Measuring muzzle velocity precisely

[Joe R]

Hi Guys,
I have a Oehler 35P chronograph and I have been measuring velocity in a bit of a sloppy manner. I generally set up the chronograph up about 15-20 feet in front of the bench. Obviously the recorded velocities are not actual muzzle velocities, some kind of mathematical adjustment needs to be made for that distance that I haven't been taking into account. Can anyone help?

Your help is appreciated,
Joe

 

[roadkill61]

Go to any ballisitic programs and ask for the output in 5 yd increments. Then you will now how much it slowed down in 15-20 ft and just add that on.

 

[jrbet83]

JBM ballistics gives you the ability to input your MV as well as your distance to your chronograph. Not to mention your chronograph isn't accurate enough for the 15'-20' drop in velocity to matter. What I'm saying, is the bullet "might" drop 5fps in 15-20', but your chrono is more likely reading more than a +/- 5fps reading than actually bullet velocity anyways.

 

[Joe R]

Thanks for the response guys, I appreciate your help and guidance.

Joe

 

[stool]

MARK THE CORDS AT 10, 12 15 FT....SET UP FROM THE END OF YOUR MUZZLE...

EASY TO GET IT RIGHT

 

[hogpatrol]

One word: Magnetospeed. It gives velocity six inches out from the muzzle.

 

[stool]

that is 1/2 of a foot off the muzzle...SO STILL NOT MUZZLE VELOCITY........
the 35p is nice in that it gives you 2 sets of velocity per shot...easier to back up to the muzzle velocity , in my opinion.

One word: Magnetospeed. It gives velocity six inches out from the muzzle.

 

[Joe R]

hogpatrol said: One word: Magnetospeed. It gives velocity six inches out from the muzzle.

Well, I would if I didn't already have a Oehler. It sure is a lot easier to setup.

 

[GaryCrow]

1 fps loss per foot is a good rule of thumb so if your chronograph is 15' in front of the muzzle then add 15 fps to correct for muzzle velocity. Obviously it's not exact, but it's close enough for government work. If you need it more precise than that it'll take something better than our consumer grade chronographs to measure.

 

[Catfish]

Why are you that worried about it being closer? I also have a 35 and set it roughly 15 ft. out and go with the read velocity to compute drop charts and have never found it to be a problem. Most drop charts will need tinkering with in the field to keep them on target if you go much past 600 yards. That and temp will effect velocity more than 15 ft. with a lot of powders, and even your extreme spread will be more than the velocity loss in 15 ft.

 

[mikecr]

Another thread about it:
http://www.longrangehunting.com/forums/f19/true-muzzle-velocity-61081/