Power by the Inch
Ever wonder how much velocity and energy you give up if you select a 2-inch barrel over a 4-inch barrel? We all know that the longer the barrel, the more velocity we can get out of a cartridge. We also know that shorter barrels are the less velocity and power we get.
But have you ever wondered how much you're really giving up by selecting a 2-inch revolver or a 3-inch 9mm? What about using a 3-inch .45 instead of a 5-inch Government model? Well, now you can find out some real-world examples.
In years past, gun writers have promoted, as a rule of thumb, that you lose 50 fps per inch of barrel. As it turns out, that's not quite true, depending on the load's construction. For example, for a selection of 9mm rounds in barrels between two to six inches long, the average variation ranges from 41 to 81 fps.
This information is at your fingertips, thanks to four very inquisitive guys. Jim Kasper, Jim Downey, Steve Meyer and Keith Kimball took it upon themselves to find out and document the question of how barrel length affects velocity. And they've done an outstanding job with their results posted at their Ballistics by the Inch.com.
These gentlemen used a Thompson-Center Encore pistol as their platform and commissioned a gunsmith to make 18-inch barrels in various calibers. From there, after each round of testing, the barrels were cut back by one-inch, recrowned and returned for the next series of tests. This gives us direct comparisons based on the same barrel with the same characteristics as the previous length.
It takes a little more work than just reading their charts to understand the data, however. For instance, how much do you lose by choosing a 3-inch concealable 9mm pistol over a 4-inch "service" pistol? The answer, depending upon cartridge ranges from 99 fps to only 49 fps. The average is 69 fps.
Think your .40 S&W round is plenty no matter what barrel length you're using? If you're using Cor-Bon's 135 grain JHP, you're losing a whopping 100 fps per inch (103 to 138 fps) between a 5-inch barrel and a 3-inch tube.
This type of data is there, but you still have to work it out on your own. The good news is that you can directly cut and paste their data tables into a spreadsheet like Microsoft Excel. That allows you to crunch your own numbers if you're familiar with spreadsheets.
In preparing this article, I used Excel to help analyze some of the data. Since we're handgun oriented, I focused on the two to six-inch barrel figures. When I looked at .38 Special data, some intriguing things stood out. Something unexpected.
It seems that the losses when dropping from a 4-inch gun to a snubby 3-inch or 2-inch are much higher than losing an inch between four and five inches. In fact, for the ammo listed, the drop from a 4-inch barrel to the shorter barrels was the highest loss of velocity. This indicates that revolver cartridges are optimized for 4-inch and longer barrels.
Most surprising to me was that some .38 Special cartridges actually gained velocity when the barrel was cut from 6-inches to 5-inches! Both Cor-Bon 110 and 125 grain loads showed this behavior. Now, this could be some quirk of the barrel used, or it could be some odd error with the chronograph, but it remains interesting. Overall, the least loss in the .38 Special occurred by cutting a six-inch down to five-inches. Makes me appreciate my 5-inch S&W Model 10 just that much more.
Check it out for yourself. Look up your favorite cartridge and see what you're giving up by using that shorter barrel. Or perhaps you'll find you won't lose very much velocity by moving from that 5-inch Gov't model to a 4-Inch Commander. They've listed the sixteen most popular calibers, including .357 Sig, 10mm, .41 Magnum and .45 Colt. Even the new .327 Federal Magnum is included.
Your comments are welcome: editor@handgunclub.com
