Hey guys what is everyone's opinion on this. If you have your chrono set up close do you think there is a chance of damaging the chrono. Lets say 3 ft from the muzzle with a 7mm mag. Thanks for the input.

I think the bigger danger is that you get bad readings as the chrono reads the shadow of the gases, etc. rather than the shadow of the bullet.

I seem to recall setting mine up a little too close (way more than 3 ft., though!) and getting a couple of readings in the 8000 fps range from a .30-06.

John

I've knocked mine over having it too close to a boomer. It was about 8 ft. away. Now, it is set up about 10-12 ft. Seems to work fine, so far. - Dan

I've never got any screwy readings but I did blow the skyscreens and rods all over though and that was about 3 ft from the muzzle. Since then I too have moved mine a little bit further downstream too!

I`ve never had trouble with mine when too close with a rifle except to wobble the screens. My pistol will sometimes cause it to act up a bit.
I have had the guy on the next bench screw my readings up shooting a mag with a muzzle brake. Nothing like haveing to edit every other reading while trying to concentrate on your shooting to get old fast!

If the gasses interupt the reading then there is no point in having it that close. With rilly big guns I'm shore you could do some damage. For instans, I've herd of people geting knocked off there feet form the muzzle blast form a 50BMG when they were 15feet away.

Whatever the distance from the muzzle to the start screen, when the muzzle velocity is slower than the speed of sound (handgun loads, for example), the muzzle blast can affect the accuracy of your readings. The blast can trigger the start screen before the bullet gets to it. Not good if you want accurate data.

The solution is both simple and easy, and it helps tame the blast from the big boomers too.

Set a plywood baffle between the muzzle and the chronograph, with a hole or vertical slot just big enough to aim and shoot through. A two-foot or larger square of 1/2-inch plywood, with a prop on the far side, or a good solid base, is all you need.

I always just set my chrongraph up at 12-15 feet. Farther away for the magnums. This really only represents an underestimate of 20fps or so. The Beta Chrony has a 16 foot cable and allows you to set up 12-15 feet away. Whenever I get closer than about 10 feet with the magnums I get readings like 425fps. No problem just move it farther out.

There are two types of chronograph owners. Those who shot their chronograph and those who haven't shot it yet!

[This message has been edited by grkldoc (edited 01-07-2002).]

[This message has been edited by grkldoc (edited 01-07-2002).]

The farther out you move your screens, the more adversely the muzzle blast can affect your readings when muzzle velocities are below the speed of sound (about 1,180 ft/sec, depending on air temperature).

Figure it out for yourself:
-- The bullet and the blast come out the muzzle essentially simultaneously.
-- The sound of the muzzle blast travels forward at the speed of sound. I hope this doesn't surprise anybody.
-- The bullet travels forward at muzzle velocity minus whatever drag losses reduce it.
-- If the muzzle velocity of the bullet is lower than the speed of sound, the bullet never catches up with the sound of the muzzle blast.
-- If the blast wave is violent enough, it can (and often does) trigger the start screen before the bullet gets there.

Use the baffle.

[This message has been edited by Ken Howell (edited 01-07-2002).]

I like the baffle idea, Ken. I'll rig myself up one this weekend. Thanks. - Dan

Concerning big bore calibers with muzzle break,I adjust the chrony 12 feet away from the blast,I use a Masters Tripod{Baush & LOMB}60",the tripod works fine...

I have no problems at 12", except one time when I centered the chronograph with a 180 gr. at 3000 FPS and that threw things out of whack permanently.

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

Thanks for all the answers guys the baffle sounds like a good idea to me too.

I was having a lot of trouble with my pact model one this last summer. I had just bought a 300 WSM and couldn't get it to register. I was about to pack it up and send it to them, but found out they wanted prior notice, a phone call first. I called and they asked if I had the cables straight and seperated or all twisted together, and was I protecting the box itself from muzzle blast? I said no to both questions. Also he said to not have the screens closer than 15 feet to the muzzle of a magnum rifle.

Next time I set up, I went out to 15 '. kept the wires seperated and put the box on the next bench with a sandbag in front of it. It hasn't missed a reading since.

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if you run, you just die tired