Barrel/Velocity Question


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blackops
December 31, 2009, 07:15 PM
I've always been under the impression a longer barrel does give you a little more velocity, but lately I've come across a few people that have disagreed. I would think if two people have identical rifles and identical cartridges, but one has a 20" the other a 26" the guy with the 26" is going to have an extra 200fps or so. Am I wrong here?

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matrem
December 31, 2009, 07:22 PM
Powder burn rate is a major factor in that.

R.W.Dale
December 31, 2009, 07:22 PM
I've always been under the impression a longer barrel does give you a little more velocity, but lately I've come across a few people that have disagreed. I would think if two people have identical rifles and identical cartridges, but one has a 20" the other a 26" the guy with the 26" is going to have an extra 200fps or so. Am I wrong here?

No


Sure from time to time you might have one 22" bbl that may be "faster" than one of your other guns with a 24" But don't let this fool you this is due to the differences between two different barrels aside from length.

IE if you take a long barrel and cut it down you'll ALWAYS see a velocity loss with whatever load you test

http://www.accuratereloading.com/223sb.html

Powder burn rate is a major factor in that.

NO IT IS NOT! how many times does this myth have to be busted?

matrem
December 31, 2009, 07:24 PM
NO IT IS NOT! how many times dose this myth have to be busted
Not a myth.

R.W.Dale
December 31, 2009, 07:29 PM
Not a myth.
YES YES it is!


Compare any data you wish that shows loads for rifles and hand cannons and you'll find that 9 times in 10 the top performing powders for a 24" rifle are still the top performers in a 15" encore




take hodgdon's data for 308win shooting 150grn bullets

In a 24" rifle varget is the top performer @ 2937fps
in a 15" handgun varget is still the top performer @ 2675fps

NOW note that a fast for 150g bullet powder like H-322 doesn't perform too hot in a rifle
the top H-332 rifle load is 2702 fps

so by conventional wisdom this fast powder will do better in a handgun...........NOPE

from a 15" hand cannon h-332 only gets you 2471fps compared to over 2600 with varget

matrem
December 31, 2009, 07:36 PM
Well..
My chronographs have "said" otherwise.
Usually with regard to .357 & .44 mag in leverguns.
And they use far faster powder than "expected' for that bbl length.

R.W.Dale
December 31, 2009, 07:42 PM
Well..
My chronographs have "said" otherwise.
Usually with regard to .357 & .44 mag in leverguns.
And they use far faster powder than "expected' for that bbl length.


aren't you using what's considered "slow" handgun powders to get top performence in any barrel length?

if you load .44 mag with ww231 do you expect more velocity from a handgun than a big old stiff charge of ww296. no of course you don't

You match the burn rate to the CARTRIDGE pressure rating,case capacity and expansion ratio. Barrel length is quite literally well after the fact

taliv
December 31, 2009, 07:48 PM
...to a point, of course. i mean, theoretically, if you were shooting a 223 from a 60 foot long barrel, the projectile would be gaining speed for a while, then start losing and i doubt it would make the end of the barrel.

blackops
December 31, 2009, 08:19 PM
...to a point, of course. i mean, theoretically, if you were shooting a 223 from a 60 foot long barrel, the projectile would be gaining speed for a while, then start losing and i doubt it would make the end of the barrel.

So what length barrel would a .223, 243,270, 308etc lose velocity? Normal rifles are in the 20"-26" range yet I've seen some 30". So when is length just too much? Obiously you want a length managable to carry and especially hunting, but I'm interested to what the breaking point is for length.

+ I thought slower burning powders give you more velocity as well. Still, will an extra 4" on your barrel give you that extra velocity?

Clipper
December 31, 2009, 08:40 PM
I don't have more than 22" on any rifle I own, and that's a Mosin-Nagant 91/30 I cut down. My .257 Roberts AI is 21". I recently cut my Winchester M-12 to 20" for slug hunting. The Hi-Point carbines have 16" barrels, and the velocity difference is negligible for 9mm vs a 5" pistol barrel. I still can't talk my wife into shortening her Savage 99 (.300sav) or her Rem 141 (.35rem) from 24" to a more handy 20", but I'll keep working at it...

AR-15 Rep
December 31, 2009, 08:51 PM
i'm kind of curious about those calculations as well.

bpl
December 31, 2009, 08:56 PM
I believe I've read that the .22lr begins to loose velocity somewhere in the 16"-18" barrel length range.

