-6" for pistol calibers. This has worked with what we have for calibers for up to the past hundred years... don't try to fix whats not broke. Find a bullet, powder you and your barrel likes and stop worrying about such things.
 
CW

[briannmilewis]

All fine advice. The little blurb that Reggie sent me to read on the 6mmBR website pretty much said that extra length doesn't buy much in fps, shorter the stiffer the barrel helps with a scoped rifle, longer barrel with iron sights helps.


As far as street specs for a H&R: 22" heavy barrel and 18" light barrel would be good starting points, there isn't much powder to burn.


Thanks to all.

[JMcDonald]

In a nutshell, most rifle calibers won't see peak velocities until at least 35" of barrel. The tiniest ones like .17 Bee or .22 Hornet might peak earlier (maybe 30"), but at the same time many will peak later (like 46"+ heh).
http://www.gboreloaded.com/forums/index.php/topic,243543.0.html
 
I'd bet money that the only standard cartridges which will see peak velocities before even 30" of barrel length are pistol and shotgun loads. Even moderate loadings like .223 will still be accelerating in a 26" barrel.
 
That said, I think it sounds kindof exciting to get a super-heavy barreled rifle in like 35" made for a big cartridge like .30-378 .

[calvon]

cwlongshot said: "Optimal for what... 
 Since it would have to be based on a given bullet weight, moved by a given powder and powder charge from that powder, sparked with a certain primer, all loaded in a certain case. Fired from a barrel with XinX rifling and all that at a certain elevation and only at certain climatic conditions. I surmise that just like my weight is PERFECT for a 7' tall man, your barrel length is also just perfect as it is...    Its like roping the wind...


benchrest shooters like long heavy barrels. Small game hunters like short handy light weight rifles. Woods hunters like short handy rifles. What may be optimal for one might be the exact opposite for another. Tailor your barrel length to the job at hand.
"

[JMcDonald]

And I think he means "academically" optimal as far as peak velocity goes.
 
And even for a rifle cartridge using LilGun, I'd be surprised if the bullet reached peak velocity in anything under 30". Now, we'd probably be talking about 50fps from 25 to 30", but it would still be there. However, as stated, a 16" barrel might be completely practical for some uses.
For example, my .308 Handi has a 16.4" barrel. While it is far from optimal for getting the most out of the caliber, I now have a 27.5" gun with an easy practical range of 250+ yards, that is still capable of taking just about anything in the lower 48 (or anything else I'd want to do with it).

[flashhole]

Don't know that I can add to this conversation but I certainly want to follow it.
I read and read the OP and concluded he was talking about velocity when he meant "optimum".  Interesting that my perspective for optimum involves accuracy and repeatabiligy, not so much velocity.  The comments "optimum relative to what" pertaining to the load and bullet selection are spot on.  Rigid barrels have less flex ... translates to better repeatability ... translates to better accuracy.  IMO too many variables in other parts of the gun to make definitive statements about the barrel being the principle contributor to optimization.  Would like to see the 35" barrel though..

[RaySendero]

Yeah, I'm kinda with flashhole on this one!
 
I've not seen any bottleneck rifle cartridge that slowed down in velocity even out of 30" barrels like a 22LR will do in about a 18" barrel!
 
But am will to be convinced.

[JMcDonald]

I actually spent like an hour today looking into stubbing a Handi into something like a .300 Wby / RUM or even a .30-378 with a 35"-long, 1.25"-diameter barrel . That would make for like a 350yd PBR varmint rifle that is still capable of taking anything under 1000lbs . Plus it would look way sweet, heh.
 

[fastchicken]

the ball park 100fps - 150fps loss per inch of barrel, from a known starting length and fps?

I've always thought it was more like 25-50 fps per inch, which has been about right from my experience

[LanceR]

Remington, Lyman and others have published data on this subject.  A good article is at:

http://www.chuckhawks.com/rifle_barrel.htm

Lance

[Catfish]

The burn rate of the powder used would be a big factor. I know a gun smith that did so experments with barrel lenth. I`m not sure what caliber he was useing, but he started with a very long barrel and sawed off 1 in. at a time and then recrowned it an tried it again. He was able to get the same velocities by useing faster burning powders, and you can get barrels long enough to slow down bullets, especially with slower burning powders.

[tacklebury]

I actually spent like an hour today looking into stubbing a Handi into something like a .300 Wby / RUM or even a .30-378 with a 35"-long, 1.25"-diameter barrel . That would make for like a 350yd PBR varmint rifle that is still capable of taking anything under 1000lbs . Plus it would look way sweet, heh.

Just FYI, handi receivers aren't designed to deal with magnum caliber head thrusts and it's typically considered a no-no.  I think you might look more at a Rolling block #1 action for those higher pressure cartridges.  Just don't want to see ya get hurt. 

[JMcDonald]

Hah yeah I figured it wouldn't be realistic, but a boy can dream can't he? . And like I said above, I don't have any need that my "shorty" .308 can't fill (and even then I'm not up for doing everything it's capable of), so it was largely academic, heh.

[tacklebury]

hehe.  I've had some similar thoughts. 

[briannmilewis]

Shane gets 3000+fps plus sub-MOA accuracy out to 300 yards with enough energy to cleanly kill a coyote with the 223 Short using a 23.5" barrel, using as much or less powder as a 22 Hornet.


After everyones answers, I think and practical barrel length is not an issue to worry about.


The 223 Short is getting more interesting all the time. 221 FB performance using 2/3 of the powder.


I think this is attributable mostly to new powders like L'il Gun in small cases. Benchmark produces crazy accuracy with less velocity.


Thanks again.