24" vs. 20" barrel for target shooting

[Tirod]

Barrel length has less affect than bullet profile and weight. A 240 grain round nose flat base from a 24" isn't going to shoot out to the same distance as a 168 gr OTM from an 18". It will drop out of point blank range quicker and likely go subsonic sooner, too.

That's why it's known that barrel length has little to do with precision or reach, because the bullet and load behind it can affect the results significantly. Another factor is rifling - which can affect things as much as 10%, too. CHF nitrided polygonal bores have demonstrated that vs chromed button rifled.

The one thing a longer barrel can do in give an incremental increase in accuracy if iron sights are mounted on it. Lengthening the sight radius is done all the time - even extending the front sight out on a rod ahead of the muzzle. While we can empirically state the longer barrel will put bullets 10 yards further out, the better bullet and rifling in a shorter barrel can easily outmatch that.

The bigger problem is actually testing and proving it all. We can assume that certain factors are being put into play but on the firing line find that a combination of factors actually work against that one parameter. Plenty of shooters have found that the leade in the chamber was off and it defeated all the others in getting the results they expected.

And there is also the obvious choice of which cartridge - which leaves the answer about barrel length even more in peril as a significant contributor. Shoot a "bigger" cartridge and it can extend range significantly. Unfortunately barrel length rates a lot less than we'd like it to. Then it would be easy - the longer barrel would win every time. In real life, no, that isn't happening very much at all.

 

[Bart B.]

The one thing a longer barrel can do in give an incremental increase in accuracy if iron sights are mounted on it.

I disagree.

The reason front sights are extended is to make the target appear sharper in focus as the aiming eye focuses on that front sight. Good thing to do for older eyes.

The wobble area on target the aiming point moves around in some subtended angle and it doesn't change with sight radius. Good marksmen hold about 1/2 to 2/3 MOA on target slung up in prone.

 

[cdb1]

Shorter barrels do increase muzzle blast. I dont care for it.

I pick barrel length dependent on cartridge. If I can come up with a semi-logical sounding reason for it I'll come back and edit this post. It's just what feels right.

30-30, 20"
7mm-08, 7x57and .308, 22"
.270, 6.5x55 and 30-06, 24"
Any magnum(not WSM), 26"
I hunt, don't target shoot except to sight in and keep sharp for hunting.

 

[ponchh]

Velocity vs length test in Guns & Ammo ar15
2/1/16. He starts with a 26 in. barrel then cuts it off 1in. after each set of loads all the way down to 7 in. long. Many times velocity was gained with 24 over 26. Theory being after full powder burn if bullet is still in barrel that is drag.
He is shooting factory loads. Reloads can cure that with burn rates but it is a good read.

 

[Art Eatman]

I've read that in long-range target shooting, instability of the bullet's path can occur when the velocity drops below the speed of sound. In that case, a longer barrel can be an advantage.

At lesser distances, many other factors besides barrel length come into play. One effort at ascertaining the "best" barrel length for accuracy--tight groups--was done in the "Houston Warehouse": http://www.angelfire.com/ma3/max357/houston.html

 

[Jackal]

Length=velocity (to a certain point, usually around 24-26" for rifle calibers). Quality=accuracy. My LaRue lightweight barrel outshoots most peoples cheap bull barrels. Quality makes accuracy, not just weight. Now 2 barrels of equal quality? The heavier one would likely shoot best.

 

[Jim Watson]

I did a bit of F Class shooting. The Open division has such elaborate equipment as to be called "belly benchrest" and even F-T/R with lower weight limit, caliber limit, and shot off bipod instead of rest was pretty fancy and very accurate.
Strange thing, I do not recall seeing a "short, stiff barrel." I got by with 28" because on gun 1 that was what was in stock and on gun 2 that was the longest standard length without paying extra per added inch. The most common length looked like 30".

 

[coloradokevin]

This isn't an easy question to answer. You're going to have more muzzle velocity with a longer barrel, but what that means to you depends on your bullet, your atmospherics, your application, etc. If you're really trying to figure out some long range performance parameters for your build, I'd run some hypothetical numbers in a ballistic calculator to see what you get... keep an eye on the supersonic range (or even more conservatively, the transonic range; around Mach 1.2) of the bullet at various muzzle velocities, and figure out if that will get you where you need to go. Bullet flight path is often fairly predictable until you reach transonic speeds, at which point it may not be as easy to predict.

For whatever it's worth, I shoot a 20" barrel on my .308 Win. It starts going transonic (Mach 1.2) right around 1,000 yards on what I consider to be a "standard atmospheric" day for my shooting here at my 5,500 foot elevation (our air is a bit thinner, so bullets perform a bit better). That gun shoots fine to 1K... some folks consider 1,000 yards to be an incredible distance, and others would be disappointed with only shooting to 1,000 yards (again, that's an issue of individual application).

Conversely, my .260 Remington with a 24" barrel has a higher muzzle velocity, and is also firing a more efficient bullet. Thus, it goes a much longer distance before going transonic. Using an 8,000 foot DENSITY altitude figure (think: warm day at 5,500 feet elevation) that load would go transonic around 1,470 yards. But, that same bullet fired at at sea level on a 59 degree day would only get you to around 1,020 yards before going transonic.

Before your head starts to spin on all of this, please realize that I'm only trying to illustrate the fact that your individual needs will dictate your barrel length more than anything else. What are you trying to do with the gun you're building?

 

[peacebutready]

My LaRue lightweight barrel outshoots most peoples cheap bull barrels.

Even after a string of rounds fired? Ex: 10 or 15 rounds fired by both a LaRue and a cheap bull barreled rifle. The LaRue barreled rifle's point of impact won't wander as much and the groups won't expand as much as the cheap bull barreled rifle?

 

[Jackal]

Even after a string of rounds fired? Ex: 10 or 15 rounds fired by both a LaRue and a cheap bull barreled rifle. The LaRue barreled rifle's point of impact won't wander as much and the groups won't expand as much as the cheap bull barreled rifle?

Correct. LaRue doesnt use a true pencil profile, its quite a bit beefier at the chamber end. I can get it piping hot with my silencer hanging off the end and still usually overlap holes in the target using cheap American Eagle 50gr varmint tips. Whacking steel at 500y is pretty easy with the 4x scope.

 

[jmr40]

If you chronograph enough shots from different barrels you'll see more difference between 2 barrels of the same length than 2" of barrel makes. If you take a 24" barrel with a known velocity and start cutting it down to 18-20" you'll see velocity drop by 10-20 fps per inch. You'll see 50-100 fps difference between different barrels of the same length. It is entirely possible to see barrel "A" with a 20" barrel shoot slightly faster than barrel "B" with a 24" barrel. On the other hand it is also possible to see barrel "C" with a 24" barrel shoot 150 fps faster than barrel "D" with a 20" barrel. This is due to the differences in barrels, not the differences in length,

I own 3 rifles in 308. The 22" Winchester is consistently the fastest with the same loads. The 22" Kimber runs 25-30 fps slower with the same loads. The 18" Ruger varies between about 60-75 fps slower than the Winchester depending on the load. The heavier the bullet, the more difference barrel length makes in my experience.

What does that mean down range? With 178 gr Hornady ELD-X bullets the Winchester is still at 1031 fps at 1400 yards, The Ruger is getting 1012 fps at 1400 yards.