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Post by Deleted on Mar 5, 2011 10:09:17 GMT -5
To the pt guys,
What would the optimum or most desirable pressure trace be ?
I understand that you guys are testing for safe pressures ,but I get lost on the what kind of curve your all are looking for. Also, the secondary spike is just mindboggling who would have thought that phenomenon was occuring. Keep up the pressure tracing,
I think it is real ground breaking stuff and I'll keep trying to figure out what the heck ya'll are talking about.
Thanks,
Greenhorn
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Post by ET on Mar 5, 2011 15:42:34 GMT -5
Greenhorn
The fundamental principle of a pressure trace is showing the amount of pressure in a bore at a specific time during its cycle through the bore.
What is considered an optimum trace is showing peak pressure within set limits with some pressure still present when the bullet leaves the bore and no presence of a secondary pressure spike.
Bullet time in the bore is usually under .0015 seconds so this time frame from 0 to .0015 seconds (1.5 milli or micro seconds expressed on the trace) is normally our point of interest.
3-main factors that influence the pressure trace outline are, amount of powder and burn rate of powder, projectile weight and bore resistance of projectile to on-coming pressure.
Once the basic concept is understood then one can observe what affect the 3-main factor variables have on the pressure trace outline. This is where it gets a little more complicated in deciphering what a trace outline displays. The 3-main factors are sort of intertwined producing an end result of a trace. If they aren’t matched up so to speak than a less than ideal or desired trace is produced.
Hope I have clearly expressed this enough and not created more confusion.
Ed
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Post by Jon on Mar 5, 2011 20:00:05 GMT -5
Et. Very well put. I don't think the problem is in the trace but the fact that is loaded from the muzzle and does not have the same amount of resistance as a c/f. Welcome to a new world Just differant extreems.
Jon
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Post by ET on Mar 5, 2011 21:00:41 GMT -5
Jon
Yes shooting a muzzle loader and CF rifles presents two different conditions (bore resistance) affecting the pressure cycle in the bore. The catch is finding the right load combination to restore the balance to what is seen as a good resulting pressure cycle in the bore. And that can be a challenge for the shooter to find for a desired velocity.
Ed
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Post by Jon on Mar 6, 2011 7:57:38 GMT -5
ET +1
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Post by spoonover on Mar 6, 2011 9:13:21 GMT -5
Seating bullet, what happens to pressures if projectile is not sitting on the powder?
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Post by ET on Mar 6, 2011 17:15:06 GMT -5
Seating bullet, what happens to pressures if projectile is not sitting on the powder? Spoonover Good question but with so many variables in play I couldn’t provide any kind of answer with any certainty. Ed |
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Post by Jon on Mar 6, 2011 19:24:22 GMT -5
You may want to talk to Tom Post at swing lock? His guns have a chamber and as I understand He shoots less than a full chamber.
Jon
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Post by Deleted on Mar 7, 2011 12:44:52 GMT -5
Thanks ET for clearing a fews things up for me. I am visualizing "I think" how a duplex works. The starter ignites, pressure builds, bullet unseats and starts accelerating down the barrel meanwhile the second powder ignites and builds pressure behind the bullet to keep the acceleration up. If the second powder burns to quickly then thats when you get a second pressure spike.
Thats how I am percieving whats happening. Am I at least on the right track???
