Checking your own projectile BC

[Woody_rod]

Can't say much about them...they still under development. I have some coming in 185 grain for 30 cal and 168 in 7mm. There are others as well, but they are the ones I am interested in for now for F/TR and F Open.

[smc977]

and performance, this can be used as a benchmark for the new projectiles.

What I have been trying to figure out, is how to measure the TOF at 1000y for a true reading and cross reference to the known ballistics performance. I do realise that the atmospheric conditions should also be known, but if the known projectile is tested and recorded on the same day, then this can be the comparative data on which to base an educated guess of the BC. A percentage of difference is what the outcome will be.

Ok, so here is my idea to measure the TOF:

I downloaded an audio app for my laptop called "Audacity" which is free and works on my system as is. This program can record sound at decent quality and can also show it on a time graph.

Add two x handheld CB radios as commonly used at rifle ranges for the "microphone" at the 1000y end, and get set up at the range - one radio goes next to the laptop as the receiver, the other goes onto the target. I am thinking of taping it to the bottom of the frame with the mic pointed towards the target face (upwards).

The target puller / marker can then operate the target radio by taping the button down for a send signal, so the sound of the projectile going past will be sent back to the receiver and laptop mic to be recorded.

The laptop is situated next to the shooter on the mound and readied. The shot is fired - the sound will be clearly recorded at mound end, with the supersonic crack heard over the radio from the target, sent back to the firing point.

Some time loss will be evident (speed of sound across the distance to the microphone at the target end and the shooter end), BUT, if the same setup is used for all testing, including that for the known projectile, then the real data collected will still be useful.

Some very small time loss will be for the 1000y and radio comms, but this is so small as to be of no importance.

I hope to trial this shortly to test the custom projectiles I was talking about previously.[/quote]

try filming the shot and use a steel target like they do on youtube and then you can run the clock on the recording. A lot easier to set up and a bit more accurate. need a good quality camera but not to expensive.

[DannyS]

Don't believe everything you see on youtube

[AlanF]

Okay, we've seen several possible ways of measuring BC, and all have some merit, but with all due respect, none would stand up to scientific scrutiny. e.g. all rely on chronographed velocities (how can you be sure about them!) and/or G7/G1 drag tables. And what if different bores affect bullet jackets differently, and hence BC? etc. etc.

As F-Class shooters, why are we concerned about BC? I would suggest the main reason is to be able to compare the wind deflection of different projectiles. Can I also suggest that if we're prepared to devise an elaborate test to do this, then why not go straight to the crux of the matter, and directly compare wind deflections between different loads. It shouldn't be much harder to do than some of the above, and has the advantage of directly measuring what we are interested in knowing i.e. is load A better in the wind than load B?

Here's my initial thoughts on the method :

Wait for calm conditions (late afternoon at my range), and shoot both loads alternately at long range until satisfied they have identical zeros, or the difference in zero is known.

Put the rifle away, ensuring the scope is undisturbed.

Wait for steady cross-wind conditions, than shoot the same two loads alternately at the same long range for say 5 shots each. Average the deflection distances for each load.

Then you will be able to say something like "load A has 7% less wind deflection than load B". By the way, if a load has 7% less deflection in say a 10mph wind, then theoretically it will have the same 7% advantage at other wind speeds.

Alan

[Woody_rod]

Alan, please explain the difference between BC and wind deflection?

[AlanF]

Alan, please explain the difference between BC and wind deflection?

Rod,

Not sure why you're asking, but basically, BC is a way of describing bullet drag with a single figure, and wind deflection is one of several observable effects of bullet drag (drag can be described simply as air resistance).

Alan

[DannyS]

Answer to all your problems found go to http://www.accurateshooter.com/featured ... ndia-labs/

[Barry Davies]

BC is dependent upon ( among other things ) Temperature, Barometric pressure, altitude and humidity. all which have as many combinations as lotto.
So what's really the point as you spend most of your day calculating instead of shooting.
Barry

[Gadget]

Boy's Boy's Boy's
Been there, doing that, it work's.
OZ Score rule's

Graham

[Norm]

Hijacked by pointless ELR noise.....

Don't know why you would say that? Someone tries to help you and you seem to take offence. Why ask the question if you don't want an open discussion on the technical side of the problem. ELR was raised as it is where the differences between projectiles are more obvious in a lot of long range bullets. Out to 1000 yards a lot of .308 bullets are in a similar velocity range and exhibit the same differences as the long range projectiles are at ELR.
Just have a look at how many people have trouble in F-Standard with short barrelled .308's past 800 yards.
There are ways to work this information out in a practical manner but maybe you are not interested.

Alan,
I think your method is quite practical and so long as you get the wind conditions you want it would give you a direct wind drift comparison which is all you really need for F class target shooting. It is a very different situation to what is needed for long range field shooting.

[Woody_rod]

Hijacked by pointless ELR noise.....

Don't know why you would say that? Someone tries to help you and you seem to take offence. Why ask the question if you don't want an open discussion on the technical side of the problem.

I started the thread, others starting talking about something unrelated - called hijacking. IDGAF about ELR, only 1000y as it applies to my role in the AU F Class team - hence this thread.

Start a thread on ELR somewhere else if you want to discuss it further.

[Woody_rod]

BC is dependent upon ( among other things ) Temperature, Barometric pressure, altitude and humidity. all which have as many combinations as lotto.
So what's really the point as you spend most of your day calculating instead of shooting.
Barry

Winning is the point. The people we are competing against spend all day calculating, we need to as well.

All of the items you provided are constants for different projectiles, fired at the same time, therefore it makes no difference to the outcome.

The BC is not known on the projectiles I have, I want to test them to work it out. This thread started with my concept of how to work it out via TOF.

[Woody_rod]

It is a very different situation to what is needed for long range field shooting.

No it isn't any different. Physics are what they are - no matter what the rifle or projectile, they all follow the same rules.

[DannyS]

Ooh, we are a bit touchy Woody.

[Woody_rod]

Ooh, we are a bit touchy Woody.

Not really, just get sick of the BS people post on here.