Velocity Decay from Chronograph to Muzzle

[DocUSMCRetired]

Muzzle Velocity Decay between Muzzle and Chronograph.

Did you know, the difference between your chronograph and the muzzle can make a sizable error in your firing solution? An error of 10 fps can equal an error of 5" or more at 1000 yards. More than one factor goes in to correcting for the distance between your muzzle, and your chronograph. Including atmospheric correction. All chronographs begin measuring the bullet, after it leaves the muzzle, so you must correct for the distance between. No chronograph is exempt from this, even the MagnetoSpeed is 1 foot away from the muzzle at the time of measurement. Chronographs measure velocity at their specific location, not Muzzle Velocity. To learn more check out this short article on adjusting for your Chronograph to Muzzle distance.

http://www.appliedballisticsllc.com/Articles/ABDOC121_VelocityDecay.pdf

If you have ever had a small error in your firing solution, knowing this simple bit of information can sometimes help you track down and remove that small error. This is just one of many small adjustments a shooter should check when the live fire, and the predicated solution don't line up.

 

[Ned Ludd]

The far end of the MagnetoSpeed sensor deck is approximately 6-7" away from the muzzle, tops. The magnitude of the effect at that distance on measured velocity as compared to true muzzle velocity isn't even worth considering as it's less than 1 fps and well under the error rate of the device.

 

[Mozella]

My cheap Caldwell lets me input the distance from the muzzle and other data so that it can read both velocity as the bullet passes over the sensors and also calculate the true MV. A quick look at the chart produces a correction value which is equal to the value calculated by the Caldwell app.

 

[mac86951]

My cheap Caldwell lets me input the distance from the muzzle and other data so that it can read both velocity as the bullet passes over the sensors and also calculate the true MV. A quick look at the chart produces a correction value which is equal the the value calculated by the Caldwell app.

Same with my ballistic calc. I have a calibrated string to make range set-up easy for the right distance from the muzzle.