Hi Guys.. does anyone have any velocity figures for mag -tech .38 special fmj flat point ammo out of an M&P 340?

Information regarding velocityes a particular handgun will deliver is specific to firearm as even several different handguns of the same manufacture and barrel length may vary as much as +/- 10%.

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and subtract 100 fps from the velocities listed for a 4" vented test barrel to get an approximate velocity from the 2" snub nose +/- an expected variance from the particular handgun.

Thank you for the information Steve.

The velocity change per inch of barrel length can vary quite a bit for different propellants, and also the length of the barrel - that is, the velocity change per inch will be different from 10" to 8" vs. 6" to 4". It is not a constant. Typical will be 40-50 fps/inch but it could be more or less.