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View Full Version : Chronograph Baffle Screen Use ...



John Boy
12-23-2008, 03:13 AM
Those 'ERR' readings on the chrono are getting to be a pain, so plan to start using a muzzle blast screen of 3/4" plywood ...
What are your experiences using one, specifically:
* How far in front of the muzzle do you place the screen?
* Have any statistics of fps reading variances with and without the screen?

montana_charlie
12-23-2008, 01:57 PM
What brand of chrono are you talking about? Just curious...
CM

martinibelgian
12-23-2008, 03:14 PM
In my experience, putting your chrono as far as possible (3 - 4 m in front of the muzzle should be enough) out will eliminate those pesky "ERR" readings. It will also reduce lube splatter of your skyscreens...

John Boy
12-23-2008, 11:37 PM
Charlie, it's the The F-1 Master Chrony. It works good for me with the screens out 12 feet. But when I see the muzzle blast traveling a 1000+ fps and then the readout goes ERR ... it's not rocket science that a baffle is needed. It's also factual that any part of the muzzle blast going through the screens is going to give inaccurate fps readings. So, from now on - there will be a 3/4" piece of plywood with a shooting hole in it. Thought maybe with the post I could 'go to school' on you fellas

Had the experience in the service jumping out of C141 - one time when the prop wash baffle wasn't working. Let me tell ya - ya get thrown all over the place from the wash. Has to be the same effect with a chrono ... readings that are not true

Gellot Wilde
12-24-2008, 06:01 PM
I've had the same problem with my F-1 Chrony, not ERR all the time just now and again, I wondered about some kind of baffle but wasn't sure if that was the prob....intresting to read your post.

montana_charlie
12-24-2008, 11:48 PM
Had the experience in the service jumping out of C141 - one time when the prop wash baffle wasn't working. Let me tell ya - ya get thrown all over the place from the wash. Has to be the same effect with a chrono ... readings that are not true
The sensors in a Chrony just react to light. When the bullet passes, the light changes and the front sensor makes note of it. When the same thing happens at the rear sensor, they compare notes to see how long it took for the bullet to pass between them.

Muzzle blast may be able to make the grass wave, or blow your hat off...but it doesn't change the light.

If you are blowing powder particles, or paper patch shred, bullet lube chunks, or loose gas checks past the sensors...along with the bullet... they might get confused. They get confused most easily when two objects go past the front sensor before anything reaches the rear sensor.
The way they spell confusion is "ERR".
CM

martinibelgian
12-25-2008, 04:13 AM
Ditto as to what CM says - it's chunks other than lead you need to avoid. With my PACT, I just put the skyscreens as far in front as the extension cord of the CPU will allow, and that usually cures the problem. Most 'debris' will usually not reach the skyscreens as they are much lighter and fall to the ground before reaching the screens.

montana_charlie
12-25-2008, 01:21 PM
And one other thing about chronographs...

You often hear reference to 'screens' or 'sky screens' and the comment usually seems to infer that the screen(s) do not 'sense' the bullet passage reliably.

On early chronographs, there were actual screens that the bullet had to punch through to be sensed as it passed. It was an 'impact' which was being detected.

On a Chrony, the 'screens' are simply 'simulated clouds'.
If you are shooting on an overcast day, the 'screens' are not needed. The 'shadow profile' of the bullet is easily seen (by the photocells down in the box) as it is silhouetted against the cloud cover. When shooting on a bluebird day, the screens come into play to provide the translucent white background for the bullet's silhouette.
'Sunshade' is a more useful descriptive term for those plastic pieces.

Other silhouettes, such as over-powder wads and powder fouling debris...as well as deer flies and honey bees...will also be detected as they pass between the 'screens' and the photocells.

Anyway, to say the 'the screens are placed 12 feet from the bench' gives an impression that the 'sunshades' are the elements that sense the bullet...and (being physically exposed as they are) are subject to all manner of damage that will be critical in detecting the bullet.
Actually, the photocells do that job, and are pretty well protected down in the box.

They just need to be kept clean to do their job...and the batteries need to be fresh.
Those two considerations will go a long way in eliminating the 'ERR' messages.
CM