Greenhorn
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Post by ET on Mar 7, 2011 15:14:07 GMT -5
Thanks ET for clearing a fews things up for me. I am visualizing "I think" how a duplex works. The starter ignites, pressure builds, bullet unseats and starts accelerating down the barrel meanwhile the second powder ignites and builds pressure behind the bullet to keep the acceleration up. If the second powder burns to quickly then thats when you get a second pressure spike. Thats how I am percieving whats happening. Am I at least on the right track??? Greenhorn Greenhorn It is easier to visualize looking at one powder (the main charge). What is important is that the burn rate maintains enough pressure to keep up with the bullet travel as it moves down the bore. If the bullet manages to race ahead of the burn rate the decline pressure will drop faster than desired/needed for the remaining unburned powder. Powder is not burning fast enough. Here a catch up burn occurs rebuilding pressure again with the unburned powder producing the secondary spike. I know the next question would be why so fast a pressure rebuild and how could it exceed primary pressure peak in some cases with the bullet already moving? I have an idea (theory) why this is occurring but no proof to back it for now so I don’t plan to present it just yet. Ed |
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Post by Deleted on Mar 8, 2011 8:36:48 GMT -5
I am just going to keep reading and taking all this in. There is so many things going on in just a few milliseconds. I am interested and am going to look into the different characteristics of the many available powders.
Could there be a concentrated "load" of unburned powder behind the moving bullet and when it ignites under pressure it spikes the pressure up again? Thanks again ET and you all for
your input.
Greenhorn
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Post by edge on Mar 8, 2011 8:53:43 GMT -5
While we think of Duplex as layered I don't think that they really shoot that way. IMO, the primer ignites a cone of powder that burns up then sideways depending on how far the bullet moves.
RB and Toby played with "reverse duplex" and I am not so sure that would not be the better route. There have been many attempts over the years to get the primer to ignite the powder directly behind the bullet instead of at the base of the cartridge.
edge.
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Post by ET on Mar 8, 2011 9:17:56 GMT -5
Greenhorn
Hope you don’t think I’m coming down on your line of thought and pushing my concept of what’s happening.
I don’t see powder concentration causing the pressure spike but the lack there of. If the powder remains concentrated (packed together) then the flame has limited access to the amount of powder it can ignite at a given point in time. Now if the powder column looses concentration say breaks apart this would allow the flame access to burn more powder at a given time generating more and faster pressure buildup would be the result.
This is my perception of what may well be occurring.
Wasn’t ready to present this possibility just yet but guess I’m now exposed. ;D
Ed
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Post by moto357 on Mar 8, 2011 16:28:29 GMT -5
curious about a couple of things as i read this.. one is the theory of unburnt powder finally going off creating the second spike we are seeing. if this is the case, even when using a single where the second spike is seen, would't the velocity be noticiably lower than a similar charge in a cartridge? i would think a consistant "push" behind the bullet versus one push then nothing for 1/3 or more of the barrel would result in a noticible decrease in fps??
next is my idea of the duplex.. nothing more than my thoughts, but i would think as pressure builds that alone would have the "main" charge lit as well.. not like its going to wait to start its burn? i think the fact that we see this secondary spike with both singles and duplexes leads maybe to like ET was saying about initial pressure which is lacking without the case or engraving effect we see in cartridge guns. just my thoughts on this
love all the new stuff we're learning here!
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Post by ET on Mar 8, 2011 17:35:22 GMT -5
Moto357
I enjoy others looking at this condition and sharing their thoughts.
So far I have yet to see on a trace where the transition burn occurs between duplex loads.
For the secondary spike to occur a source for additional pressure has to exist and at the moment can only see unburned powder as the source.
Not sure if this is a good example but will present it anyway.
Think of one car pushing another. The pushing car will get the front car up to speed by maintaining a contact force. Now both cars are moving but if the driving contact force is reduced too fast by the car pushing then separation occurs.
Now some might see that with a faster burning powder this may have a faster pressure decline on a trace and they are basically right. But if there is no unburned powder left to burn then no secondary spike can be generated.
Hope I haven’t added any confusion here sharing my thought process because it may seem a little cluttered at times. ;D
Ed
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Post by Deleted on Mar 8, 2011 18:48:26 GMT -5
ET,
I see what your saying I was kinda right I just shouldn't have used "concentrated" the unburned pattern of powder going down the barrel under pressure but instead of packed together all the unburned powder is clompletely exposed to the flame and discharges again spiking pressure. IMO your dead on.
