Things that make you go Hmmm

[Afy]

Thinking about Tracers, which to my understanding have a compound that burins in the base of the bullet. This threw up a couple of random questions in my mind:

1. Does it affect accuracy along the lines of what was called Base Bleed ammunition in the 90's primarily for artillery.
2. Does it affect velocity. As the bullet goes down the trajectory the compound will burn off.. making the bullet lighter. Also does the burning compound have an effect on velocity?

Hmmm...

 

[DanTheFarmer]

Hi,

Tracers for small arms normally have the burning compound on the nose of the bullet.

The trajectory of the tracer is slightly different than a conventional round. Machine gun ammo is often packed "4 and 1", 4 rounds FMJ, 1 tracer, 4 FMJ, 1 tracer, and so on until the end of belt. The POI of the tracer will be slightly different than the 4 ball rounds in between. From this you can guess the velocity will differ slightly as well.

Base Bleed is a pretty neat idea. The burning compound at the base of the artillery shell creates a long "virtual boat tail" to the shell and reduces the overall drag, thus extending the range. It is related to drafting in NASCAR. But since the burning compound is on the nose of small arms tracers they don't benefit from a base bleed effect.

I hope you don't mind a little side track here but when the Bradley fighting vehicle was developed it had several firing ports. The weapons in these firing ports were essentially M16 without stocks and fixed to ball mounts. One of the early ideas was to not have any sights on the weapons, bump up the rate of fire to 1200 rpm or so and load with only tracer. The gunner would then walk the red stream of light onto the target. That idea didn't last but it would have been cool to see!

Dan

 

[NCsmitty]

Tracers for small arms normally have the burning compound on the nose of the bullet.

I don't believe that is correct, it is base mounted and ignited by the powder of course. That is, unless things have really changed in the past few years. The 223 tracers that I have carry the tracer compound in the base of the bullet.



NCsmitty

 

[ljnowell]

Tracers for small arms normally have the burning compound on the nose of the bullet.

hmmm, thats pretty well counter to everything I have ever read. I was always under the impression that they had a base of the bullet that contained phosphorus, or maybe magnesium. Got a link or something about tracer bullets having the tracing compound in the nose?

 

[DanTheFarmer]

Oops!

It looks like I was mixing up the red paint on the tip of the bullet to indicate that it is a tracer with the actual tracer compound itself.

Thanks for the correction.

Dan

 

[webfox]

Once a projectile leaves the burning gases of the propellant (end of barrel), it does not accelerate any more. It only slows down and drops toward Earth.

Unless the tracer powder burns faster than the speed of the bullet, there won't be any propulsion.

Now, as the bullet loses the weight of the tracer compound, it becomes lighter and its trajectory will change upward compared to a non-tracer round that retains its original mass. It might hit higher up, but it doesn't hit faster or harder. It's traveling at the same speed it would at impact, it's just a little lighter by then.

The difference in tracer/FMJ will depend on the mass of the tracer compound compared to the mass of the original bullet and the distance fired.

It's probably negligible for large ammo, like that used in aerial dog fights. I can't speak for smaller rounds, but I think lead is 6.7 times as heavy as phosphorus and 8.5 times as heavy as magnesium, so considering the amount of tracer compound, you're probably looking at a final difference in weight just a few percent less than what you stared with in the whole projectile. So, considering you're not looking at long, long ranges, trajectory difference is probably negligible for its use.

 

[medalguy]

I shoot a lot of mixed ball/tracer in machine guns, and thre's no measurable difference in impact out to 5-600 yards, unless you were to use a machine rest. But it's not designed to be that accurate, just a guide for machine gunners to see where their bullets are impacting and to correct their fire.

I suppose if you used a rest and really tried to measure the accuracy you could see a difference but I suspect it would be negligible.

And yes the tracer compound is indeed in the base of the bullet.

