doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Damascus explained

Raimey - There are three distinct sets of gas involved in a gun discharge. So far, I have been speaking of the gas evolving from the powder burn. It is hot enough that the speed of sound in it will be higher than we normally associate with gun discharge velocities. The second gas set is the air in the barrel in front of the wad. It will be compressed by the discharge, but much will flow out of the barrel prior to the shot exceeding its sonic velocity. The third set is the air outside the barrel. It will have typical sonic velocity.

The shot in the barrel will acclelrate to some velocity based on pressure of the powder gas on the wad base, friction of the wad/shot to barrel, and back pressure of the air in front of the wad. The powder gas can't flow at supersonic speed without passing through a nozzle, but doesn't need to as it can flow fast enough at subsonic (for it) speeds to achieve the needed shot velocities. The air in front of the shot is simply pushed out and we know that its compressive pressure is less than the pressure of the powder gas as shot loads continue to accelerate in long barrels. As the shot load exits into the ambient air, it may well be above the sonic speed of that air. Remember, sonic speed depends on temperature of the gas (air). As the shot charge exits the muzzle, a sonic shock wave will form on the bow of the charge and will trail away from it until the charge drops below sonic velocity. Muzzle velocities for shotguns typically range from 900 fps (slow) to 1500 fps (very fast). Typical sonic velocity of ambient air at the earth's surface is around 1100 fps.

How fast? Well, as I recall the limit for powder gas in a barrel is around 10,000 fps. If you need to go faster, you need a rocket or a rail gun.

Again, if that is not clear, ask questions - I should be able to explain this.

Excellent description. You must be a Rocket Scientist as I had many post grad classes with folk destined to work in that area for MICOM(ARDEC(?)) on Redstone Arsenal. So what is the peak temperature in the barrels & is it a linear or non-linear relation to the sonic velocity? Last, typically, where will the shotcharge experience the highest velocity(1/2 way down the tube, 3/4s the way, just outside the tube)?

Kind Regards,

Raimey
rse

The peak temperature will be within the shotshell hull and will occur during the time of peak pressure. The pressure will peak within the first couple of inches of shot travel; usually early within this period. Shot acceleration is directly tied to pressure, so the peak acceleration will be very early in the shot travel. Peak velocity, however, will occur at the muzzle as the shot continues to accelerate all the way down the barrel; at least for useful barrel lengths. The acceleration is down to around 20-40 additional fps in the last few inches. If you were to make a long enough barrel, the friction forces and air back pressure would eventually equal the force of the powder gs pressure and the shot would stop accelerating; longer and the shot would actually slow down.

Speed of sound in a gas is typically related to the square root of the temperature; higher temperature equal higher speed of sound. So, it is non-linear.

So, the first derivative of velocity has a practical application almost everywhere even, in the realm of hunting/shooting. Back to a Damascus type question: will the effect of the shotstring/wad reaching the sonic velocity at the muzzle have any different effect on Damascus versus fluid steel, for useful barrel lengths? Thanks for your time, Rocketman.

Kind Regards,

Raimey
rse

"So, the first derivative of velocity has a practical application almost everywhere even, in the realm of hunting/shooting." Yes, indeed and boy howdy it does!

The first appearance of a sonic shock wave is outside the muzzle, so there is no influence on the barrel, whether steel or damascus. Good question, IMO. Questions?

Rocketman:

Excellent, excellent exchange of information of my rambling questions and your precise, descriptive answers. I was deeply curious as I am trying to develop a particle model of the shotstring exiting the tubes. Currently, Roster seems to be a hot topic, but I had quizzed him and he inferred that it would be quite difficult. Many Thanks.

Kind Regards,

Raimey
rse

Thank you for the kind words. Glad to share any info in my posession.

While I agree with Roster that your model would be difficult, let me add a bit of fuel to the fire. IMO, shot acts as a fluid in the choke constriction. That is, it is experiencing internal pressure due to the powder gas pressure behind it and the pressure of the air being forced out of the barrel. The shot can't support shear forces, but is confined by the barrel. As it exits the muzzle, the shot pieces "push off" of each other as the relieve the pressure they are under. Some of the "push-off" is in a sideways direction and causes pellets to depart with a small sideways velocity, along with their axiel velocity. This sideways velocity is what we see as dispersion. Further, the air trapped within the shot column is pressurized and expands as soon as the shot clear the barrel. Some of the expansion creates a "sideways" wind that also imparts some sideways velocity to the shot pieces.

Now, the good part. When a fluid flows through a constriction, such as a choke cone, the velocity must increase to maintain mass flow rate. The increase in velocity comes at the expense of pressure; the pressure drops. The drop in pressure reduces the pellet to pellet push-off and the "sideways" wind. Therefore, dispersion is reduced. We know that the velocity of the shot charge is incresed by about 1 fps per 0.001 of constriction. So, the increase in velocity is confirmed.

That could be helpful in your model.

Once again, great info. That confirms what I had in mind. The front little speed demons who take the brunt of the cone are pushed to the wayside to the outer portion of the pattern in the fringe area and begin to lag behind with a slower individual velocity. And what you've described would account for the change in the traverse direction as opposed to the longitudinal. I haven't replicated Mr. Brister’s experiment just yet. Fluids, thermo, etc. will yield a very complex model. The only thing missing is plasma.

Kind Regards,

Raimey
rse

I contacted the German Gun Collector's and inquired for any information they may have gathered for German sources of damascus or any Germanic centers that may have produced them.
They very kindly responded, with correspondence from Axel Eichendorff responding to Dietrich Apel.

In part, here is the response:


Once again the name of Manfred Saches surfaces.
So we have some dates with some more possible lines of research that will need to be followed...

Here is the book mentioned: Die Jagd-feuergewehre: Anleitung zur näheren Kenntniss U. Zum richtigen By Adolf Zimmer

Pete

Found another neat on-line book with a perspective other than Greener's

Shooting Simplified By James Dalziel Dougall 1865
http://books.google.com/books?id=BkACAAAAQAAJ&dq=w+greener+barrel+patents

A variety of iron termed “silver steel” is preferable to all others.
(Unfortunately there is no description of the production process)

It will at once be seen that the necessary time taken by three workmen in this cold-hammering process very much enhances the value of fine barrels. It is in this part of the process that the continental workmen are deficient…We have great faith in English pluck and muscle. No foreigner strikes a blow upon the anvil like your English workmen…

p. 18 There are various kinds of flaws in barrels, such as “cracks”, “sand holes”, and what are technically termed “grays.” They are those little specks in the iron…from rust showing more upon them than upon the smoother surface.
(What follows is a discussion of the various barrel flaws)