At what distance does a handgun round hit max velocity?

[Mal H]

It occurs to me that some physicists believed that a bullet is of cylindrical, full wadcutter shape or at best a round ball. Whatcha think?

I can't, my brain hurts.

I have to admit, you lost me there, Pistolsmith. I don't see how any of the 3 paragraphs address the question asked. (BTW, Galileo used metal balls of different weights, not a feather and a rock. And his physical experiment may be myth, he presented it in a thought problem only, no evidence that he actually carried it out.)

 

[Pistolsmith]

I'm no Galileo, but I did the above experiment with the stated conclusions to prove what I'm saying about bullets being aerodynamic. Elmer said it in 1929; I'm just repeating what HE (not Galileo) said. Besides, I don't think the Eyties let Galileo own a gun, since the Pope made a very long and thorough investigation, then condemned him for his "damnable heresy". ...And him being infallible in all matters of faith and morals...oh, sorry he didn't declare himself infallible for a number of years yet..
I didn't do it at the Pisa tower, but the UPS tower looked right for the experiment, so I let 'er rip. Reporter for the school paper thought it was relevant, and it made page 1. Physics prof just groaned and rolled his eyes upward.
You sound like you never had any fun as a kid!
Did I ever tell you about the Physics instructor who was caught by a campus cop in the back seat of a Studebaker parked on the quad at 2 in the morning with one of his female students? Oh, sorry, that's totally irrelavant, like all of my other posts.

 

[Mal H]

You sound like you never had any fun as a kid!

Not sure how you came to that particular conclusion, but you're pretty much 180 degrees out of phase. If you only knew ...

 

[griz]

I suppose it accelerates for a short while the gas is still pushing it, but it is a VERY short distance. When the base of a 9 mm bullet is about0.09 inches away from the barrel, the open area where the gas can escape is already equal to the area of the base of the bullet. We are talking small fractions of an inch, then the bullet starts slowing down.

It comes down to physics. I had a friend tell me that a baseball continues to accelerates for about a hundred feet after it leaves the bat. He couldn't name the force that did it, but he was sure because it looked like it had to in order to rise so fast. He was wrong. I'm not sure he thought the rules of physics applied in all cases.

 

[WESHOOT2]

SO I'M SITTIN' HERE

Looking at the March '95 Shooting Times article of high-speed photography capturing the firing of a Ruger P90.

I think it's over at the muzzle, me.

 

[Bill Adair]

I suspect a bullet, which is accelerating down the bore under intense pressure, continues to accelerate for a very short distance after exiting the muzzle. Not because the gasses are still pushing after it leaves the barrel, but because of the inertia of an accelerating mass.

The principle is simple physics. Items accelerating will continue to accelerate, until resistance overcomes inertia. If the bullet is still accelerating when it exits the muzzle, it will continue to accelerate for fractions of a second, until air resistance overcomes that acceleration, and velocity begins to decline.

We already know that barrel length effects muzzle velocity, and that in most cases a longer barrel will produce higher velocity, so we are pretty sure that the bullet is still accelerating, at least from most handgun, and short rifle barrels.

Measuring this would be very difficult (not impossible), with modern sensors. Getting someone to fund such testing might well be impossible!

I don't believe that gasses exiting the muzzle accelerate the bullet at all. The sudden drop in pressure when those gasses vent is almost instantaneous, thus the propelling force is lost.

There is also severe turbulence on the bullet as the gasses vent around it, which might possibly contribute to aerodynamic resistance, and reduce the velocity.

Bill

 

[Tim Burke]

The principle is simple physics.

Apparently not.
From a Jr High School science project, Newtons 1st law is: An object in motion tends to stay in motion, and an object at rest tends to stay at rest, unless the object is acted upon by an outside force.
It doesn't say an object accelerating will tend to accelerate.
The 2nd law is force = mass times accelleration.This can be expressed as F=ma, F/m=a or F/a=m. It is clear that if a mass is accelerating there is a force acting on it.

