We shot a gun horizontally and we want to know: 1. Where does the bullet reaches its highest speed? (not accounting for gravitation) 2. Where does its acceleration ends? My guess is that it depends on the length of the barrel. But speaking of short barrel handguns, I am guessing a few inches after the bullet leaves the barrel. Why? The force propelling it forward is the exploding gas behind it. The force slowing it down is air resistence and the barrel's sliding resistence (or whatever you call it). Once it reaches the end of the barrel the gas suddenly has all dirrections to expand thus the thrusting power suddenly disappears. But for a few inches I would say it still has effect and force on the bullet. Now it is possible that in long barrel shotguns the gas expanded in the barrel so much that its pushing force is much less at the end of the barrel. But looking at shots we usually can see a decent muzzle flash showing that plenty of force still left in the gas even when the bullet is already in the air. Also the airresistance is much less then the barrel's sliding resistance, so when the bullet is out in the air, suddenly there is less resistance trying to slow it down. Any thoughts??
Acceleration stops pretty much at the end of the barrel, but muzzle flash makes this hard to measure precisely. I think any acceleration after that point is pretty negligible compared to in barrel acceleration. So highest velocity is also as the bullet exits the barrel too.
What about the resistance difference between the barrel and just thin air? Suddenly the barrel isn't slowing down the bullet...
It's always less by the time the projectile reaches the end of the barrel. Apart from, say, ETC weapons* and a few extremely carefully designed (and expensive) experimental ones maximum pressure occurs about 1/3 - 1/2 of the way down the barrel. Please Register or Log in to view the hidden image! Above is a typical pressure curve (this one for 7.62mm ammo - weapon not specified). As with most pressure curves I've seen it never actually drops to zero, but doesn't record any values after the end of the barrel. As I said in my post in the other thread, because of the extremely sharp fall in resistance (i.e. the switch to air resistance only as opposed to barrel friction and air resistance) and the fact that there is still pressure behind the bullet there will be some acceleration, but only a very small increment. Note also the velocity curve on the graph - it's still rising, but starting to flatten out. * ETC weapons are designed to give lower peak pressures but sustain the peak for longer, thus giving a higher muzzle velocity for a lighter barrel.
OK, but how long was the barrel? If it was 17 inches than I am right with the "a few inches after the barrel" idea. Also what about the bullet storing a little kinetic energy when it slightly shrinks (I assume) from the force pushing it throught the barrel? (spring effect) Once it is free it regains it shape and gains a little speed from that... Check this video of the muzzle flash of the handgun, it is pretty damn long, like 2 feet, I would say, I am guessing plenty of force left to still move the bullet forward while it is already in the air... http://www.youtube.com/watch?v=_Rtw91crys8&NR=1&feature=fvwp This is a long barrel gun and still plenty of gaspower left after the bullet left the barrel, in Ultraslo: http://www.youtube.com/watch?v=M2b4AK19gVw&feature=fvw Now it is possible that the bullet has already reached its highest acceleration in the barrel, but maybe not its speed....Although it is also possible that the bullet is going much faster than the gas behind it, thbus there is no extra speed gain from the gas....
I've never ever seen a pressure curve that continues for longer than the barrel - IOW the travel recorded will be only the barrel length. 21 inches is the length of barrel of, for example, the FN SLR, 22.2 inches for the MG3... etc. No, although a bullet is larger than the (nominal) calibre it gets the rifling forced into its body by the lands (that's what gives the striations so beloved of shows like CSI). It doesn't "spring back" particularly. Please Register or Log in to view the hidden image! And even if it did any KE from "springing back" would mostly be radial - at right angles to the line of flight.
So if, for some reason, we want high velocity impacts, we could make two stage ammo. The gun - even a handgun - could fire a length of barrel with a bullet in it. The barrel would go off near the target - we can brainstorm how this is determined later when applying for a patent.
Well that's kind of the idea behind high explosive rounds, shells, grenades, whatever; lob something near the enemy which then blasts high velocity shrapnel all over the place. Just not quite as directional as lobbing a barrel at someone Please Register or Log in to view the hidden image!.
We can achieve ~2km/ sec now. What do you call "high-velocity"? Some anti-tank missiles have a two-stage warhead, heck, some have a multi-stage warhead. Er, firing a secondary barrel would increase the throw-weight: which means there would be a reduced initial velocity (or a concomitant increase in recoil), and what stops the second barrel (which is not supported) from using part of the charge to recoil, thus wasting energy and not giving that much extra velocity to the projectile?
