Fluid Dynamics...

[Tigger]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

[mistermack]

The spring example was mine, just a fanciful mind-picture.
But to clarify, I wasn't talking about a sound wave travelling through the metal, I meant a compression/expansion wave in the springs.
I don't think the speed of that would be anything like the speed of sound in metal. Not in the springs that I've handled, anyway.
.

A sound wave is a compression expansion wave. That's exactly what they're defined as. The speed of your compression/expansion wave is going to stall out at 'sound.'

Note that that would be the upper limit that the compression/expansion wave propagates. Since it has to do work on the object to move it, it has a different energy balance than a sound wave. For the fluid version, that's wind.

Yes, a sound wave is a compression wave. But the speed of sound in metal would be very much higher than the speed of a compression/expansion waves along a typical spring.
What I was trying to get at was that if you had one single spring pushing a bullet along a gun barrel, you have a limited top speed.
If you had a dozen, you could achieve a much bigger top speed than a single spring could achieve, as the springs nearest the bullet are being physically accelerated, as well as releasing their own energy.
If you imagine a gas as a series of springs, you get a similar picture.

[Blondie]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

It's a field known as "Ballistics". I guess you've never heard of it, but it is very math heavy. Tell me the projectile weight, the charge weight, type, the form factor of the projectile (or the ballistic coefficient), and the length of the barrel and I'll tell you the muzzle velocity or its velocity at 300m. Hell I'll even tell you how much kinetic energy it has at both and how much it will drop from 0 at 300m.

[Tigger]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

It's a field known as "Ballistics". I guess you've never heard of it, but it is very math heavy. Tell me the projectile weight, the charge weight, type, the form factor of the projectile (or the ballistic coefficient), and the length of the barrel and I'll tell you the muzzle velocity or its velocity at 300m. Hell I'll even tell you how much kinetic energy it has at both and how much it will drop from 0 at 300m.

I have a degree in maths and stats so Your maths knowledge impresses me not.

[Blondie]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

It's a field known as "Ballistics". I guess you've never heard of it, but it is very math heavy. Tell me the projectile weight, the charge weight, type, the form factor of the projectile (or the ballistic coefficient), and the length of the barrel and I'll tell you the muzzle velocity or its velocity at 300m. Hell I'll even tell you how much kinetic energy it has at both and how much it will drop from 0 at 300m.

I have a degree in maths and stats so Your maths knowledge impresses me not.

Then your ignorance of ballistic formulae is particularly shameful.

[Tigger]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

It's a field known as "Ballistics". I guess you've never heard of it, but it is very math heavy. Tell me the projectile weight, the charge weight, type, the form factor of the projectile (or the ballistic coefficient), and the length of the barrel and I'll tell you the muzzle velocity or its velocity at 300m. Hell I'll even tell you how much kinetic energy it has at both and how much it will drop from 0 at 300m.

I have a degree in maths and stats so Your maths knowledge impresses me not.

Then your ignorance of ballistic formulae is particularly shameful.

Not at all: my knowledge of a friend's interest is quite apposite.

[Mousy]

Then your ignorance of ballistic formulae is particularly shameful.

Your knowledge of jest is shameful.

[Coito ergo sum]

gas pressure has a speed of sound?

Well I think I'm about to learn something new ... *clicks on link*

Yes, since sound travels faster or slower depending on density.

[GreyICE]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

It's a field known as "Ballistics". I guess you've never heard of it, but it is very math heavy. Tell me the projectile weight, the charge weight, type, the form factor of the projectile (or the ballistic coefficient), and the length of the barrel and I'll tell you the muzzle velocity or its velocity at 300m. Hell I'll even tell you how much kinetic energy it has at both and how much it will drop from 0 at 300m.

Ah. Will your calculations use tables derived from basic physical principles, or experimentally produced tables?

Yeah, that's what I thought.

[Blondie]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

It's a field known as "Ballistics". I guess you've never heard of it, but it is very math heavy. Tell me the projectile weight, the charge weight, type, the form factor of the projectile (or the ballistic coefficient), and the length of the barrel and I'll tell you the muzzle velocity or its velocity at 300m. Hell I'll even tell you how much kinetic energy it has at both and how much it will drop from 0 at 300m.

Ah. Will your calculations use tables derived from basic physical principles, or experimentally produced tables?

Yeah, that's what I thought.

If I was to use experimentally based tables, such as those available from ammunition manufacturers, I would have to ask for the specific ammunition make, caliber, and type wouldn't I?

You assume too much me thinks.

[JacksSmirkingRevenge]

This thread is pretty lol. All Bri wants to know, I suspect, is how fast his projectile is going to be moving when it leaves the barrel.

Impossible to calculate directly. I suggest using a strobe light and a shutter-free camera.

Not even literally that: just "how fast?" in terms of "will it smash that window 300 metres away?"

Actually, I can calculate all of that and design an airgun to suit whatever requirements using the Gas Gun Design Tool. I've used it in the past and other people using it have compared it's predictions against chronographs etc. very favourably.
http://www.thehalls-in-bfe.com/GGDT/

All I really wanted to know was how can a pre-charged airgun push a pellet faster than the SOS in air?*

You can guestimate the speed of a projectile by firing it at a target over a measured distance and recording the muzzle sound and projectile impact on a laptop using Audacity or something. The sound wave recording can then be compared to a time line and the appropriate calculations done.






* - Actually, the thought occurs that one could use a less dense "gas spring" such as helium. ...That might work.

[Blondie]

Or you could just wire up a circuit timer that activates when the trigger is pulled and deactivates when the target is struck - simple enough to do.

However, the speed of the projectile is not a constant, as I'm sure you're aware. You'd simply find the average velocity for that range.

[mistermack]

I still don't think the SOS is the limit.
The SOS is the speed at which a wave travels, RELATIVE TO THE MEDIUM.
At the point where the pellet reaches the end of the barrel, the fluid is travelling at the same speed as the slug. You would have to add that speed to the SOS of the air in the barrel, to get the theoretical limit.

[JacksSmirkingRevenge]

Or you could just wire up a circuit timer that activates when the trigger is pulled and deactivates when the target is struck - simple enough to do.

However, the speed of the projectile is not a constant, as I'm sure you're aware. You'd simply find the average velocity for that range.

I think this is the easiest answer, when I can afford one:-
http://cgi.ebay.co.uk/SHOOTING-CHRONY-F ... 588826734b

[GreyICE]

If I was to use experimentally based tables, such as those available from ammunition manufacturers, I would have to ask for the specific ammunition make, caliber, and type wouldn't I?

You assume too much me thinks.

Oh no, I know exactly how hard combustion is to model, and exactly how unlikely it is that you have a computer simulation of the various variables set to run at a moment's notice.

Your tables are experimentally derived.

@Biri, if the question is just how your air gun can fire faster than the speed of sound, there is two ways. First, use a nozzle/diffuser. That's reasonably impractical for a fireable air gun (it'll be very long, most likely). The second way is just to get a very light gas. Light gasses have higher speeds of sound at STP (because speed of sound is based on molecular velocity, and low mass molecules and atoms have high velocities at the same energy) so will fire the bullet faster than the speed of sound in atmosphere.