 

[Pistolsmith]

Think this one over: As the bullet exits the barrel, friction from the rifling is being reduced. From the exact time the parallel portion of the bullet begins to exit until the base has left the bore, there will be a miniscule INCREASE in velocity, since pressure remains behind it and friction is decreasing.
Perhaps a 9X23 Win caliber bullet would gain a bit from gas impinging at 45,000 psi, for a distanced measured in thousandths of an inch, but I'd seriously doubt that a .380 would be so increased.
As stated far above, the only PROVEN (i.e. DOCUMENTED) increase came from a Lewis gun firing .30-06 ammo.
You having fun yet?

 

[pogo2]

Sure the bullet accelerates after it leaves the barrel.

It accelerates toward the center of the earth due to the effect of the gravitational force on it.

Now in the direction of its travel, the bullet decelerates due to the force of air friction.

Think vectors.

 

[Pistolsmith]

And the rate of deceleration is directly proportional to bullet shape.
Also, a cloud of gas may well escape the muzzle BEFORE the bullet begins to protrude. (See Naramore's book "Principles and Practice of Reloading Ammunition" for a high speed photo of a Tommy gun barrel with the cloud of gas escaping as the bullet just begins to emerge from t he bore.)

 

[Dave R]

I believe that the RATE of acceleration changes as soon as the bullet leaves the barrel, but the bullet may continue to acclerate after it leaves the barrel, whether or not gas is pushing it.

Think about this. When you floor your car, and it is accelerating smartly, then you lift at peak acceleration...the _speed_ of the car will continue to increase for a short time, even thought the _rate_ of accleration drops as soon as you lift.

I think the same with bullets. If the bullet is still accelerating as it leaves the muzzle, it will continue to increase in speed for a short distance, even though the rate of acceleration begins dropping immediately.

 

[WESHOOT2]

I HAVE BEEN THINKING (WAY) TOO MUCH ABOUT THIS

:banghead: :banghead: :banghead:

Dave R,

mebbe..............

 

[Pistolsmith]

No offense, but your car continues to accellerate because you have gotten behind the power curve. Gasoline left in the carbuerator or in the injectors will continue to flow after release of th accellerator, albeit for a very short period of time, before it begins to slow down. When that happens on a 747, you belong to the ages.
Weshoot2: I'm not through with you yet. Look for my new post titled "More Ballistic Trivia." As the old sarge used to roar: "I didn't say you're dismissed...."

 

[MrAcheson]

Alrighty time for the engineer to speak up.

A few issues here. An supersonic bullet like a 9mm is travelling faster than the speed of sound (obviously). Pressure waves only propogate at the speed on sound unless something is pushing on them to go faster like the combustion of a propellant.

So the bullet leaves the muzzle. Its supersonic. The pressure wave pushing it is also supersonic because it is fueled by combustion and is constrained by the barrel. However once you leave the barrel it is no longer constrained (so the shape of the pressure curve changes) and the remaining powder burns up incredibly fast. So you have a very very short distance before the bullet is outrunning the driving pressure curve. So once the bullet is a fraction of an inch past the muzzle, it is going as fast as it ever will. Technically that is not the muzzle velocity but its so close it doesn't really matter.

As for the car and continue accelerating argument, no. Objects move at constant velocity (zero is a constant velocity) unless accelerated by a force. Your car keeps going faster because the engine hasn't stopped pushing the car yet.

 

[Blackhawk]

MrAcheson, you're a spoilsport. This could have gone on for many more pages and made my face hurt from smiling.

 

[Mal H]

Me too, BH. I gave up several posts ago and just sat back smiling.

 

[Pistolsmith]

Mal:
Well, somebody hadda be there, or it would be a Physical THEORY and not a PHYSICAL LAW.
My regret is that you and I can't go back in time to watch Galileo drop his balls off the top of the tower of Pizza...(Does that sound right?) to see if they strike the ground at the same time. Only, we'd have to remember to take our Streamlites...it DID happen during the Dark Ages....

