Understanding barrel length in relation to accuracy

[Steve Blair]

Question,

When the barrel lengths are being quoted, ie: 21-3/4" etc,

is this from the bolt face to muzzle end,

or the useable length of the barrel rifling etc ??

Tia,
Don

[br]
Bolt face to muzzle. The usable portion is called "bullet travel."

 

[BoydAllen]

When you cut off a barrel by a significant amount, in effect, it becomes a different barrel, because its vibration pattern is changed, so holding the load constant as you change a barrel's length may not be telling you as much as you think. There is also the matter of how the original load was worked up. I have seen some very good groups shot with long barrels. One of the reasons that short range (1-200 yd.) benchrest barrels are so short are the combined effects of a 10 1/2# wt. limit in two of the classes, and the desire to have a rifle balanced so that it can reliably be shot free recoil. If you want to get an idea of how well a long barrel can shoot, you need look no farther than 600yd. benchrest records.

 

[Ing. Michael W. Mayerl]

For every caliber and every load (slower faster powder) there is a different perfect barrel length.
Most barrels are too long. There is one point where the bullet gets a high velocity and low muzzle velocity spread. Is the barrel longer, the muzzle velocity rise a little bit but also the spread rise because the friction between the barrel and the bullet has a higher effect on the bullet.

For excample:

In 308 Win I prever 18-20" barrels.
In 17 HMR a 17" barrel is best.
And in the 300 RemUltraMag a 22" barrel with Norma MPR powder bring the best result with no lost of speed.

[br]
There is no such thing as a "perfect" barrel length. There may be a length that meets specific criteria best but will not work well for other criteria. Your stipulation of 18-20" for .308 may be fine for you. But, a Palma shooter needs a very long barrel, typically 30-32", to reach acceptable velocity and provide a long sight radius. [br]
As an engineer, you should know better than to make flat, unqualified statements.

You are right. A very long barrel bring more velocity but how much more ?
There is a point where you rise the barrel lenght dramatically for only some % more speed. The gun gets long and heavy.
Much more important is a bullet with a high BC.

Here an interessting article.

During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each invrement. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps).

http://www.tacticaloperations.com/SWATbarrel/

 

[Ing. Michael W. Mayerl]

+1
I also have a hard time believing that a 300-RemUltraMag is going to get all the powder burned efficiently in 22-inches. And believe in many scenarios you would see a lot of flame out the barrel.

Buy a cheap Rem700 SPS / 300RemUltra - measure the velocity with different powders with 26" barrel - shorten the barrel to 22" - mount a muzzle break like on the pic and measure again.
Than you will see what I mean.

 

[boogershooter]

This is a great topic, and efficient barrel length is something I have tried to process for a while! My gunsmith likes to keep barrels , for the most part, around 24". I understand the load is easier to tune due to harmonics etc. But I also see many records shot at mid-range (600) and long (1000), with 28, to 32" tubes. An example is the 1000 yard F- class record last year, if I recall correctly, I believe it was a 30" or a 32". I'm not here to argue, but to learn- so don't take this the wrong way!

 

[Ing. Michael W. Mayerl]

Here is also an interessting article.

RESULTS: At 33" the barrel's average velocity was only 40 fps faster than at 28".

That are 1,5% less speed for 5" shorter barrel.


http://www.6mmbr.com/BlogJan2006.html

 

[Scott Harris]

Another factor to consider is noise level. Is a suppressor going to be used with that 16" magnum? Are you going to use it for hunting and possibly not have hearing protection? It will be much LOUDer with a short barrel. You will not appreciate the difference in noise between a 20" barrel and 24" barrel until you hear them without plugs....I use 24" on my hunting rifles. Oh wait, you're going to run brake on your 16" 7SAUM.....better double up!

 

[thefitter]

Another factor to consider is noise level. Is a suppressor going to be used with that 16" magnum? Are you going to use it for hunting and possibly not have hearing protection? It will be much LOUDer with a short barrel. You will not appreciate the difference in noise between a 20" barrel and 24" barrel until you hear them without plugs....I use 24" on my hunting rifles. Oh wait, you're going to run brake on your 16" 7SAUM.....better double up!

No suppressor and not for hunting. I've not decided yet on 16" or 18"... it will one of those. I imagine the BR guys I shoot with will love it! 8) "Dang gum whipper snappers and their tacticool hardware!"

 

[LCazador]

Nobody has addressed the " time of flight or TOF factor " . Which is directly affected by barrel length , barrel resonance , humidity , elevation , ballistic coeffieceint , bullet design , friction , wind velocity , powder burn rate , cartridge efficeincy , etc.
Basically the quickest way to get it out of the barrel and to the target under the least affect from all the above , is most of the time going to be the most accurate way to get it to the target 8) ! There are too many variables in our game to claim a certain barrel lenght is perfect for that application !

 

[Killshot]

You are right. A very long barrel bring more velocity but how much more ?
There is a point where you rise the barrel lenght dramatically for only some % more speed. The gun gets long and heavy.
Much more important is a bullet with a high BC.

