Bullets accelerate after they leave the barrel???

[old Grump]

Comments by Bruce Jones

1) Winchester introduced the .308 commercially in 1952. The US Military didn't agree to adopt it as the basic cartridge until 1954 and no weapons were chambered for the government in it until 1957. Thus military followed commercial production.


Back (http://www.angelfire.com/art/enchanter/pigboard.html#b1)

2) The US Army tested over a million rounds of all makes and manufacture and that is the test result. It has been duplicated by the FBI as well.


Back (http://www.angelfire.com/art/enchanter/pigboard.html#b2)

3) This 200gr .38 Spl reproduced the ballistics of the British 38/200, so had a muzzle velocity of 630fps. There is a 200gr .357 at 950fps that is even more effective.


Back (http://www.angelfire.com/art/enchanter/pigboard.html#b3)

4) I was a bit skeptical about the 230gr FMJ not shooting through myself. But assuming solid torso hits on their target model - a 98th %ile male, it is conceivable it's correct. I have seen a few like that done with .45 ACP. It is important to note that there are many bodies that do not fit that mold.
Test were conducted at 3 yards range.


Back (http://www.angelfire.com/art/enchanter/pigboard.html#b4)

5) That this result is described as surprising may in itself be surprising, given the results of the 1904 tests (http://www.angelfire.com/art/enchanter/1904trial.html). The young modern engineers weren't aware of the earlier tests. They had to see for themselves and were surprised as they had been reading too much of the modern popular press.


Back (http://www.angelfire.com/art/enchanter/pigboard.html#b5)

6) That the bullet gets faster after it leaves the muzzle is a surprising and controversial result. The Army claims it's true and that a projectile doesn't require a barrel to accelerate. Alas, I cannot give an answer from personal experience so complete verification isn't entirely possible for me. I asked that question from the source, Army ammunition developers who developed that specific cartridge. The answer is theirs.
The Army guys [ballistic engineers] claimed to me that they measured it at distance increments of 10ft for a full 100 ft from the muzzle and so derived their statement. Projectiles can continue to accellerate as the Ammo plant test people showed me as the gas column is still pressing on the base of the projectile and still expanding in velocity as it too exits the barrel behind the projectile at a much higher velocity than the projectile. They claim this is why. Basically, they asserted to me that the effect of the explosion and propulsion from the gas column is still expanding and acting upon the projectile even as it leaves the barrel. The barrel also adds friction which tends to retard progress and once free of that friction it accelerates just slightly. I never had the ability to refute their claim as I lack the test bed they enjoy. But I just cannot dismiss those Army scientists out of

hand without verifying it myself. I spent too long in similar roles and I know how absolutely obstinate we are for testing.

http://www.angelfire.com/art/enchanter/pigboard.html
My only concern in this post is note #6. For years I have heard this claim and for years I have been with the majority of other people jumping all over the person who made the claim. Was I wrong? Does anybody know of any more recent testing of this phenomenon. It is counter intuitive to me but the explanation sounds plausible, barely plausible. I can't believe the effect would be substantial or easily tested but if somebody has modern data I sure would like to hear about it.

[matshock]

Maybe just a tiny bit once out of the barrel but that's purely academic. His description of the testing isn't real good either- why test at 100 ft?

Does a suppressor boost velocity a little over not having one?

Although I always did wonder what would happen if you had a rifle barrel that was only rifled for an inch or two at the chamber then smooth-bored and ever-so-slightly cone-shaped to keep pressure on the bullet but not let it make contact with the smooth part of the bore.

[NAPOTS]

I am pretty sure bullets are large enough and slow enough that they are still mostly governed by Newtonian physics so the only direction they will be accelerating in once they leave the barrel is down toward the center of mass of the earth.


Scratch that, they will also accelerate toward the shooter due to the effect of wind resistance.

F=ma

a=F/m

you have a constant force of gravity causing it to accelerate down

and a force of wind resistance that varies as a function of the velocity opposing the direction the bullet is traveling in.

I am not sure how to explain spin drift. It might be due to shear forces from the air due to rotation

[AK-J]

It might be possible that the bullet slightly continues to accelerate once it leaves the barrel as long as the gases are still pushing on the projectile, but I imagine it might be for a few feet at most.

