Longer barrel = higher velocity?

[Telecaster]

I recently read some test results where a 4" 686 spat out bullets at a lower velocity than a 3" revolver in some types of ammo. That got me wondering, and a google search says barrel length does not automatically correlate to velocity when comparing different guns. Ok, fair enough.

So, I lugged the chrono out to the range to see what I had.

S&W 640, nom. 2" barrel
Taurus 856, 3"
S&W 65-5, 3"
Ruger GP100, 3"
S&W 686-5, 4"

I tried five different kinds of ammo. One .38 Special 158 gr LRN, four .38+P defensive loads, and one .357 defensive load (Hornady Critical Defense). I only shot the .357 in the 65, GP, and 686.

My five samples did indeed correlate barrel length and velocity, so no surprises there. The 3" revolvers all had about the same velocities for each ammo type. "Not enough difference to make a difference," as Paul Harrel says. The .357s were similarly clocked. The 4" barrel added just 2 to 9% more velocity over the 3", which was less than I expected. The 2" barrel provided 90 to 94% of the velocity of the 3" barrel.

None of this determines whether hollow points expand or not, that's a whole different test.

Has anyone else done this comparison?

 

[OKFC05]

Everyone who shoots action pistol competition must "Pass chrono", so becomes aware that what matters is Your Load in Your Gun, today.
I have two "identical" 4" model 66's, one of which consistently shoots identical minor power loads about 30 fps faster than the other.

 

[Alk8944]

Even though your test showed longer barrels develop higher velocities than shorter barrels, Tain't necessarily so! In the older Speer loading manuals there is a table of several revolvers of different barrel lengths and makes, all in .357 Magnum, and same brand ammunition The table shows the velocities obtained by chronograph. The disparity between what would be expected and what really was is amazing.

I bought an Oehler 35P chronograph about 30 years ago and have tested thousands of rounds of everything I shoot. Sample size is always 5-10 rounds, sometimes greater, and in several barrel lengths the same day. I have several loose leaf binders of data collected over this time. Often I have found that a 4" barrel will often give higher velocity than a 5", 6" or sometimes even longer barrels, depending on what I own at the time.

For just one example, I have an old Colt Officer's Model Target .38 Special with a 7 1/2" Barrel. This is a very uncommon barrel length for this model! Most of of my other revolvers will give higher velocity with barrels of 4", 5", 6", and, surprisingly sometimes even my 2" guns. This includes both .38 Special and .357 Magnum chambered guns.

I don't know what your habits are, but any chronograph data obtained from samples of less than 10 rounds has little statistical value. 5 rounds can be close, but questionable. The larger the sample size the more meaningful the results that are obtained.

 

[LVSteve]

I've read enough articles and seen enough YT videos to be convinced that sometimes you get fast barrels, and sometimes you get slow barrels. Revolvers have an added variable, the cylinder gap, to muddy the waters.

 

[mikerjf]

And there’s the question of freebore. I’ve seen it suggested that while the revolver’s cylinder gap may lose some pressure, if the cylinder length means more freebore than an auto has, the revolver may wind up the faster of the two.

I’d love to see a test of gradually increasing freebore in a test barrel against velocity.

 

[IAM Rand]

I saw a test done where the guy started with a really long barrel and then cut it down an inch at a time I think it was. I do believe that longer barrels produce more velocity. I think the problem with what you did is use different guns. Barrels are going to act differently even from the same manufacture. The only true test is to take the same barrel and cut it down to see how it changes in length.

 

[murphydog]

Surprised no one has mentioned load variability. Some ammo meant for shorter barrels will not go any faster in a longer barrel, while others (the .22 Magnum rimfire rifle loads come to mind) appear to keep increasing velocities all the way out to 20-24" barrels. In a handgun all that extra unburnt powder and pressure makes for quite a lot of flash and noise.

 

[stansdds]

Generally speaking, a longer barrel does equate to higher velocity, but every firearm is a rule unto itself.

Variables that affect velocity would include the burning rate of the powder, the pressure generated by the powder/bullet combination, case neck tension on the bullet, the dimensions of the chamber, distance from the case mouth to the rifling, barrel bore and groove dimensions, smoothness of the internal surfaces of the barrel, and, to a small extent, the barrel-cylinder gap. All of these can add up to some general rule breaking results.

 

[steelslaver]

Velocity by the inch did the cut the barrel down 1" at a time testing and also used a variety of ammo at each length.
The only instances where shorting a barrel increased velocities were in the 15"-18" lengths


They also did some testing with a barrel set at 0 gap, .001 gap and .006 gap. The first .001 gap cause way more loss than the next .005.

BBTI - Ballistics by the Inch :: Home

 

[Rock185]

Been chronographing for 40+ years, and yes, longer barrels "usually" produce higher velocities. But for all the reasons stansdds mentions, sometimes the shorter barrel produces a higher velocity. The Speer manual article, "Why ballisticians get grey", by Dave Andrews is an excellent explanation of this fact..

 

[BC38]

I recently read some test results where a 4" 686 spat out bullets at a lower velocity than a 3" revolver in some types of ammo. That got me wondering, and a google search says barrel length does not automatically correlate to velocity when comparing different guns. Ok, fair enough.

So, I lugged the chrono out to the range to see what I had.

S&W 640, nom. 2" barrel
Taurus 856, 3"
S&W 65-5, 3"
Ruger GP100, 3"
S&W 686-5, 4"

I tried five different kinds of ammo. One .38 Special 158 gr LRN, four .38+P defensive loads, and one .357 defensive load (Hornady Critical Defense). I only shot the .357 in the 65, GP, and 686.

My five samples did indeed correlate barrel length and velocity, so no surprises there. The 3" revolvers all had about the same velocities for each ammo type. "Not enough difference to make a difference," as Paul Harrel says. The .357s were similarly clocked. The 4" barrel added just 2 to 9% more velocity over the 3", which was less than I expected. The 2" barrel provided 90 to 94% of the velocity of the 3" barrel.

None of this determines whether hollow points expand or not, that's a whole different test.

Has anyone else done this comparison?

IIRC, the tables in the Ballistics By the Inch website show that for almost all cartridges, if fired in otherwise identical guns, the velocity increases pretty linearly with barrel length up to around 18" before the velocity starts to drop slightly due to friction between the barrel and bullets.

It has been a couple of years since I last looked at that specific aspect of their ballistics testing - when I was trying to decide between buying a lever gun with either a 16" barrel or a 20" barrel.

With revolvers there is an additional variable though - the cylinder gap. Two revolvers of the same model with different barrel lengths can also have different cylinder to barrel gap measurements - which can cause some unexpected anomalies in the actual results.

 

[steelslaver]

While an increased B/C gap will cause an increase in velocity loss, it is far less than most believe. I doubt an increase of .001 causes a 5 fps loss in most cases. I would bet that everything else being equal going from .006 to .008 is well under 10fps as the majority of loss is in the first .001 of gap. Ballistics by the inch took a single action 357 and as they cut the barrel down an inch at a time, they also installed it tight against the cylinder .000 gap, then with .001 gap, the again at .006 gap and test fired it with various ammo at each stage.
If you look at the tables for the various ammo fired, in MOST instances the loss cause by increasing the gap from .001 to .006 was less than 20fps and that was almost always far less than the loss cause by going from no gap to .001

Interestingly on rare occasions there was actually a increase in velocity when the gap opened

Increasing the barrel length always increased velocity until over 15" and then in a few cases it dropped a little bit