Is this too much science?!


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mugsie
April 6, 2010, 08:09 AM
These are the things which go through my head - I was thinking about powders - how do they measure burn rate? Is there a formula or procedure they use?

So where is this going? Well, I was thinking, in order to get the most efficiency out of a rifle, and possibly to achieve the most optimal speed for a given barrel length, wouldn't one want a powder which completely burns out at exactly the same moment the bullet leaves the barrel? More powder creates greater pressure which would allow the bullet to exit faster, but then there would be a lot of unburned powder. Faster bullet - more wasted powder. If the powder burned out at the bullet exit time, the speed and powder efficiency would be optimal. Yes?

Now that I'm thinking about it, how does one measure the time it takes from primer strike to the time the bullet exits the barrel? Factors such as crimp or neck tension, barrel length, burn rate, primer power, bullet friction, etc all need to be taken into consideration. How is this measured? Is there really any science to any of this, or do we simple cram a bullet into a case full of powder and measure it's performance through the use of chronographs and accuracy? I'm beginning to think that it's all witch craft anyway!

Your thoughts? (try not to think too hard about the infinate possibilities or you too will be up all night discussing various combinations and scenarios with yourself!)

:evil:

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Owen
April 6, 2010, 08:42 AM
power and efficiency don't go hand in hand...

cisco11
April 6, 2010, 08:53 AM
Power and efficiency DO go hand n hand. Take a look at Hornady Superformance ammo.
Cisco

helg
April 6, 2010, 09:07 AM
The measuring procedure is named "closed-bomb test", where pressure vs time is measured. Results of the test are calculated to "vivacity" curve, which describe full progress of the burning. The curve definitely gives more information than just a burning rate. The rate, however gives ballpark evaluation of the powder.

Unfortunately, I can not find an easy Wiki link on this. The powder burning model details are well described in QuickLoad manual.

RidgwayCO
April 6, 2010, 09:30 AM
Mugsie, you sound like someone who would really like the software program QuickLOAD.

http://www.neconos.com/details3.htm

243winxb
April 6, 2010, 09:38 AM
http://www.fbi.gov/hq/lab/fsc/backissu/april2002/mccord.htm#table1 Some info on powders. Google this >army research laboratory closed bomb facility measurement of propellant burning rate

Jon_Snow
April 6, 2010, 11:24 AM
Try this: http://www.amazon.com/gp/product/1420066188/ref=oss_product

I'm still working my way through it, but it's a great resource if you have an engineering/physics background. The long and short of it though is that the burn rate is not constant, it is a function of the material and also the temperature and pressure. That's how smokeless powder works. As it burns it produces a lot of gas in a small space, raising the pressure and causing it to burn faster. That's why powder laying on the ground just kind of burns and fizzles without a big boom.

mugsie
April 6, 2010, 11:35 AM
So Quickload explains things like this? It gives me the ability to experiment on paper, things like various bullets, different powders, different barrel lengths, pressure curves, accuracy etc? It may be something I'd be interested in.

For instance, all things being equal, every rifle should shoot in exactly the same spot for each variation of bullet and powder. Bullet X, powder Y, harmonic resonance should always be the same, so POI is Z. Diff bullet, diff powder, diff POI but always the same for that particular bullet and powder combo. Yet it isn't! Aughhhh - I want it to be. Things like this constantly fill my head.

Remember - don't do all the things the little voices tell you to.....

918v
April 6, 2010, 11:51 AM
Yes, QL does all of that and ten times more.

Zak Smith
April 6, 2010, 12:26 PM
QuickLoad is invaluable, but it does have its limitations.

cheygriz
April 6, 2010, 12:34 PM
Maybe it's time to stop agonizing over minutiae, trying to overanalyze every detail, and just enjoy the hobby! :p

helg
April 6, 2010, 12:52 PM
All but harmonic resonance is covered by the QL. QL calculates only what happens inside the bore. Powder/bullet/seating/barrel length, bore tension. The resonance depends on some parameters, which are located outside the bore. QL, however, gives you travel time for bullet in the barrel, and knowing the "sweet spot" travel time for one powder/bullet/seating, which gives the best accuracy, should easily predict what is going to be the most accurate load for other powder or bullet.

RidgwayCO
April 6, 2010, 02:48 PM
helg is technically correct, in that QuickLOAD is an internal ballistics program ("what happens inside the bore"). But QuickLOAD also comes with QuickTARGET, a very nice external ballistics program that predicts what your bullet will do after exiting the bore.

TexasShooter59
April 6, 2010, 07:19 PM
You want some science? You really do?

Go right here (http://www.amazon.com/Rifle-Accuracy-Facts-Harold-Vaughn/dp/1931220077/ref=sr_1_1?ie=UTF8&s=books&qid=1270595805&sr=1-1)!

When I read this, it was like reading an engineering textbook from multiple disciplines.

Ol` Joe
April 6, 2010, 09:55 PM
QL builds a computer model of what a combination of components should produce but it is just a model. There is a bit of tolerance in all powder, primers, rifle throats, bore geometry, and other things that will affect the out come. It can be surprisingly accurate and a fantastic tool but, still one should start with the suggested beginning loads and work up.

helg
April 6, 2010, 10:05 PM
Ol` Joe

What is, by your experience, FPS difference between Quickload calculations and actual chronograph measurements?

ranger335v
April 7, 2010, 08:48 PM
"QL builds a computer model of what a combination of components should produce but it is just a model."

Yep, computer models are just models. To get real data still requires field testing.

IF your bore and chamber and case internal volume and primer lot and power lot closely match the models the programmers used you may get a very accurate computer geek prediction. But that's a lot of "ifs". Meaning, it's less a science than it is computer gaming for folks who enjoy gaming for its own sake. IMHO, of course.

helg
April 7, 2010, 09:26 PM
In my experience, if I measure everything accurately, QL-calculated muzzle speed stands within spread of the data that are measured by a chronograph. This is not counting revolvers though, where the measured speed is always less than calculated one - for known reason.

Case volume, bullet weight and other rifle/cartridge parameters are measured - by user - and supplied to the QL program. This data, especially, case volume, show tangible effect to the calculated results. Powder lot-to-lot variations, in my experience, do not affect the results anyway beyond measured ES variations. I do not shoot 50 years old powder though. I heard that authors of the QL program refuse to include some powders (TrailBoss is one example) because of the inconsistency.

jeepmor
April 7, 2010, 10:05 PM
You want science. You buy the strain gage setup that mounts on the outside of your barrel which you can then connect to a laptop. You then shoot a known pressure load and you have a calibration. You can then measure your pressure curves directly and figure it all out with data, real data, not some compilation of data, but real, hands on, empirical data.

Right where the rubber hits the road, not the the electron through the transistor....oops, you'd be using a laptop, scratch that.

I saw a link here on THR once, but I'm not ambitious enough to go find it for you. However, such a system does exist and this is how manufacturers now do it on test barrels and what not over the old copper slug method of CUP units.

There is no such thing as too much science, but there is such a thing as enough information to make a practical decision. In most cases, this is the debate between the mathematician and the physicist. You clearly want to be a physicist here.

Owen
April 7, 2010, 10:17 PM
no, this is the debate between the engineer and the physicist.

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