Here an interesting article.

During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each invrement. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps).

http://www.tacticaloperations.com/SWATbarrel/

Since Mike at Tac-Ops sells most of his builds to Law Enforcement, do you really think he's going to say the short barrels they prefer are going to give less performance? :

Objectivity is important. Generally speaking, shorter is slower and faster is better.

And we doesn't care about "heavy" in F-Class, so long as it makes weight.

 

[Steve Blair]

And we doesn't care about "heavy" in F-Class, so long as it makes weight.

[br]
"Heavy" is a relative term. If you can carry it to the line and it makes weight, it's not heavy.

 

[BoydAllen]

To say that a 20" barrel completely burns the powder is not the same thing as saying that there is no velocity loss as compared to longer barrels with the same ammunition. There is.

I know of a way to settle this. Bring one of those sub quarter minute 20" barreled tactical rifles to a F-TR match. (I don't shoot that, but I have a lot of respect for the skill involved.) If there is no significant loss of performance, and they that accurate, it should be an interesting spectacle. Think of the advertising value.

 

[Steve Blair]

To say that a 20" barrel completely burns the powder is not the same thing as saying that there is no velocity loss as compared to longer barrels with the same ammunition. There is.

I know of a way to settle this. Bring one of those sub quarter minute 20" barreled tactical rifles to a F-TR match. (I don't shoot that, but I have a lot of respect for the skill involved.) If there is no significant loss of performance, and they that accurate, it should be an interesting spectacle. Think of the advertising value.

[br]
I have witnessed your proposal in action, Boyd. In a 600 yard or under match, if the conditions are moderate and the shooter is good, he or she can be reasonably competitive. At 1000 yards, not even close. Some match directors will remove you from the line if target pullers report the rounds as subsonic.

 

[Nvreloader]

Here is some interesting info, I ran QL and came up with this info,
NOT starting a whizzin contest, etc just trying to understand Why?
Was wondering about the info you posted that this case/caliber could not be efficient in a short barrel??

I am also building a short barrelled rifle action in (16/20") pistol in the standard 284 case/caliber, for LR shooting/hunting etc.

So I will be following this post very closely.

300 RUM (MAP=64977psi max) =168gr Horn A Max=Seat depth = .460”
Case Capacity =112.5grs total, Useable Case Capacity = 104.1grs
Powder = RL-25
Load Ratio= 101.4% = 64956psi = chamber psi
95% of Powder Burnt in 11.1” of bbl length
All Powder Burnt in 17.6” of bbl length
Ballistic Efficiency = 29.2%
Muzzle Pressure = 7984psi
-----------------------------------------------------------------------------
This bbl was cut every 2” until 20” is reached, then cut every 1” untill 15”,
the predicted QL results are as follows,
Len=fps=--PB%=-95%/”=-----APB/”=------BE=----MP
40”=3712=100%=95%/11.1”=APB=17.5”=29.2%=7984psi
38”=3676=100%=95%/11.1”=APB=17.5”=28.6%=8503psi
36”=3636=100%=95%/11.1”=APB=17.6”=28.0%=9087psi
34”=3694=100%=95%/11.1”=APN=17.6”=27.3%=9748psi
32”=3547=100%=95%/11.1”=APB=17.6”=26.6%=10502psi
30”=3496=100%=95%/11.1”=APB=17.6”=25.9%=11368psi
28”=3443=100%=95%/11.1”=APB=17.6”=25.0%=12374psi
26”=3378=100%=95%/11.1”=APB=17.6”=24.1%=13553psi
24”=3308=100%=95%/11.1”=APB=17.6”=23.2%=14954psi
22”=3228=100%=95%/11.1”=APB=17.6”=22.1%=16641psi
20”=3137=100%=95%/11.1”=APB=17.6”=20.8%=18707psi
19”=3086=100%=95%/11.1”=APB=17.6”=20.2%=19924psi
18”=3031=100%=95%/11.1”=APB=17.6”=19.4%=21292psi
17”=2971=99.9%=95%/11.1”=xxxxxxxxx=18.7%=22834psi
16”=2905=99.8%=95%/11.1”=xxxxxxxxx=17.9%=24552psi
15”=2832=99.5%=95%/11.1”=xxxxxxxxx=17.0%=26465psi

Retumbo powder = APB at 19.2"/BE @ 27.5%,
Norma MRP = APB at 19.5"/BE @ 27.5%


It appears that matching the powder to the bbl lenght and load used can have some postive effects, if you want to use a short bbl, accuracy remains unknown till tested.

YMMV

Tia,
Don

There is no such thing as a "perfect" barrel length. There may be a length that meets specific criteria best but will not work well for other criteria.

+1


I also have a hard time believing that a 300-RemUltraMag is going to get all the powder burned efficiently in 22-inches. And believe in many scenarios you would see a lot of flame out the barrel.

 

[Nvreloader]

Is there a reason why you have not continued on with this post ???

Tia,
Don