Coated bullets and the chronograph...

[JRose]

Does anyone else have trouble when trying to chrono coated bullets? It seems like the chrono doesn't like to read the coated bullets (BN), but never misses a lick with uncoated.

I might get 1 out of a 5 shot string that will read...

 

[our gang]

Re: Coated bullets and the chronograph...

You're probably not getting enough reflectivity (my new word) off the bullet as it passes over the Chrony windows. You might try shining a couple of incandecent lights up from the bottom, while covering the top light source.

 

[Rafael]

Re: Coated bullets and the chronograph...

Is there a chrono that uses reflectivity?
I am not aware of any.

All those I know of use light interruption.
Light above, sensor below.

Is this the first time you had a problem getting readings, or has it happened the same way with both coated and uncoated on different days? If just the one time for the coated, I would blame the days lighting conditions.

 

[Victor N TN]

Re: Coated bullets and the chronograph...

+1 for RAF...

 

[MLC]

Re: Coated bullets and the chronograph...

My chrono had no issue picking up 30 hBN coated 308's on Thursday.
It was between 3:30 and 5 pm in cloudy weather.

 

[Saito]

Re: Coated bullets and the chronograph...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mr. Humble</div><div class="ubbcode-body">You're probably not getting enough reflectivity (my new word) off the bullet as it passes over the Chrony windows. You might try shining a couple of incandecent lights up from the bottom, while covering the top light source. </div></div>

Light coming off of the bullet doesn't have shit to do with it. Light above the screens is important as the chrono "sees" differences in light and times one difference to the next as your bullet passes each screen. I need to call the Chronograph people and ask them to make the plastic for the screens out of glow in the dark material so it would be more of a contrast as your bullet passes through. Maybe you could even use it in the dark?

 

[JRose]

Re: Coated bullets and the chronograph...

Well, this is the second time I've used it (borrowed from a friend), and results are the same. Both days were slightly overcast, but I'm using the IR screens that are supposed to negate the amount of light needed by the stock screens. The instructions state that, theoretically, you can chrono at night using the IR screens...

BUT, I'll be damned if every time I shoot shinny uncoated bullets I get perfect readings, but when I shoot coated bullets, I'm lucky to get one or two that even read...

Aggravating....

 

[JRose]

Re: Coated bullets and the chronograph...

Way off base with this?

 

[Rafael]

Re: Coated bullets and the chronograph...

I don't think so.
Hard to say what the problem is since the bullets shadow is the only thing that matters. Since you did not change the bullet profile, I can't imagine what the problem is.

 

[JRose]

Re: Coated bullets and the chronograph...

The only other difference is that the uncoated bullets where .308, the coated were .243.


If the coating is a problem, is there anything I can do to make it read? I really need to get this data...

 

[Rafael]

Re: Coated bullets and the chronograph...

Aha, more data!

There is enough difference in size that you could have been on the border of "enough" light. Also, the 308 may have been set up lower than the 243 in relationship to the screens.
I would suggest improving the lighting situation, cleaning the lenses on the chrono, and trying to keep the shots down closer to the sensors.

In the average chrono, there is a pie shaped viewing area for the sensors. The lower the bullet passing by, the larger the cross-section of light they interrupt. Lower appears bigger.

 

[btm_54]

Re: Coated bullets and the chronograph...

Have you tried putting a ring on the bullet olgive where it does not touch the barrel with a sharpie. That might help.