Cartridge with the highest velocity

thebigslide said:
So this is something that is possibly feasible, but once combustion begins - anything loose is all pretty homogenized in there due to turbulance. Another issue that comes up when using loose powder is that the ignition source is at the base. It's less than ideal since the pressure wave is actually forcing the charge up towards the bore. You really don't want to toss a slow burning powder up into a large cavity and expose it to an ignition source.
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Pressure waves are highly undesirable inside gun chambers. They can cause big problems (including blowing up a gun) so usually a lot of effort is put into controlling or reducing the amplitude of any pressure waves. To intentionally use pressure waves inside a gun chamber would be a highly unconventional and/or experimental approach.

Also, I think your burn rate factor chart is upside down! Compare the grain size of H4198 with H335 for example and you will see that the H335 has more surface area per grain and a smaller grain size, yet has a much slower "burn rate" due to it's chemistry.
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It wasn't a ranking of relative importance, it was a listing of what the various factors are.

Looking at a ball powder such as H335 or WC748 is quite informative. Their grain size is *much* smaller than stick powders of similar burn rate (e.g. 4895). Also, the grain geometry of a spherical powder is "regressive" (as the powder grain burns, less surface area is exposed), whereas the geometry of a cylindrical stick with a central hole is "neutral", or if there is deterrent on the outer surface but not the inner surface it is "progressive".

In propellent burn rate calculations I have seen, combustion temperature is usually something that can be masked by wrapping it up in enthalpy along with pressure since the heat loss due to soak is an unknown. A large, conservative error factor is prudently included. Firearms propellents may be a little different here. Programs such as quickload naively ignore this.
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I am not understanding how you are connecting enthalpy with propellant burn rates, nor with heat loss to the barrel.

This is something I don't have a lot of experience with. Can you recommend any papers on the subject? I am curious about the chemistry of typical deterrents and I really have little background in the design of typical modern deterrents and would like to know more.
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No particular papers come to mind but if you keep an eye out for "propellant geometry", and "regressive" or "neutral" or "progressive" burn characteristics you will definitely see the connections.

There is a good book called "Interior Ballistics of Guns" (or perhaps "Internal Ballistics of Guns"?) that was written in the 50s or so that is pretty much the classic text on this. I would think a good university engineering library ought to have a copy. I'm not sure if it is written by "Corning", or if there is another good ballistics book by Corning.
 
Wow! Thats a lot of technical info to digest. I'll have to re-read that a few times.
Thankyou both for posting.

Something else that I recall reading was about the shape of each grain of powder. For a solid shape, either round or extruded, as it burns from the outside to the centre, it gets smaller, and therefore less surface area. So it produces less gas as it burns.
In comparison, the very large "grains" of powder used in a battleship gun (about the size of a mans thumb) have holes running the length of the kernel. As the kernel burns, it burns through the tunnels also. This causes the tunnels to grow larger as the powder is consumed, and so generates MORE gas as it is consumed. Clever!
 
tootall said:
Wow! Thats a lot of technical info to digest. I'll have to re-read that a few times.
Thankyou both for posting.

Something else that I recall reading was about the shape of each grain of powder. For a solid shape, either round or extruded, as it burns from the outside to the centre, it gets smaller, and therefore less surface area. So it produces less gas as it burns.
In comparison, the very large "grains" of powder used in a battleship gun (about the size of a mans thumb) have holes running the length of the kernel. As the kernel burns, it burns through the tunnels also. This causes the tunnels to grow larger as the powder is consumed, and so generates MORE gas as it is consumed. Clever!
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Ok, so who is going to be the first to bore out kernels of Varget?:D
 
tootall said:
Something else that I recall reading was about the shape of each grain of powder. For a solid shape, either round or extruded, as it burns from the outside to the centre, it gets smaller, and therefore less surface area. So it produces less gas as it burns.
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Yes. That's called a "regressive grain", meaning that exposed surface are decreases as the powder kernel burns.

(Extruded (stick) powders without a central hole are called "cylindrical" geometry.)

In comparison, the very large "grains" of powder used in a battleship gun (about the size of a mans thumb) have holes running the length of the kernel. As the kernel burns, it burns through the tunnels also. This causes the tunnels to grow larger as the powder is consumed, and so generates MORE gas as it is consumed. Clever!
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Artillery stick powder is made with a single perforation (like a macaroni), or with multiple perforations (seven is common; one in the middle and six surrounding that one).

single-perf powder burns from the outer surface and also the inner surface (unless the outer surface is prevented or delayed from burning, by applying a "deterrent" coating). As the outer surface burns in, its surface area decreases (so that part is "regressive"). As the inner surface burns out, its surface area increases (so that part is "progressive"). Interestingly these effects cancel each other out, so a simple single-perf powder grain is said to be a "neutral grain" (it exposed surface area is constant).

A seven-perf powder stick is a bit more complicated. In the initial part of its burn, the seven interior holes are strongly progressive. But when they burn through to connect each other (so there are six "slivers" plus the outer shell), the burn rate becomes regressive.

