OzFclass

Cross posted from Electronic Targets...


As far as we know, never before has it been possible to shoot from four firing points randomly at one target with the shot results being presented to the shooter who fired the shot.

At Canberra today a total of 526 shots were fired by 27 shooters on to two OzScore Electronic Targets from four firing points. We believe that this is a World First. It is the culmination of nearly four years of R&D effort here in Canberra, Australia.

All the virtual target images were available for viewing on a standard laptop browser in near real time (within 2 secs of a result determination). In 98% of cases, shooters are advised of the shot result within 1/5th of a second of impact time (often less than 1/10th second).

The range was 600M onto an ICFRA aiming mark. It was a Spoon shoot so the shots counted. About 200 were fired in a 2 FP to 1 TGT configuration with no apparent shot collisions at the target or misses attributable to a system fault. The remainder were shot from the 4 FPs to only one target - we deliberately took the 2nd target out of service simply to conduct this test. I'm not sure how many collisions occured possibly one. There was one "lost" shot due to a communications problem. I need to analyse the data to see if there were any bogeys I wasn't informed about - normally a shooter will complain bitterly when a fault occurs. But maybe they were being nice to me today.

We had a number of misses. All were accounted for due to non-zeroed rifles and were actually missing the target. But it had me on edge until this was confirmed. In fact, the target system adhered to my policy of giving the shooter some benefit of doubt by designating what was effectively a miss as a null (unscored) shot due to target fault (when it was in fact a bullet sailing over the top thus triggering the top but not bottom microphones). I need to revisit the logic associated with this.

There were two apparent cross fires detected. I think this was erroneous as only one target was being shot at. But the shot was measured and the result manually attributed to the shooter.

Given the complexity of this system - the only one apparently in the world that employs muzzle blast detection - that requires rather sophisticated software to manage all that is going on in real time, overall I consider the day to be a great success. I think everyone had a lot of fun - shooting did not cease until 4.45pm and I can't remember when we shot for over 3 hours without a break at Canberra.

I do not believe that shooting from 3 or more firing points at one physical target has ever been attempted before. If someone _is_ aware of an instance please let me know. During testing we routinely shoot 2 to 1 and it's almost boring. The design limit is 6 per target. I believe that the ADI system could do two back in the early '90's but that was before my time.

I will be analysing the data tomorrow in order to gain accurate and detailed statistics and will place these and other information (and photos) on the OzScore website as soon as I can (like tomorrow - Sunday 4th Sep). I will place a notice on this forum once I have it live to air, as it were, with the URL.

There are a few issues to resolve - all minor - and no show stoppers as yet.

If anyone is interested, a configuration of the OzScore such as we used today at Canberra (4 firing points on to 2 physical 1800x1800mm targets) would start at around $28K ex GST and excluding freight and installation costs. I think (and hope) my objective to make ET's [more] affordable for general small club and OPM use is close to being realised.

Sorry. I couldn't resist blowing my trumpet a bit.

Geoff Roberts
OzScore Target Systems.

sounds really good! how does the system work when one person is shooting 162gr a-max at 3200fps out of a 7mm SAUM and the next guy is shooting a 5.56 80gr at 2900fps?

There are a couple of caveats. One being (and probably the most important one) time of flight variations.

There is not much I can do to compensate for this.

The system provides an approximation of time of flight - +/- 50 milli-seconds. Approximate because the system overall is non-deterministic due to the nature of the Wifi and mound/target radio links.

It is, I suppose, possible for a bullet that is fired shortly after another, to actually arrive at the target first. With the current system it is hard for me to discriminate this. A future system will employ GPS time synchronisation that will keep the various computer clocks tied to within a few microseconds of each other. The OzScore target computer keeps an event time resolution of 1 millisecond. (Not to be confused with microphone time resolution. The microphone sampling frequency is 1/2 microsecond - or approx .66 mm maximum resolution. Note that this is in reality unattainable - I will have more on system errors and Areas of Uncertainty on my website).

Bottom line...

It is currently assumed that a shot fired first will arrive prior to a second shot. Measurments of ToF show that there is not really too much difference between the ToF of a .223 and .308 projectile. It depends on range of course.

For club use (for which there is a specific mode of operation) it was decided that balanced between cost of a bullet and that of a second target the occasional "error" (null shot) was acceptable. For competition perhaps not. I do not advocate multiple shooters per target for competitions at this time.

When a bullet passes through a target there are two time points that become important. One is the maximum time (worst case scenario) it takes for sound to diagonally cross the target. In the case of an 8'x6' target this is a bit over 8 mSecs. So if two bullets strike the target within 8 mSecs (or so) of the previous bullet, neither will be resolved as the second completely stuffs the readings of the first. However, when the first bullet strikes, in the OzScore a timer starts that ensures that sufficient time passes for echoes within the target to die down. I call this the "dead time" and it is currently 20mSecs on our 1800x1800 (6'x6') target. If the second hits _after_ the 8mSec sound transit time but before the end of the dead time (see below) then the first can be resolved, but not the second. We are still studying this - it is so rare that we are having difficulty matching theory with reality. Sorry about that...

If a bullet strikes _after_ the sample time of the first _but_ prior to the expiration of the 20mSec "dead time" it cannot be resolved, as the target is electronically disabled during this dead time.

20mSecs is 1/50th of a second.

So, in a multi shooter per target scenario it will be possible for this collision situation to occur. Maybe it is acceptable - maybe it is not. I do not make this determination. All I want/need to do is advise shooters of the likelihood... and they can make thier own decision as to whether or not it is acceptable.

Based on todays experiment, the probability is low. Not non-existent, but low. Today there was perhaps one instance in 500+ shots of a shot collision - and if it occured only the 2nd shooter was affected. And this was only when we were firing 4 to a target.

Statistically the collision can and will occur. We have yet to see what the reality is. Stay tuned! We will be shooting multi shooter per target at Canberra regularly.As time goes by, we will get an idea as to how often colisions occur. Today we may have been lucky. It is, after all, a purely random event.

Geoff.