 

[NeuseRvrRat]

Now, as the bullet loses the weight of the tracer compound, it becomes lighter and its trajectory will change upward compared to a non-tracer round that retains its original mass.

i disagree. the effect of gravity (9.8 m/s^2 downward) will be the same no matter what the mass of the projectile. heavier bullets exhibit more "fall" than lighter bullets in the same caliber/cartridge simply because they are (usually) travelling slower and have more time to fall. that is, more time for 9.8 m/s^2 downward to act upon them. now, with losing mass, there would be some difference in air resistance, which may increase or decrease ballistic coefficient, which may cause the bullet to fall more or less than one that retains it's entire mass. this effect could be large or small, depending on how much BC changes. i don't think it would be significant.

now, that is assuming that the tracer is burned outside of the barrel. the amount of the tracer mass that is burned inside the barrel would change mass, which would change the muzzle velocity, which could affect POI. again, i would guess that this difference is negligible. probably no greater than the mass tolerance for the bullet anyway.

if the tracer projectile has a different weight or BC than the normal projectile, then POI would definitely change, but the OP asks about losing weight during flight, which would not affect POI unless your drag coefficient changes significantly.

if you want proof that gravity is gravity, regardless of mass, watch the videos of the astronauts dropping a hammer and a feather on the moon: http://www.youtube.com/watch?v=5C5_dOEyAfk

and if you don't think we actually landed on the moon, there's stuff like this: http://www.youtube.com/watch?v=_XJcZ-KoL9o

hypothetically, if you can propel a 40 gr projectile and a 200 gr projectile of the same caliber with the same drag coefficient at the same velocity, they would shoot to the same POI

physics is fun!

 

[USSR]

Tracers for small arms normally have the burning compound on the nose of the bullet.

Nope. The compound is inserted in the base of the bullet, and in the case of the M25 tracer bullet, covered with a brass "cap".

Don

 

[Owen]

The tracers do have a slightly different trajectory. IIRC, it's about 1m different at 500m

 

[Vern Humphrey]

Now, as the bullet loses the weight of the tracer compound, it becomes lighter and its trajectory will change upward compared to a non-tracer round that retains its original mass.

i disagree. the effect of gravity (9.8 m/s^2 downward) will be the same no matter what the mass of the projectile.

The burning of the tracer element reduces the mass of the bullet.

The trajectory is based on three factors -- gravity (which is the same for all bullets), drag (which is the same for identical bullets) and momentum. Momentum tends to keep the bullet moving in a straight line at a constant speed. Drag slows it down. As the bullet loses mass, it loses momentum, and is slowed more by drag than an equivallent bullet of full weight.

Tracers are designed to match trajectories of ball and/or AP rounds, but they do this by compromise -- they are not a perfect match for the full trajectory, and at longer than the design range they will fall short of ball or AP.

 

[NeuseRvrRat]

Momentum tends to keep the bullet moving in a straight line at a constant speed. Drag slows it down. As the bullet loses mass, it loses momentum, and is slowed more by drag than an equivallent bullet of full weight.

very good point and something i overlooked. one would expect that loss of momentum to result in a lower POI, correct?

 

[Vern Humphrey]

Correct. The reduced momentum-to-drag ratio would result in a lower POI, compared to a standard bullet.

 

[Hondo 60]

Not sure if tracers affect velocity, I haven't been brave (or dumb?) enough to shoot them a crossed my chrono.

I do know that it doesn't affect accuracy (or at least not much). I can hit bowling pin shaped metal targets set up on top of a berm 300 yards away with or without tracers in my AR15A1.

(pretty cool to watch 'em travel - especially at dusk)

 

[Afy]

All good info. Was just a random thought that crossed my mind.

 

[Vern Humphrey]

Not sure if tracers affect velocity, I haven't been brave (or dumb?) enough to shoot them a crossed my chrono.

I do know that it doesn't affect accuracy (or at least not much). I can hit bowling pin shaped metal targets set up on top of a berm 300 yards away with or without tracers in my AR15A1.

(pretty cool to watch 'em travel - especially at dusk)

Tracer burn-out varies with the intended use of the ammunition, but usually is around 1,000 meters. At 300 meters, the effect of reduced mass is almost unnoticeable.

 

[webfox]

I was saying that the trajectory changes ***compared*** to a heavier round which was not losing its mass.

 

[kingmt]

+1 Vern

All this math made my head hurt. I get POI but the group opens up. Pressure spikes at a lower charge also but probably due to less case capacity.