[/ QUOTE ]I've thought a lot on how I could create a two chamber powder plug so after you reach peak pressure and pressure starts to drop - you would melt thru a barrier to the 2nd powder chamber - the 2nd powder chamber would have a much higher burn rate. All this to flatten the pressure curve and thus produce maximum velocity at safe pressure.
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Been thinking the same thing. All you need is an auxillary chamber say on the bottom of the bbl, a flash hole and a check valve.
As the bullet passes the flash hole the powder in the aux chamber is ignited and the check valve closes off the rear portion of the barrel. Lota details to work out but who knows, stranger things have been accomplished.
Hope the above is taken for the humor thatis intended. [img]/ubbthreads/images/graemlins/grin.gif[/img]
Keep the discussion going, I really do appreciate the great cross section of talent/education etc. that is on this board.
The whole discussion will go away when projectiles are accelerated via electricity. [img]/ubbthreads/images/graemlins/frown.gif[/img]
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!
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<font color="purple"> You are correct Jon A. I work in science and occasionally search the literature for references and patents in these areas. There are some fairly sophisticated internal ballistics codes that have come out. They do not rely on the ideal gas law. Even low pressure Helium doesn't strictly obey the ideal gas law. Accurate modelling of any REAL gas is much more complicated. You should load your cartridge with Magnesium-Teflon-Viton (MTV) and then see if you believe in hotter powders!</font>
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Great. Provide a citation or explanation for what creates pressure in burning powder besides heat. I've already shown the other alternative n is insignificant.
You are correct in that gases deviate from the IGL - but it is a good approximation and as the chemists have stated -[*]powders are primarily differentiated by burn rate - not reactants.[*]Different powders deviate from the IGL in a very consistent fashion
For all the naysayers of the simple heat pump approximation - please provide an explanation rather than a summary dismissal.
Even some reproducible data with a thermocouple and chrono (controlling for ambient temp.) would be helpful. But simply saying I shot my gun with H-50BMG powder a few weeks ago then wc872 yesterday and the barrel was hotter with H-50BMG shows nothing. How much hotter? What was the shot rate? Ambient temp? Unless you control and measure these factors you only have the impetus to do so, but cannot come to any conclusion.
There are other factors which can explain throat erosion. How abrasive are the powders? Some powders are far more abrasive than others. This is especially important before the bullet forms a gas seal.
This does give me a good idea. Perhaps I can video my 50 BMGs at night (which have a jynormous flame) and see if I can figure out how much unburnt powder remains when the bullet exits.
The reason I'm so familar with bullet acceleration being so well approximated by PV=nRT is my extensive discussions with some chemists in my quest for a multi-stage powder that can flatten the pressure curve. I'm not the first to think of this idea.
You say that I am summarily dismissing your points. I am not, but I think that you are dismissing mine. I can find some references at work tomorrow. For that matter who are the chemists who told you that burning powder produces no gaseous products? I'm a chemist myself. I don't know everything about propellant chemistry, but I know that powders have a wide range of formulations. They can be single-base, double-base, or triple base. They include different amounts of plasticizers, burn rate modifiers and possibly coolants. So I would say that the chemistry of different powders burning could be quite different. It doesn't take the conditions of a detonating high explosive to deviate from the ideal gas law. All real gasses deviate.
I'm trying to think about your points. Maybe you can clarify what (in your mind) is happening during combustion?
If only heat is being produced, then how? Don't you think that chemical change and creation of reaction products is producing the heat?
I found one reference for you already:
MODEL FOR COMBUSTION OF TRIPLE-BASE PROPELLANT WITH
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<font color="purple"> b1g b0re I don't intend upon debating powder burn rates and mathmatical equations but here are some facts.
#1 Yes H-50 BMG is listed as slower than H-870.
#2 WC872 is stated as being able to use H-870 data and AA8700 but My top end load for H-50 BMG was 100 grains behind either a 168 SMK or a 169.5 wildcat and on hot days ( above 85 ) will show pessure ( developed that load during the cold months ). So far I'm up to 102 grains of WC872 with the same bullets and have reached the <u> <font color="red"> </font> same velocity </u> <font color="blue"> </font> as H-50 BMG but have not gotten any pressure signs what so ever! I intend upon going up with the powder once again to wherever I get the best results or pressure signs. This tells me it burns slower than H-870, AA8700, and H-50 BMG powder since I have exceeded the previous load data for each powder by 2 full grains already.
#3 Kirby and jwp 475 also found the WC872 to be a slower burning powder in their tests by exceeding H-870 load data by a good margin along with H-50 BMG data as well.
#4 As far as barrel heat I have not used any hi tech device to measure it but when you can feel a difference by grabbing the barrel after 3 shots of the same bullets only different powder then there must be a difference. True I have not reached max level of WC872 yet and when I do there may be no noticable barrel heat difference at all and when I get there I will say I found no noticable difference in barrel heat at max loads for each powder. Right now it's a night and day difference between the 2 after 3 shots The BMG I assure you that you will turn it loose shortly after grabbing it and the WC872 you can hold with no pain or teeth gritting for as long as you want.
Like I said I don't want to argue mathmatics because I hated frieking equations and formula's in school and I don't like them any better now.
I'm only stating facts that I have so far and when I get more data collected on this subject I will share it over on a thread of mine in equipment reviews titled Wildcat bullets consistency and accuracy.
I'm through hijacking Kirby's wonderful thread about his new Allen Mag.
Sorry for the Hijack Kirby, Len, Dave, Ian ! [img]/ubbthreads/images/graemlins/frown.gif[/img] </font>
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Double ditto on the Hijack apologies.
You guys are doing the important work - what powder (and load) produces the best results. I was only listing published burn rates - I'm not sure they are accurate. I plan on getting an 7mm Allen uber mag some day. I'm Kirby's biggest fan.
Burn rate is dynamic and dependent on many factors, temp and pressure being significant. Perhaps if you compared the H-50BMG and WC872 pressure curves you would see the H-50BMG spiking to max pressure then dropping off quickly (less area under the curve) - so less terminal velocity from the H-50BMG. Because H-50BMG (guessing here) drops off so quickly, when the bullet exits, there is still plenty of powder left burning to heat your barrel. If my conjecture is true, your barrel will last longer with WC872 while producing higher velocities.
Without temp, vel and pressure curve data, it's all conjecture. What is fact and not conjecture is that WC872 produces superior results - and that's really what we are all after.
I've ordered several batches of WC872 so I can get similar good results in some of my rifles.
And for the zillionth time: <ul type="square">[*]I agree, no gas exactly follows the IGL - but for simple heat pumps (like guns) it is an excellent model[*]If the well understood and accepted heat pump mechanism is not the primary accelerator of bullets, provide credible evidence/explanation of an alternative mechanism such that two appropriate powders can produce the same terminal velocity with different heat flux. By appropriate I mean not using a powder that burns so slow much of the powder burning occurs after bullet exit and simply contributes to kick and heating the barrel.[/list]
2nd Summary: <ul type="square">[*]Kirby makes the hottest/flattest shooting wildcats[*]Kirby's uber mags like WC872[*]The only thing that matters is the measured performance (velocity/accuracy) of these guns. (And RUMS, I have 4 RUMS [img]/ubbthreads/images/graemlins/smile.gif[/img] )[/list]