Ballistics by the inch

How long is too long?

We’ve long known that many pistol calibers/cartridges are optimized for fairly short barrels — you see real benefits in increasing barrel length out to 6″ or 8″ or so, with diminishing returns beyond that. (The exception to this is the ‘magnum’ rounds: .44mag, .357mag, etc.) It’s not that you don’t see any benefit in a longer barrel, but the gain tends to flatten out. Take a look at the muzzle energy graph for the 9mm Luger (9×19) and this is quickly apparent:

Take a look at the left side of that graph. There’s some indication that the bullets are actually slowing down in the last couple of inches of an 18″ barrel. Whether or not this is just a glitch in our earlier test data, or an indication that friction is starting to win out over the remaining energy from the expanding gas of a fired cartridge is something I’ve always wondered about. Clearly, at some point a bullet will start to slow down, even stop; anyone who has ever fired a squib load and had to hammer the bullet out of a barrel knows that this can indeed happen. But at what point would this effect start to be clear?

Good question. And not one we really wanted to spend the money on to find out. See, the barrel blanks we’ve used all along came in an 18″ length standard for pistol calibers/cartridges. Longer barrels were available from different sources, but there was a big jump up in price for those, and it just didn’t make much sense to get into that.

However …

When we started to set up to do the so-called “Glock Tests” we had to find a different source for our barrel blanks, since our other supplier couldn’t provide a polygonal barrel (the kind of barrel Glock uses, though they are not unique in this). We sourced the barrels from Lothar Walther. And as it turned out, their barrel blanks are longer than 18″. Specifically, we received a 26″ barrel with traditional land-and-groove rifling and a 24″ barrel with polygonal rifling. Here they are:

9mm barrel blanks

9mm barrel blanks

So …

Well, we didn’t want to spend the time and money doing full chop tests from 26/24 inches down to 18″. But we did decide to just go ahead and get some benchmark data at the full length, just for shits and grins. And here is the data for those lengths, along with data from 18″, 17″, and 16″ lengths for comparison:

PNW Arms STD P 115gr SCHP

Trad:    1074 fps     1161 fps     1163 fps     1171 fps
Poly:    1064 fps     1131 fps     1131 fps     1135 fps

Federal STD P 115gr Hi-Shok

Trad:     1305 fps     1330 fps     1333 fps     1330 fps
Poly:     1323 fps     1331 fps     1336 fps     1135 fps

CorBon +P 115gr DPX

Trad:     1117 fps     1232 fps     1249 fps     1236 fps
Poly:     1057 fps     1186 fps     1195 fps     1208 fps

Black Hills +P 115gr JHP

Trad:     1494 fps     1508 fps     1512 fps     1498 fps
Poly:     1496 fps     1521 fps     1515 fps     1518 fps

Federal STD P 147gr JHP

Trad:     1036 fps     1061 fps     1084 fps     1085 fps
Poly:     1046 fps     1088 fps     1098 fps     1088 fps

So, there ya go: in each and every case, there is a noticeable decrease in velocity in going from an 18″ barrel to either the 24″ or 26″ barrel. And keep in mind that the protocols for this test were 10 shots of each ammo at each barrel length over two chrono units, rather than just 3 shots as we had done for previous chop tests.

Not too surprising, but nice to see actual data.

We hope to have the full data sets, with charts & graphs, up on the website soonish (maybe next week?). Watch here and on our FaceBook page for a posting when it is available.

 

Jim Downey

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October 11, 2013 - Posted by | 9mm Luger (9x19), Anecdotes, Data, Discussion., General Procedures

5 Comments »

  1. […] as discussing it with people online and with the other BBTI members when they were here for the recent tests (one of whom has been a Glock armorer for 15+ years) a couple different strategies emerged for me […]

    Pingback by Now, about those thunderbolts… « Ballistics by the inch | October 15, 2013 | Reply

  2. MOST Excellent!
    Looks like the PCC weapons are pretty optimized for the Pistol Calibers they serve, in most cases…
    Everything I shoot is not worth the effort to find a longer barrel than 16″. GREAT INFO, BBTI!
    I use your posted data a lot!

    Comment by R Greene | February 13, 2014 | Reply

  3. I have an interesting pistol caliber conversion that is a custom. In working up loads with a chrono and
    various powders it occurred to me, that pistol powders are DESIGNED to be burned in shorter barrels.
    … So… what if you went to a slower burn powder, that would ‘push’ longer. I’m currently working with
    2400, MP-300 and such, for .44mag, 45ACP, and 50AE in 18″ barrels.
    I’m seeing 1700-1950 fps for the first and last of those. Thumpers. primers looking ok.

    Comment by dancowan | October 13, 2014 | Reply

    • That makes perfect sense, dancowan, and is basically turning those cartridges into rifle rounds. The one thing you’ll need to watch is not mixing that ammo into ammo you use for your handguns, where the performance will be much worse.

      Be safe, and be sure to share your results with other reloaders when you feel comfortable that you’ve worked up safe, effective loads!

      Thanks!

      Comment by James Downey | October 13, 2014 | Reply


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