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Old January 11, 2011, 06:31 PM   #1
Biff Tannen
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2" vs 4" ballistics for 3" barrel?

I'm currently carrying a derringer with a 3" barrel, chambered in .38 / .357.

QUESTION- IF reliable ballistics for a certain ammunition are only available for either a 2" or 4" barrel, which should I go with for my 3" barrel?

THANKS!
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Old January 11, 2011, 06:52 PM   #2
Mello2u
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http://www.ballisticsbytheinch.com/
The above website might have some info for you.

Every barrel is unique. You can only generalize about external ballistics when thinking about barrel length. You posts begs the question of what is "reliable" information. Unless you actually chronograph your particular handgun with a particular load, you will never know.

The various factors of a barrel other than length which may effect bullet velocity (that I can think of off the top of my head) are: bore smoothness, uniformity of diameter of the bore, depth of rifling, type of rifling, barrel to cylinder gap (if any), free bore (if any), and twist rate of rifling.

In general I would consider the 2" barrel ballistics and be happy if you actually got any real increase. In a short barreled handgun a few % increase or decrease in velocity is not all that important.
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Old January 11, 2011, 07:01 PM   #3
Biff Tannen
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Mello2u
Good advice... Sounds like what you are saying is, utilize any credible ballistics as a guideline, until I can test it out with my particular setup. Similar to a science experiment, where you have a control group and an experiment group, use the ballistics as the control group, and my gun as the experimental group.
Also, I agree with the logic of your philosophy when you say "consider the 2" barrel ballistics and be happy if you actually got any real increase." Good thinking!
THANKS!
PS- Appreciate the link!
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Old January 11, 2011, 07:17 PM   #4
jhenry
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The barrel length measurement for a revolver is made from the muzzle to where the barrel terminates at the cylinder gap. It does not extend to the breach face. For your derringer (and for semi autos) the barrel length measurement goes from the muzzle all the way to the breech face. In other words, for a revolver it covers the actual barrel, for other types it covers the barrel as well as the chamber.
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Old January 11, 2011, 08:01 PM   #5
Kreyzhorse
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Quote:
In general I would consider the 2" barrel ballistics and be happy if you actually got any real increase. In a short barreled handgun a few % increase or decrease in velocity is not all that important.
Very sound answer and well put. +1.
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Old January 11, 2011, 08:18 PM   #6
Biff Tannen
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jhenry,
Okay... Please correct me if I'm misunderstanding...
Are you saying that, when I'm looking at ballistics from a revolver and making comparisons to my derringer, a more accurate comparable measurement of the derringer barrel is the given factory "barrel length", MINUS the length of the round? Or am I missing the point completely?
Thank you!
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Old January 11, 2011, 09:22 PM   #7
jhenry
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You are correct. The revolver does however loose a tad bit of velocity due to cylinder gap, but not as much as many think. For the short barreled stuff I think the cylinder gap does not matter at all in practical terms.
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Old January 11, 2011, 10:07 PM   #8
Biff Tannen
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Jhenry:
Did you ever have a moment that you realized a fact that made so much sense you were ashamed you didn't understand it a moment prior?!
THANK YOU... And so, the conclusion is, that with a 3" derringer barrel chambered for 38/357, the ballistics most relevent are that of a 38/357 revolver snubbie (unless, of course, the derringer ballistics are offered)! Case closed with Godspeed! (unless there are any last minute "dark horses" with additional gems of wisdom/insight/advice)...
Thanks again, all!
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Last edited by Biff Tannen; January 12, 2011 at 12:24 AM.
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Old January 12, 2011, 10:00 AM   #9
rodfac
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Biff...the pic below shows some testing I did last summer, shooting into a swimming pool. The tests were done with my wife's S&W 637-2 to test relative expansion of various .38 Special +P loads. All loads were chronographed and the velocities shown were the average of 5 shots at 12' screen distance. The revolver used has a 1-7/8" barrel (virtually the same as your derringer.)

Also, one bit of caution, factory velocity data is often optimistic to say the least and is affected by the length of the test barrel used. Individual guns vary as to velocity, of course, but the data I've included here was chrono'd by me in my guns, on a hot KY day.

BTW, the Federal 129 gr JHP Hydra-Shok +P Tactical load chrono'd 840 fps from the 2" barrel. (Forgot to add it to the pic captions.) This same load chrono'd 951 fps from a 3" Chief's Special .38 Sp. The 3" barrel produced 921 fps with Remington's 125 gr .38 Spl +P JHP factory load.

I don't have the velocity of the Winchester 125 gr Silver Tip JHP +P bullet.

Before anyone get's their skivvies in an uproar, I'm well aware that the water expansion medium does not equate to human flesh and bone. I used the pool because it would allow me to have the same medium for all shots, and allow recovery of the spent bullets as well as offer a look at comparative expansion.

I've posted this photo before...hope it helps...Rodfac

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Old January 12, 2011, 03:46 PM   #10
Biff Tannen
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Rodfac:
I find great value in water tests, in that they allow obgective and controlled comparisons of mushroom and expansion potential.
Thanks much for sharing, and for your advice!
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