Anything I can't see. I suppose I was really thinking of a combination low and high velocity. I know we have rifles - and even handguns - that fire incredibly far, so the bullets must start out very fast. I have no idea if my little playful suggestion has any use, but your responses here made me think of a two stage bullet for handguns. Yes, I was thinking small scale. yes, even I with my limited engineering capablities know this. I wasn't clear. It was the idea of having slow - relatively - then fast. Of course this issue is also present in staged rockets and missiles. As the previous poster points out we have weapons that function loosely like this - grenades. I wonder if it might somehow be useful to have a silent weapon, perhaps even with a mechanical firing process - it ejects the bullet/barrel toward the target and the barrel fires the bullet at close range. One advantage would be the sound would arise at the victim, perhaps covering the location of the shooter. Of course silencers do this to some degree. Could even be a crossbow that fired the barrel. Hey, I am just brainstorming. Just thought there might be some use to a slow then suddenly up close fast bullet. Perhaps it would work well against certain kinds of body armour, since you could have your highest velocity at target.
Ah, then you want (will a dozen be enough to be going on with ma'am? Please Register or Log in to view the hidden image!) self-forging fragments, also called explosively-formed projectiles. Reliant on the Misznay–Schardin Effect these are small squat cylinders contained in an artillery shell - which then drop out, look for a target and, finding one, go off, not only spitting out a "bullet" at high velocity but also manufacturing that bullet from a disc of heavy metal.
Thank you. I also found this, the Gyrojet gun, which fires small rockets... http://en.wikipedia.org/wiki/Gyrojet Still neither is quite what I meant. I like the idea of a barrel flying toward the target and then the bullet is fired from this barrel. May be a useless idea - or perhaps somehow useful in some other field like mining or dentistry - sometimes i scare myself - but it became stuck in my mind. What can I do?
Doreen, there was this guy, Sir Isaac Newton. Got read some of his thoughts, then you'll only be about 300 years behind current understanding of physics. Oh, and hopefully understand why the above idea of yours just won't work.
Yes, the abandoned gyrojet concept. Why was it abandoned? Because it was shit. In a fire fight, there are a few things you want to happen. You want the round you discharge to hit your target, and stop it. The gyrojet could not guarantee either of those. It was inaccurate because of the engineering tolerances balancing the thrust. It was crap at close range because the round accelerated in flight, and had no short range stopping power. Simply, a round accelerated in a conventional barrel has predictable muzzle energy, and a predictable trajectory. Gyrojet rounds were less predictable, ie, aiming wasn't good, as the round itself moved after discharge.
Bang. Well I've forgotten more than I can remember, but it depends on a fair bit. A pistol bullet will end acceleration about at the outside end of the barrel. I doubt the flash/jet effect will be anywere near the confined pressure when in the barrel. Point is it doesn't matter compared to the short barrel length. And the barrel length in a pistol isn't as critical as one might imagine as a fast burning powder is used. With a .22 rimfire, after about 16 inches or so the bullet starts slowing up. With centerfires, pressure and velosity can very a lot. Again all increase in Vel. ends with the barrel end for all practical purposes. Again, no one cares too much as all velosity is measured well away from the muzzle blast, something like 10 or 12 feet. A big banger, like the magnums, a 30+ inch barrel may give more velosity, but becomes very unwieldy and not worth the gain. Shotgun barrels are similar to the centerfires, I forget the best length but would guess about 26 to 28 inches. The longer barrels used (regardless of what some owners believe) are only useful for pointing ability and maybe balance. Like pistols a fast burning powder is used. Thoughts aplenty. . . Facts, maybe. :shrug: But yes, at the end of the barrel it's all over.
Depends who you're talking about. http://www.ojp.usdoj.gov/nij/training/firearms-training/module07/fir_m07_t07.htm http://www.wikipatents.com/US-Patent-4030097/muzzle-velocity-chronograph/Page-1 Please Register or Log in to view the hidden image! And guess what that "cage" is on the end of the barrel. A muzzle-velocity monitor. Considerably closer than 10 or twelve feet.
Oooh, cute. I have a little chrono that straps to the barrel of airguns, to measure muzzle velocity, that uses a couple of infra red LEDs. I guess that gizmo must use something else, as IR would get interfered with by the muzzle flash.
If I remember correctly, it's a "simple" capacitance device, which checks for passage of an object going through the holes in each of the triangular (?) plates. Since they are a known distance apart then all you need is the time between first and second plates for the on-board ballistic computer to calculate the V[sub]0[/sub]. It's a more-or-less standard fitting on high rate of fire anti-aircraft guns, so that the computer can correct for variations in muzzle velocity due to barrel wear: the rate of fire will wear the gun bore out, causing a gradual decrease in muzzle velocity with successive shots. If the V[sub]0[/sub] is monitored then the computer can correct the aim point as required.
