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Old June 2, 2005, 10:27 PM   #1
YosemiteSam357
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Velocity loss, 4" ported vs. 6", 44 mag

Can someone tell me the approximate velocity, energy, and/or pressure loss I'll see in a 4" ported barrel 44 mag vs. a 6" barrel? Most of the loads I've seen published (and I admit I haven't looked far at this point) use a 6" test gun, if not an 8". I'd really like to be able to calculate the numbers for my 4" using the supplied 6" or 8" data. Is there a formula that can be applied?

Thanks in advance,

-- Sam

P.S. I don't own a chrono.
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Old June 4, 2005, 03:15 AM   #2
WESHOOT2
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theory vs reality

I have two 4" 357's, a 5.5" and a 7.5".
Testing reveals they have distinct performance behavior.

My point?
Regardless of barrel length, or action type, or wishing, the only way to know is through testing; no exceptions.
None.

(See, you get yer cylinder dimensions, then yer cylinder gap, and next the forcing cone, then barrel bore. You got different test environments, different measuring tools, and mebbe some other stuff. There's a section in Speer's manual about "Why Ballisticians get gray", because they got no formula....and I've chrono'ed enough guns with matching-lot ammo to at least 'guess' a little better; I guess I don't know unless I chrono. Ay?)
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Old June 4, 2005, 08:24 AM   #3
Mal H
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... and Tim's final point goes double when talking about revolvers. There are so many variables that the velocity achieved in one revolver can be hundreds of FPS different from a revolver of the exact same brand/model with the same barrel length.

The best way to see what happens is to find someone with a chrono (or borrow/rent one) who would be willing to help with your experiments.

However, if you want some ball park figures only (and it's a big ballpark), subtract 50 to 100 fps for each inch and subtract an additional 5% for the porting. So, using 1200 fps in a 6" barrel as an example, you lose 100 to 200 fps for the barrel length and about 50/55 fps for the porting = roughly 950 to 1050 for that round.

YMWV.
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Old June 4, 2005, 02:30 PM   #4
YosemiteSam357
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Ok, that answers that. Thanks!

-- Sam
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Old June 4, 2005, 06:25 PM   #5
WESHOOT2
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as long as yer sawin' on the same barrel

That 'formula' has been working fairly well since speeds got measured, but do not take it as gospel; consider it 'hypothetical'.

If you're anywhere near my way stop in and we'll chrono......
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Last edited by WESHOOT2; June 4, 2005 at 06:27 PM. Reason: still remember friend buying 6" 45 but it was slower than his 5" 45.....
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Old June 5, 2005, 05:02 PM   #6
Mal H
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By the way, Sam, here is some good reading on the subject by Lee Jurras: http://www.leejurras.com/barrellength.htm

Note he did what WESHOOT2 mentioned, he sawed down the same barrel instead of trying to extrapolate what loads would do in guns with different barrel lengths. Even then, you'll see that some rounds got higher velocities out of a shorter barrel. Lot's of variables at work there.
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Old June 5, 2005, 06:50 PM   #7
Sturm
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Short of using a hacksaw, there have also been a number tests conducted with Dan Wessons that arrived after Lee Juras' testing. The pistol packs gave you 2.5", 4", 6", 8" and 10" barrels and add Layne Simpson of "Shooting Times" to the list of testers. Velocity will vary in identical revolvers/pistols due to varying tolerances in machining from the same manufacturer and the same model within the tolerance range. Reducing barrel length will reduce velocity and porting is similar to a reduction in barrel length, especially the Taurus variety that uses an expansion chamber with the porting. True barrel length stops where porting begins. What doesn't change in barrels as short as 2", is pressure, because it has peaked before the 2" distance has been reached, but not in the cylinder as many have stated, including a fella in this thread, pressure peak is not achieved until a bullet has been restricted by a barrels rifling.

Because of differences in tolerances with chambers, cylinders and land/groove diameter, there is not an absolute value. Very little is absolute, but there is a thing known as "Rule of thumb" and I believe that Simpson found 80 FPS +/- velocity loss with each 1" reduction of barrel loss from his test conducted with Dan Wessons. If a barrel is ported, reduce barrel length another 1"!

Not absolute, but worth knowing, as is the fact that velocity loss and MUZZLE BLAST can be controlled better through the proper selection of pistol powders when using shorter barrel lengths, under 4" in particular. Chrongraphs come in very handy when weighing such oppinions/theories/hypothesis!
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