 

[Dave R]

It all depends on whether the bullet is still accelerating when leaves the muzzle. If the barrel is too long, and the propellant has burned and the bullet is decellerating, then of course it won't accelerate when it leaves the muzzle.

However......

If the bullet is accelerating when it leaves the muzzle (which I believe is the case in most pistols), it will continue to accelerate for some short time after it leaves the muzzle, as I said earlier. Here's why.

First, you need to differentiate between acceleration and speed. Just to use round numbers, lets assume the bullet is accelerating at the rate of 100fps per millisecond as it approches the muzzle. That is, every millisecond the bullet is going 100fps faster than the previous millisecond. At 8 ms its going 800fps, at 10ms its going 1000fps, etc. So that rate of 100fps per millisecond is the rate of acceleration.

Once it clears the muzzle, the rate of accelleration slows. So it goes from accelerating at 100fps per ms, to accelerating at 50 fps per millisecond, to accelerating at 25 fps per millisecond, to 0fps per millisecond. But it is still picking up speed during that process, even after it leaves the muzzle.

Then after it hits accleration of 0 fps per ms, it goes to -10 fps per millisecond, -25fps per ms, -100fps, etc. At that point it is losing speed.

So I don't know how far after the muzzle its rate of acceleration hits 0fps and it begins to slow, but it is still picking up speed after the muzzle, during that time that the rate of acceleration goes from 100fps per ms to 0 fps per ms.

Someone with better math skills than me can figure the distance out.

 

[MrAcheson]

Sorry Dave R but acceleration does not have to be continuous on the macro scale. If you want to be technical all forces are distributed in time and space so yes, acceleration must be continuous, but it is continuous on a time scale which is so small it doesn't matter. You are incapable of noticing it without multi-million dollar equipment. We are potentially talking about nano or picoseconds here.

Velocity does have to be continuous on the macro scale. According to newton's laws if no force is acting on an object, the object does not accelerate. Period. If a bullet accelerates any after it leaves the gun it means that a force, like residual pressure from the barrel, is accelerating it. Otherwise it is slowing down due to air resistance. This is fundamental physics.

 

[Dave R]

You convinced me, MrArcheson.

If the scenario I described were accurate--if you fire the bullet in space, where no no ther forces act on it after it leaves the muzzle, then the bullet would accelerate continuously. Nope.

Soon as it leaves the barrel, that's as fast as its gonna go. 'Cept maybe if the gas column pushes it a bit more after it clears the barrel.

Shoulda known that a real engineer would know more than a guy who once got an A in Physics 101.

 

[Mal H]

What MrAcheson said.

Dave your error is all contained in the one sentence: "Once it clears the muzzle, the rate of acceleration slows." As MrA said, acceleration can stop instantanously. There is no physical law that states that the rate must slow down, unlike velocity (when the body in motion is acted upon by a force vector in the opposite direction of its travel).

[Edit]
Nevermind. We were posting at the same time. I see you've figured out the error of your ways.

 

[ryucasta]

The attached file shows the calculated external ballistics for a 9x19 cartridge that’s configured for USPSA/IPSC Open Major.

 

[Mal H]

While interesting, that quicktarget chart doesn't help. The first increment is at 5 yds which is well beyond the fraction of an inch to a few inches where there might be some additional acceleration of the bullet.

 

[ryucasta]

Mal,

There are a lot of factors involved for example was a fast burning or slow burning powder used? What was the ambient temperature, atmospheric pressure, length of barrel, projectile material, powder charge, coating if any etc? Way too many variables anyway this thread reminds me of a debate that I read about from the middle ages where scholars debated how many angels could dance on the head of a pin.

 

[Mal H]

You're certainly right about that!! Oh, and the answer is infinity.