[NAPOTS]

It might be possible that the bullet slightly continues to accelerate once it leaves the barrel as long as the gases are still pushing on the projectile, but I imagine it might be for a few feet at most.

I agree but upwards of 100 feet or even 10? no f*cking way.

[Uncle Scary]

Bullets accelerate after they leave the barrel???

If you fire them at the ground from a high vantage point. Until they reach terminal velocity or hit the ground.

[old Grump]

If you fire them at the ground from a high vantage point. Until they reach terminal velocity or hit the ground.
Even a tiny standard velocity 40 grain bullet from a 22 cal rifle is going faster than it would ever get no matter how far it fell. I don't think gravity will increase velocity in that instance.


It might be possible that the bullet slightly continues to accelerate once it leaves the barrel as long as the gases are still pushing on the projectile, but I imagine it might be for a few feet at most. I'm thinking inches at most and my reasoning is that the gas won't be concentrated in a narrow column once it leaves the muzzle of the barrel. Gas moves out in every direction where the pressure is lower leaving less gas in the column to push the bullet. Every fraction of an inch there is less gas and less pressure to push on the base of the bullet. Unless the charge was a small one and completely consumed before the bullet reached the end of the barrel I fail to see how friction would play much of a role unless the bore was undersized. Even then the bullet should continue on at the same velocity when it leaves untill atmospheric drag slows it down. I read it but I'm having a hard time swallowing it.

[NAPOTS]

I wouldn't swallow it either. It would be an easy enough experiement to put together if you had a couple of chronographs.

[alismith]

Since the bullet is a projectile and has no power source of its own, I believe that physics describes it's velocity as decreasing forward motion and increasing downward motion once it leaves the barrel. As soon as the effect of the propellant on the bullet is gone, it loses forward velocity. (There may still be a push from propellants a few millimeters from the muzzle as the propellents still push forward, but that would be about it. Once the gases exit the barrel, the push is over.)

The only way it could increase velocity in a forward direction is for it to have it's own power source that would accelerate it forward.

I'm not sure I would trust a testing team that stands to gain something from the positive results of the tests it performs.

[Dan Morris]

Since the bullet is a projectile and has no power source of its own, I believe that physics describes it's velocity as decreasing forward motion and increasing downward motion once it leaves the barrel. As soon as the effect of the propellant on the bullet is gone, it loses forward velocity. (There may still be a push from propellants a few millimeters from the muzzle as the propellents still push forward, but that would be about it. Once the gases exit the barrel, the push is over.)

The only way it could increase velocity in a forward direction is for it to have it's own power source that would accelerate it forward.

I'm not sure I would trust a testing team that stands to gain something from the positive results of the tests it performs.


To me, this would be impossible without the power source...like the old GyroJet....it flopped.
Dan

[AK-J]

I don't buy the idea that it still accelerates 10's of feet from the muzzle. Have any of y'all seen super high-speed video of a bullet leaving the barrel? There is a column of gasses directly behind the projectile for quite a distance. That leaves me to find it plausible that it could continue to accelerate for a few feet or less after leaving the barrel.

[old Grump]

I don't buy the idea that it still accelerates 10's of feet from the muzzle. Have any of y'all seen super high-speed video of a bullet leaving the barrel? There is a column of gasses directly behind the projectile for quite a distance. That leaves me to find it plausible that it could continue to accelerate for a few feet or less after leaving the barrel.
That column is also expanding at an exponential rate as it tries to flow towards the lowest pressure. I would be willing to bet that column of gas directly behind the bullet is just filling in the vacuum created in the wake of the projectile. In other words being dragged, not pushing. But I'm no physicist and its been years since I slept in a Holiday Inn so I admit to being ignorant.

[sisyphus]

Other than the possible effect of gas pushing after the projectile leaves the barrel (stated above) the only way my feeble mind can envision any acceleration is with the RAP projectiles used in artillery and naval gunnery..........or those strange little Gyrojet projectiles that went defunct about 45 years ago.

[swampdragon]

I can see for a split send or two how a bullet could accelerate.
Once it leaves the barrel, there is no more friction on the bullet.
The gas would still be pushing it though as it exits also.
But like already said, I can only imagine that making a difference for a few inches or so.