Thanks again guys,
Greenhorn
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Post by ET on Mar 8, 2011 19:41:24 GMT -5
ET, I see what your saying I was kinda right I just shouldn't have used "concentrated" the unburned pattern of powder going down the barrel under pressure but instead of packed together all the unburned powder is clompletely exposed to the flame and discharges again spiking pressure. IMO your dead on. Thanks again guys, Greenhorn Now we are on the same wavelength as this is what I visualize is happening also with slower powders causing that secondary spike affect. Ed |
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Post by ET on Mar 9, 2011 6:04:15 GMT -5
While we think of Duplex as layered I don't think that they really shoot that way. IMO, the primer ignites a cone of powder that burns up then sideways depending on how far the bullet moves. RB and Toby played with "reverse duplex" and I am not so sure that would not be the better route. There have been many attempts over the years to get the primer to ignite the powder directly behind the bullet instead of at the base of the cartridge. edge. Edge In the first part I know what you are expressing but can’t agree on that one. I see the powder as a solid before the burn and pressure rise from the start of a burn would tend to act on the solid body of unburned powder by pushing it forward making it a progressive burn. Of course this is with a proper filled column of powder to begin with. On the reverse duplex part I can agree there may be a benefit here not discovered yet. But the ratio of powders may have to be really altered or even the difference of burn rate characteristics may need to be broadened for the desired affect of shifting the pressure decline of the faster powder towards the muzzle. As for the third part of igniting the powder on the top instead of the bottom of the powder column all I can say is that it’s the first time I’m hearing about that one. So no comment here. Ed |
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Post by Deleted on Mar 9, 2011 9:10:47 GMT -5
ET,
Knight came up with a power stem breechplug in their .54 cal ml.
I ran across their design and asked on the board what people thought, ROSSMAN "Encyclopedia" brought out that the reverse burn concept has been around for awhile, he found a photo of a cartridge design that had the primer under the projectile, the photo was taken about 50 years ago or earlier.
Anyway, I will bring my design up to you, lets say your load fills
2 inches in the barrel. If you have a power stem that potrudes 1.85 inches above the face of your breechplug then you have a reverse burn.
I realize you would have to have a different or maybe adjustable length stem for different loads ,but I was just extrapolating what knight had come up with.
The feedback I got was that the stem would get carbon fouling and not much more was posted.
I think a duplexs or even Richards triplex loads would benefit
from this design.
I don't know how to post links on here yet,but checkout knights powerstem bp and you will see what I am trying to say.
Let me know what you think !!!
Thanks,
Greenhorn
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Post by edge on Mar 9, 2011 9:29:40 GMT -5
ET, the powder is protected from the primer flame because it is shielded by the BP. The only area that gets flame is directly above the flash hole ( VL ), and the rest is shrouded.
IMO, you will have a geyser shaped ignition moving forward much faster than toward the side of the bore or sidewalls of a cartridge. If the flash hole were the size of the bore then I would agree that it would probably move forward more as a continuous cylinder.
As far as the forward ignition, there are some cartridges where they install a tube from the primer up to the front of the cartridge. The theory is the the powder would burn back toward the breech as the bullet went the opposite direction. Supposedly less wear on the throat since the burning powder is not impinging on it.
edge.
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Post by Savage Shooter on Mar 9, 2011 9:31:16 GMT -5
IMO there is a lot more "reverse" burn than we think about. We normally just think that we are igniting powder from the rear and nothing could be farther from what is actually happening during ignition.
Especially with the hot primers we are using to insure dependable ignition.
The primer is "shooting" a very hot gas jet that not only ignites the rear of the powder column but also "injects" hot gas "fire" that penetrates up into the powder column, (how much or how far into I have no idea).
Aint seen it tho so some is just speculation and reasoning.
This has to make the powder column burn from the inside out also. I think Edge's description of the ignition sequence is pretty much right on.
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Post by ET on Mar 9, 2011 12:07:31 GMT -5
Edge
No disagreement as to the source and location of the ignition. Yes a cone burn affect would be started. As to final shape I don’t know.
