Barrel Length and Velocity, Energyand Mid-Range Trajectory

[dougk]

For discussion lets use a Dan Wesson model 15 that has the interchangable barrels in 2.5 inch, 4 inch, 6 inch, 8 inch, 10 inch and the big boy 12 inch in .357 mag.

Will the differnt barrel lengths change the velocity, energy and mid-range trajectory (50 and 100 yards) using the same bullet?  Is there a study of barrel length affecting these items?

Thanks,
Doug

[Vern Humphrey]

Your average gun mag will run a story on barrel length versus velocity about once a year.

Generally, an inch of barrel represents from 25 to 50 fps.  A max load for a 158 grain bullet (according the the Hodgdon Manual) is about 1400 fps.  That's from a 7" barrel.  They don't say, so I suspect it's a pressure barrel, not a revolver.  That would make it equivallent to about a 5 1/2" revolver barrel.

In that case, your 3 1/2" barrel would develop about 1300 fps, the 4" barrel would be slightly faster, the 6" right around 1400+, and the 8" about 1500+.

The 10 inch barrel might churn up 1600 fps, and the 12 inch reach 1700 fps or a bit more.

Now, how this would prove out in any particular revlover is unknown -- differences from gun to gun might cancel out the difference to be expected from a couple of inches of barrel, more or less.

Trajectory changes would be minimal at the ranges you mention.  Recoil, however, would be significantly changed, and you would have different sight adjustments.

[CB900F]

DougK;

Here are some real-world numbers for you.  Numbers provided by the Oehler 35P.

Load:  4.5 grains of 700X, 125 grain Berry bullet, CCI standard primers.
6" barrel, mean 892 fps, SD 29
4" barrel, mean 862 fps, SD 54
2.25" barrel, mean 790 fps, SD 13

Load:  5.0 gr 700X, 125 Berry, CCI std
6" bbl, mean 947 fps, SD 52
4" bbl, mean 897 fps, SD 26
2.25" bbl, mean 859 fps, SD 25

Load:  14.2 grains Blue Dot, 125 grain Speer HP, CCI std
6" bbl, mean 1515 fps, SD 12
4" bbl, mean 1422 fps, SD 12
2.25 bbl, mean 1342, SD 55

Load:  Remington Golden Sabre 125 grain factory
2.25" bbl, mean 1083, SD 28

You may draw your own conclusions.

900F

[Savage]

As CB900F illistrated so well the powder burn rate is also a factor. With a really fast powder, it is possible that a longer barrel might produce slightly lower velocties than a shorter one. There is no absolute rule of thumb. The chrono tells the tale!
Savage

[Greybeard]

There really are too many variables for generalizations to work. Revolvers are the worst.

Cylinder gap to barrel affects velocity. The barrel affects velocity in more ways than one. So changing a DW barrel for a longer one can actually result in a decrease in velocity if the cylinder gap is set looser on the longer barrel and IF that longer barrel is one of those "slow" ones or the shoter is one of those "fast" ones. The internal dimensions and wear on the barrel matter.

The generalization is that a longer barrel will increase velocity up until you get to the point of ridiculous in barrel length. Different rounds have different barrel lengths where the change over will take place. In a .357 Magnum you still will be increasing velocity to that max DW barrel length. BUT those other factors might at some point make the next step up in barrel length not be an increase.

As to mid range trajectory there will be darn little and no noticeable different in moving from any one of those lengths to the next one up or down. From the shortest to the longest a noticeable difference is most likely to occur.

[leverfan]

My Speer Manual has a great article, titled, "Why Ballisticians Get Gray."  It explains the differences between different revolvers (or, in your case, different barrels on the same frame).  The article happens to focus on the 357.  The results are posted for 125, 140, and 158 grain loads, and it's simply too involved to compress the data here.  You could average the data and get some ballpark figures, but there's just no substitute for using a chronograph.  If you can come up with the dough for a Dan Wesson and 6 barrels, one of the inexpensive chronographs should be within reach.

In American Rifleman, they took a 44 mag revolver with an 18 inch barrel and shortened it in 1 inch increments.  I kept a copy of their chart, the last time it came out.  Velocity change per inch ranged from a low of 11 fps to a high of 193 fps.  In a barrel that's over 9 or 10 inches, they lost only about 30 fps or less per inch chopped off.  Once the barrel got shorter than that, the loss of velocity that accompanied each lopped off chunk of barrel increased sharply.  Going below 6 inches in length for the 44 mag really made a difference.  3 different 240 grain loads were used in the test, so the velocity loss is an average.