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09-25-2017, 06:23 PM
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Velocity Difference
I have an sd9ve with a 4” barrel and a shield with a 3.1” barrel. Shooting the same ammo from each shows about 50fps lower on the shorter barrel. Getting about 900 on the sd and 850 on the shield. Would that be typical difference? Shooting 145gr lrn with 3gr Titegroup. Thanks
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09-25-2017, 07:03 PM
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You can figure to lose 25-30 fps per inch, but that's a very coarse guide. What is an sd?
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09-25-2017, 07:33 PM
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There are many websites which discuss such things and provide experimental data.
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09-25-2017, 07:39 PM
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Besides length, the barrel itself can make a difference. And at these lengths powder choice can as well. So given the same ammo, there's at least 3 factors that could be contributing to the difference.
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09-25-2017, 08:11 PM
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What Twoboxer said.
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09-25-2017, 08:47 PM
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Dunno what powder/bullet you are using, but being bored decided to run some stuff through Quickload. The loads below assume COL=1.12:
115gr PRN, Bullseye at max pressure, 4.0"=1247, 3.1"=1170, ie 77fps diff
115gr PRN, HP38 at max pressure, 4.0"=1186, 3.1"=1121, ie 65fps diff
These loads were chosen to generate ~900fps from a 4.0" barrel:
115gr PRN, Bullseye 3.4gr, 4.0"=907, 3.1"=840, ie 67fps diff
115gr PRN, HP38 3.5gr, 4.0"=895, 3.1"=828, ie 67fps diff
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09-25-2017, 09:42 PM
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There is typically 25-50 FPS per inch of barrel, usually closer to 25. That said, there are other differences that may allow the shorter barrel to actually be "faster" than the longer barrel. I have at least two 4" S&Ws that are actually faster than 6" S&Ws that I own, when shot the same day and with the same ammunition! You will only know if you buy a chronograph and do the testing yourself!
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09-25-2017, 09:44 PM
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Wait til you find the load that shoots FASTER in the shorter barrel 
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09-25-2017, 10:18 PM
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Even two guns.....
Even two guns of the same make and model can show large differences with the same load.
There is an article in my old Speer #9 manual called "What makes ballisticians get grey". They shoot the same loads out of a list of guns, many of them similar make and model. The results vary widely.
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09-25-2017, 11:58 PM
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"I have at least two 4" S&Ws that are actually faster than 6" S&Ws that I own"
For revolvers, anything is possible. Differences in the barrel-cylinder gap width can make as big a difference in MV as different barrel lengths. Not difficult to imagine that a 6" barrel with a wide gap may produce a lower MV than a 4" barrel with a tight gap with the same load.
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