But a geyser penetration by a flame would go against the burn rate property of the powder.
How can the center of the powder column have a faster burn rate than say the sides?
When the flame hits the powder and begins a point of powder burning that burning has to expand in all directions in a consistent manner dictated by the powder burn rate.
Trying to figure out exactly what is happening gets interesting through discussions and different viewpoints.
Thanks for the heads up on the other approach to powder ignition. It may be old to some but new to me.
Savage Shooter
No disagreement about a primer introducing a hot jet of flame to the powder but when the powder is compiled and compacted like a wall penetrating that wall can’t be so easy. I would think it has to burn into it and if burning is initiated then the rule of powder burn should take over.
Greenhorn
Thanks
I vaguely remember someone mentioning the approach of using a stem with multiple holes and thought this was his original idea. Must of missed Rossman’s follow up post.
Ed
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Post by edge on Mar 9, 2011 13:11:52 GMT -5
Perhaps a geyser was a bit misleading, but a primer will ignite powder a significant distance from the VL hole. How far I will leave to your imagination  Now the powder all has the same burn rate and the powder next to the BP and the bore walls are over 0.200 from the vent hole! A small load of duplex probably only takes up a 1/4 inch at the base of the load. Clearly you would be into the main load long before all of the primary powder were ignited. IMO, for anything else to happen would necessitate the powder to burn faster sideways than forward. edge. |
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Post by ET on Mar 9, 2011 14:11:51 GMT -5
Edge
No response coming and you know why.
Ed
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Post by edge on Mar 9, 2011 14:20:47 GMT -5
Somewhere on the net I bet there is a finite element analysis of a cartridge going off. I have searched but can't find one......maybe someday edge. |
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Post by spoonover on Mar 9, 2011 19:28:29 GMT -5
Is there a point all powder will burn with out a flame?
Just pure friction alone from molecules colliding and creating heat. Primers do throw flame, and that is not enough to combust powder at times. When a tight seal is not made or a bullet is not seated down to the powder the pressure is not there to cause the diesel effect (for lack of better term)?
Powder column will burn as long as there is pressure on all sides and burn not only from the bottom but all that is being affected by molecules colliding? Please correct me if I am on the wrong tract!
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Post by ET on Mar 9, 2011 21:33:31 GMT -5
Spoonover
By flame are you referring to the primer or the powder burning?
Yes conditions of containment and resistance to expanding pressure are needed to assist the burn as it perpetuates.
The load can be seated slightly off the powder and the primer flame can still ignite the powder giving the start of the burn support until pressure begins to develop for the burn to carry itself.
I honestly don’t know what role friction plays as I see expanding heat from the resulting burn from powder grains as the carrier of the burn to other nearby grains of powder.
Ed
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Post by spoonover on Mar 10, 2011 0:35:44 GMT -5
Spoonover By flame are you referring to the primer or the powder burning? Yes conditions of containment and resistance to expanding pressure are needed to assist the burn as it perpetuates. The load can be seated slightly off the powder and the primer flame can still ignite the powder giving the start of the burn support until pressure begins to develop for the burn to carry itself. I honestly don’t know what role friction plays as I see expanding heat from the resulting burn from powder grains as the carrier of the burn to other nearby grains of powder. Ed Primer flame, and with the pressure it creates. Take away pressure, the flame from the primer will not always burn the powder, IMR4227 needs more than flame to ignite, confine space for a reliable burn? This is my theory, if I am wrong disregard. |
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Post by ET on Mar 10, 2011 6:31:30 GMT -5
Spoonover
Basically speaking, yes.
This definition for burn rate sums up the factors that affect the combustion of a smokeless powder.
Burning Rate - An arbitrary index of the quickness that burning propellant changes into gas. Burning rate is controlled by the chemical composition, the size and shape of the propellant grains, coatings and the pressure at which the burning takes place.
Ed
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