R.W.Dale
December 31, 2009, 09:00 PM
i'm kind of curious about those calculations as well.
Here's what 6mmbr has to say on the matter
http://www.6mmbr.com/308Win.html

.You'll see a wide range of barrel lengths and twist rates on precision .308 Win rifles. At one end of the spectrum, a tactical shooter who needs a compact, quick-handling rifle, may select a 20" barrel. The popular Rem 700 LTR (Light Tactical Rifle) features a 20" fluted barrel. On the other hand, Palma shooters, who need to keep a 155-grain bullet supersonic at 1000 yards, normally opt for barrels 30-32" in length A shorter barrel definitely delivers less velocity, all other factors being equal. With most powder/bullet combinations, you can figure an additional 25-30 fps per inch going from 20 to 25 inches. From 25 to 30 inches, add an extra 17-20 fps. From 30-33 inches you may pick up 15-17 fps or so, with appropriate powders. Here are some velocity estimates projected by QuickLOAD for 44.5gr Varget (ADI 2208) and IMR 4064 with a 168gr SMK set at 2.800" cartridge OAL, bullet not touching the lands.

notice our old friend varget is listed again even for 30"+ barrels

http://accurateshooter.net/pix/palma32inx600.jpg

AR-15 Rep
December 31, 2009, 10:23 PM
Thanks...

Uncle Mike
December 31, 2009, 10:40 PM
Still, will an extra 4" on your barrel give you that extra velocity?

It has to do with the 'peak pressure' being reached while the bullet is still in the barrel.

If your still burning powder and the pressure has not reached its maximum, and the bullet leaves the barrel, then no more pressure to act on the bullet.

If the bullet stays in the barrel until the pressure has maxed out, the bullet has been pushed as fast as it is ever going to be.

As the 6mmBR article says, yes!

Howard Roark
December 31, 2009, 10:51 PM
I know the shorter the barrel the less velocity. I also would know those ugly rifles anywhere. They belong to John Whidden. He uses a 34" blank and backbores the muzzle 2". This way he doesn't have to turn the muzzle down to accept the sight band. Turning down the muzzle diameter opens the barrel diameter where you don't want that the most.

rangerruck
January 1, 2010, 12:08 AM
dude above is right on 22lr's; after 16 inches, you bullet starts to slow down, while inside the bbl.
it all depends on what you are fireing as for a cartridge, and what is going to be it's usage. I think I read somewhere, to max out a 308 cartridge, where it won't gain any more velocity, you need a 38 inch bbl, after that , the bullet will start to slow down in your tube.
who the hell could even use a 38 inch bbl? Could you properly even see a front site mounted on that? how fat around would your bbl have to be, to stop bbl droop, or sagging from heating up? How thick and heavy then, would your receiver have to be, to keep that bbl in proper alignment?

So really it is a trade off; even for the 1000 yd shooters, who don't frickin move when they are on the line, I've never seen a tube longer than 30 inches myself, in person.

mshootnit
January 1, 2010, 12:35 AM
Actually, all you have to do to change your velocity is to point the barrel in another direction. I believe you gentlemen are more correctly having a discussion regarding speed.
http://physics.about.com/od/glossary/g/velocity.htm

Caliper_RWVA
January 1, 2010, 12:45 AM
We used barrels over 40" in the Revolutionary War... http://en.wikipedia.org/wiki/Brown_Bess A heavy profile octagonal barrel probably keeps it more rigid, but you've gotta be a heck of a man to fire that thing offhand without a bipod or something!

I expect that the problems with barrel strength and harmonics keep benchrest shooters from going too long however.

Clipper
January 1, 2010, 01:37 AM
We used barrels over 40" in the Revolutionary War...

We also used black powder...Completely different animal.

nicholst55
January 1, 2010, 01:49 AM
http://www.ballisticsbytheinch.com/index.html

CountGlockula
January 1, 2010, 02:32 AM
I need to pull out my 16 and compare with a 20 inch AR15.

elmerfudd
January 1, 2010, 02:45 AM
With just about any bottlenecked cartridge you will always lose velocity by making the barrel shorter.

With some very low powered cartridges, (like .22 CB's or Aguila caps), however you very well might see decrease in velocity with a longer barrel.

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