The impact of barrel length on Velocity
This article will both answer a reader question regarding handgun ammunition velocity and serve as a perfect segway into the upcoming Terminal Ballistics series.
“I’ve thoroughly enjoyed the Internal and External Ballistics series. It seems, however, that most of your material applies to rifles and rifle ammunition. I’ve recently read about Remington’s Ultimate Defense ammunition designed specifically for compact handguns. You’ve mentioned barrel length in your Internal Ballistics series contributing to precision and accuracy, but haven’t spoken very much on velocity. How much does barrel length impact ammunition velocity in compact pistols?” – Mark in Murrieta
Thank you for the note, Mark. I appreciate the question and the opportunity to answer it here. As a general principle, barrel length and initial velocity are directly proportional… meaning that longer barrels tend to produce higher muzzle velocities and shorter barrels tend to produce lower muzzle velocities. This is due to the duration in which burning propellant provides the gas expansion to thrust the projectile forward. Keep in mind, though, propellants have different burn rates based on their composition and construction. Some propellants have a “flake” construction which maximizes the surface area for the volume of each flake and tend to burn much faster than “stick” type propellants (which look like broken pencil lead) which are more dense with less surface area and burn relatively slower.
You raise an interesting question worth exploring here. Ammunition manufacturers, in general, mass produce their products within tolerances (overall length, diameter, and powder charge) that will function in the widest variety of firearms… and thus will sell the most units and provide the greatest profit margin available to stay in business. If you have noticed, many of these manufacturers also print the ammunition velocity on the box for their specific brand and type of ammunition. As a corollary to your original question, it is also interesting to consider how closely the published handgun ammunition velocity matches your individual firearm… if at all. While these manufacturers publish a velocity, most do not list the type of firearm it was fired from or the atmospheric temperature in which the measurement was taken.
While I’m sure there is a series of mathematical formulas which can model different conditions, I believe I threw enough of those at you in the Ballistics series so far. Instead, I decided to conduct a test and publish the results for your consideration. On 14 Nov, I took a trip to the rifle/pistol range at the Izaak Walton League in Arlington/Fairfax and set my Shooting Chrony Alpha chronometer 12 feet in front of the firing line to test American Eagle 115gr Full Metal Jacket 9mm ammunition through four pistols with different barrel lengths.
The Shooting Chrony Alpha is a relatively inexpensive tool which measures projectile velocity. It is a simple box with two photo-electric sensors at a known distance apart. Set-up far enough away from the firing line to avoid muzzle blast (approx 12-15 feet), the projectile passing the first sensor starts an internal stopwatch which is then stopped when the projectile passes the second sensor. Since the distance is known (it is the length of the chrony case), a simple digital algorythm calculates distance divided by time and indicates the velocity in feet per second.
For this test, I selected: the Sig Sauer P938 9mm sub-compact pistol with its 3.6 inch barrel; the Glock 19 9mm compact pistol with its 4 inch barrel; the Smith and Wesson M&P Carry 9mm pistol with its 4.25 inch barrel; and the Glock 34 competition 9mm pistol with its 5.31 inch barrel. I fired 10 rounds of the same lot of American Eagle 115gr FMJ ammunition from the same lot through each pistol. American Eagle lists the muzzle velocity for this ammunition as 1,180 feet per second (f/s).
– Sig P938: Average Velocity 1,031.70 f/s; Average Energy 271.77 Joules
– Glock 19: Average Velocity 1,072.20 f/s; Average Energy 293.54 Joules
– Smith and Wesson M&P 9 Carry: Average Velocity 1,096.79 f/s; Average Energy 307.10 Joules
– Glock 35: Average Velocity 1,153.6 f/s; Average Energy 339.79 Joules.
Did American Eagle ammunition misrepresent their product by listing 1,180 f/s as the velocity for this product? No. Keep in mind, they specified neither the firearm type nor the temperature in which the ammunition was tested. My test was conducted at 44 degrees Fahrenheit, which may be considerably lower than the nominal 68 degree “room temperature” under which most other tests would be conducted. Since the average velocity from the long-barreled G34 was 1,153.5 f/s, it is entirely plausible that it would have functioned at 1,180 f/s in 68 degree weather.
For comparison, I shot some 230 grain .45ACP out of my Wilson Combat CQB on this same day in 44 degree weather and compared it to a test I conducted with the same ammunition in 82.2 degree weather in July. The same ammunition through the same pistol was 23.1 f/s slower in the colder weather, thus reinforcing the findings with the American Eagle 115gr 9mm FMJ.
So, other than the obvious, what does this test tell us? The difference between shooting this specific ammunition through a 5.31 inch barreled Glock 34 and the 3.6 inch barreled Sig P938 is a velocity difference of 121.9 f/s, or roughly 11%. I listed the average energy for the projectile traveling out of each firearm to also illustrate the difference in energy, which is nearly 20% between the shortest and longest barrels.
This is an important consideration when choosing personal defense ammunition. What is printed on the box is a performance guideline that may not function exactly as advertized in your particular personal defense firearm. A type of personal defense ammunition that advertises 1,200 f/s velocity and projectile expansion may not reach that level of velocity or terminal performance when shot out of your subcompact pistol. You also need to consider the environmental conditions under which you may need to employ your firearm and ammunition. It is not only shorter barrels that produce lower muzzle velocities, colder temperatures also contribute to slower muzzle velocities.
As with any other product, it is up to the buyer to do the research and go beyond the advertising and hype. It is up to you to do the research to determine which personal defense ammunition is best for your applications that is also matched to your firearm. Consider both barrel length and average inside and outside temperatures. Above all, choose one that functions flawlessly without stoppages.
Mark, back to part of your initial question, you mentioned Remington’s Ultimate Defense Compact Handgun ammunition. I looked it up and it states: “For maximum terminal performance in handguns with barrels of 4″ or less. With a brass jacket hollow point optimized for the lower velocities generated by shorter barrels, this load delivers the massive expansion and deep penetration you need in the face of danger. After dark, our proprietary low-flash propellent protects night vision for more accurate follow-ups.”
This all sounds entirely plausible and this is the first ammunition that I’ve seen manufactured for shorter barreled pistols, other than the ubiquitous .45 GAP (Glock Automatic Pistol). At this time, I do not have enough data to tell you if it lives up to its claims or not. For this, I return to my previous point, you’ll need to test it in your specific firearm.
Thanks to Mark for sending-in the question and thanks to all of you for taking the time to read this article. Please check-in again soon for my Terminal Ballistic series where I cover projectile impacts on target.
If you have any comments or experiences with defensive pistol ammunition that you would like to share of if you have any questions that you would like the Aegis Academy staff to answer, sound-off in the comments below or shoot me an e-mail at firstname.lastname@example.org.
Until then… stay safe and shoot straight!