Budweiser360 said:
Ok, so who is going to be the first to bore out kernels of Varget?:D
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Most smallarms stick powders already have a small hole running through them. I can't recall if Varget does or not (and am too lazy to go to my gunroom and check!). Most of the IMR powders do (though it can be difficult to see because the graphite coating on IMR sticks mostly obscures this; you have to be determined to find it in order to see it!).
 
rnbra-shooter said:
There is a good book called "Interior Ballistics of Guns" (or perhaps "Internal Ballistics of Guns"?) that was written in the 50s or so that is pretty much the classic text on this. I would think a good university engineering library ought to have a copy. I'm not sure if it is written by "Corning", or if there is another good ballistics book by Corning.
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Theory of the interior ballistics of guns, by John Corner (I just Googled it);)

http://www.google.ca/webhp?client=f...=f&aqi=&aql=&oq=&gs_rfai=&fp=7262352ca2544df8
(I hope that crazy long link works...)
I sniffed around for a free .pdf copy, but most sites want you to register with a credit card first. I'll find one eventually.
 
rnbra-shooter said:
Pressure waves are highly undesirable inside gun chambers. They can cause big problems (including blowing up a gun) so usually a lot of effort is put into controlling or reducing the amplitude of any pressure waves. To intentionally use pressure waves inside a gun chamber would be a highly unconventional and/or experimental approach.
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That's kind of what I'm talking about doing by including a secondary propellent - just in a controlled manner. There will always be one pressure wave. I'm just talking about adding a second, longer, lower peak - in a controlled manner. The whole thread is pretty unconventional - in a very interesting way. Don't see too many of these.

rnbra-shooter said:
There is a good book called "Interior Ballistics of Guns" (or perhaps "Internal Ballistics of Guns"?) that was written in the 50s or so that is pretty much the classic text on this. I would think a good university engineering library ought to have a copy. I'm not sure if it is written by "Corning", or if there is another good ballistics book by Corning.
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Right on! I think I cited that book once, so I know there's a copy at the U of M. Wishing I'd read it through at the time. Thanks to Tootall for the link.
 
I read a magazine article probably 10 years ago about a new .30 cal cartridge that had a "ignition tube" that basically lit the powder directly behind the bullet, thereby greatly increasing velocity because the pressure pushed only the bullet down the barrel, not powder and bullet. By burning the powder inside the case, the mass of the "projectile" ( bullet and powder) was decreased. IIRC they were getting 3200 fps with a 240 gr bullet. I haven't heard or read anything about it since. The concept sounded good to me, but I know squat about internal ballistics.
 
tootall that is the book I was referring to.

thebigslide said:
That's kind of what I'm talking about doing by including a secondary propellent - just in a controlled manner. There will always be one pressure wave. I'm just talking about adding a second, longer, lower peak - in a controlled manner. The whole thread is pretty unconventional - in a very interesting way. Don't see too many of these.
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"pressure wave" is usually taken to mean a nonuniform pressure distribution in the chamber. In conventional charge design this should be as weak as possible (i.e. ideally there should be not be a travelling pressure wave; at higher charge:shot mass ratios, there will be a pressure gradient from the breech to the base of the bullet)

There is a nonconventional design idea called a "travelling charge effect" you might be interested in looking up. I am not aware of it being successfully implemented.


tnegrin83 said:
I read a magazine article probably 10 years ago about a new .30 cal cartridge that had a "ignition tube" that basically lit the powder directly behind the bullet, thereby greatly increasing velocity because the pressure pushed only the bullet down the barrel, not powder and bullet. By burning the powder inside the case, the mass of the "projectile" ( bullet and powder) was decreased. IIRC they were getting 3200 fps with a 240 gr bullet. I haven't heard or read anything about it since. The concept sounded good to me, but I know squat about internal ballistics.
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Was it done some time ago by a wildcatter named Rocky Gibbs?

As far as I understand the results of the "front ignition" concept, it did NOT produce useful improvements (it is essentially the reverse of the "travelling charge effect" concept).
 
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So which CGN'er is going to be the first to build a privately owned light gas gun? 20,000 FPS could be fun!

I'm thinking a .50 BMG cartridge firing a HDPE (plastic) piston/bullet, an old beer can for a burst disk and we weld a .17 HMR barrel on the front of the thing to fire the projectile. Hydrogen is as simple as a car battery and some water.

How hard could it really be? ;)

:D:D:D
 
rnbra-shooter said:
Was it done some time ago by a wildcatter named Rocky Gibbs?

As far as I understand the results of the "front ignition" concept, it did produce useful improvements (it is essentially the reverse of the "travelling charge effect" concept).
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I don't recall the designer of the cartridge. I think it was in a Guns & Weapons for LE magazine. I'll try my google-fu, and see if I can find anything.
 
rnbra-shooter said:
Damn typo, I missed a very important word in the following:
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When I read your first response I found myself wondering, HOW??? It didn't make much sense unless I was missing something fundamental.

That certainly clears it up, and gives me a little more confidence that my ideas of the workings of internal ballistics are still on track. :D
 
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