[time-nuts] A real-world precision timing need....

[scmcgrath at gmail.com]

Initial suggestion would give muzzle velocity only - need coffee before commenting

A piezo detector bonded to the plate would give time of impact.   I'm interested in how you would compute group size 
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-----Original Message-----
From: scmcgrath at gmail.com
Date: Mon, 1 Nov 2010 11:57:43 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: scmcgrath at gmail.com
Subject: Re: [time-nuts] A real-world precision timing need....

Why not purchase one of the existing ballistic chronographs and upgrade the time base?


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-----Original Message-----
From: Bob Camp <lists at rtty.us>
Sender: time-nuts-bounces at febo.com
Date: Mon, 1 Nov 2010 07:49:06 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] A real-world precision timing need....

Hi

The original request was to measure both velocity down range and time of flight. They certainly are related, however the relation (especially around the speed of sound) is difficult to estimate. If you are dealing with a projectile that drops sub-sonic as it goes down range, velocity is indeed worth checking. 

-------------

If you own the range (800 yard range in the back yard hmmm...): 

Head over to the local cable TV outfit's scrap yard. Pick up a spool of what ever they are throwing away. Dig a trench and burry some out to each observation point. Coax in the ground is going to be much more stable timing wise than  anything else you can get for free. With it buried it will last a bit longer than wire on the surface. 

Bob

On Nov 1, 2010, at 1:37 AM, Mark J. Blair wrote:

> 
> On Oct 31, 2010, at 7:21 PM, Bob Camp wrote:
>> The gotcha is that the gong can move / twist when hit.  The plate buried in front of the electronics has to just sit there and take it. More energy transfer to the anchored plate. 
>> 
>> I'm sure there are alloys that will get you under 1", the issue will be making sure you have the right one...
> 
> Ah, good point. Also, it won't matter if the steel stops the bullet from penetrating if the shock turns the enclosed electronics and optics into powder.
> 
> As an aside, when I bought my high power rifle rated steel gong target (which, sadly, I haven't taken for a test drive yet), I looked at pre-shot samples from about four different vendors who had displays at the gun show, and there was a noticeable difference in the steels that they used. The vendor I chose had little more than faint dimples surrounded by lead spatters where .308 rounds allegedly hit their target, while other vendors had substantial craters.
> 
> Back to the topic at hand: If muzzle velocity and time of flight alone would provide enough data (*), then one possibility would be a downrange target with an attached transducer (piezo?) to register the bullet impact, with a wire pair going back to the shooting bench. In this case, the downrange sensor would be cheap to replace when it eventually fails, and all of the expensive/delicate stuff would be back at the shooting bench.
> 
> (*) I haven't studied ballistic equations carefully enough yet to know whether this would provide enough information to estimate fun details like ballistic coefficient.
> 
> 
> 
> -- 
> Mark J. Blair, NF6X <nf6x at nf6x.net>
> Web page: http://www.nf6x.net/
> GnuPG public key available from my web page.
> 
> 
> 
> 
> 
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