Bullet contrail was unreal today (5.56)

**jbdesigns** · 05-22-16, 21:14

I went to my gun clubs very modest outdoor range with my best friend and his three college aged girls. Plus on extra girl friend and a boyfriend.

I set up on out single lane range at the 100yd mark. I was giving them all their first taste shooting an AR-15 rifle. Our range is in a marsh area. It didn't feel very humid at all, about 70F.

However while observing one of the shoot typical ball 5.56 at my steel, I saw what looked like the bullets exploding or hitting something mid flight. Sometimes I'd see a burst of mist only 20yds from the muzzle. Other times I would see a huge "smoke" trail all the way to the target.

At first, I thought maybe the bullets were exploding, you know from too much spin. But that thought went away because I would hear the steel ring. Then I thought the rounds were hitting bugs. But there weren't any out today. So we surmised it was simply a very visible contrail. I mean it was like they were trailing a smoke trail. I've never seen this before.

I've seen videos of guys shooting very long range and the camera in the spotting scope would pick of the faint shock wave trail. But today, the rounds looked like they were trailing smoke. It was crazy cool. I even tried a different round, some hand loads since at first I thought the billet was coming apart. But the hand load 53gr vmax did it too.

Has anyone seen this? Would I need near 100% RH to get this? I'm pretty sure it wasn't anywhere near that humid. I'm in western NY, not Florida.

Just bringing it up since it was so unusual and strong of a trail. The ground was swampy so near the ground level maybe it was much more humid. It's marsh on either side of the shooting lane. But the lane of grass doesn't usually ever fully dry out. I'm thinking there might be a micro atmospheric condition within the first 8 feet above ground before the surrounding air soaks up the moisture and disperses it more.

Just a curios observation. Wish I had video of it

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**jpmuscle** · 05-22-16, 21:22

OP, where in Wny?

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**markm** · 05-22-16, 21:26

Originally Posted by jbdesigns

Has anyone seen this?

My buddy has an A1 20" gun that traces ridiculously with a smokey bizarre vapor trail. It's the most unusual thing. Not sure if it's the same thing, but it's remarkable.

**jbdesigns** · 05-22-16, 21:51

This was a 20" upper in a A4 configuration. It is helpful to know you have seen it.
It was the most unusual and bizarre thing. My sons and the others all saw it too. At the time, it was one of the new shooters so all shots were NOT hitting their mark and therefore, the trails were marking the misses too.

In the Southtowns of Buffalo. Boston Valley Conservation Society (bvcs) is the club.

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**Kdubya** · 05-22-16, 22:35

I saw something similar to what you're describing in one of tnoutdoors videos (below), and think it would be pretty awesome to see in real life. The "trails" can be seen at about the 3:00 mark. I don't think he realized it until after viewing the footage, so that's pretty cool that you were able to catch this in real time. How would you say this compares to what you experienced today?

https://m.youtube.com/watch?v=ZxpnWftvCTo

**P2000** · 05-22-16, 23:04

Sounds similar to what happens on aircraft sometimes. I've seen pictures of propeller tips leaving a corkscrew pattern in the air, and wingtip vortices that last a ways. Must be related to humidity?

**Rayrevolver** · 05-22-16, 23:56

Originally Posted by P2000

Sounds similar to what happens on aircraft sometimes. I've seen pictures of propeller tips leaving a corkscrew pattern in the air, and wingtip vortices that last a ways. Must be related to humidity?

Can happen on the ground too:

**Skyyr** · 05-23-16, 01:30

It happens when the relative humidity is very high. You see it more commonly with aircraft propellers, as someone else here mentioned.

At any given time, the air can only hold some much humidity before the humidity condenses out as visible water droplets. How much water is in the air is measured as relative humidity. Once relative humidity hits 100%, the air cannot hold any more water and any additional water in the air over the amount that the air can contain condenses out as water droplets. These water droplets are very, very small, and can still stay suspended in the air; however, they become visible as trails, clouds, etc.

Enter aerodynamics.

When a bullet is travelling through the air, it is aerodynamically generating a very, very slight amount of lift (or an area of low pressure, technically). The lift itself is mostly cancelled out by other forces, but the low pressure remains. When the pressure of the surrounding air is lowered, the temperature drops; when the air temperature drops, the air can hold less water due to the lessened energy state of the air, but the amount of absolute water vapor in the air remains the same. This has the effect of raising the relative humidity.

On days when the relative humidity is very, very close to 100%, quickly dropping the air pressure will cause the water vapor to condense out. As mentioned earlier, this is commonly seen with aircraft, but can also happen with bullets, arrows, and anything else that has or creates a lifting surface or area of low pressure as it travels through the air.

On a day like this, the bullet will create a contrail of sorts that will spin with the bullet due to the wake turbulence the bullet is leaving behind. Depending on the atmospheric conditions, the amount of time it's visible is usually very brief, but can vary. Once the bullet has left the immediate area (which is measured in milliseconds given the speed of the projectile), the air pressure will return to normal and the water vapor will evaporate back into the air as the temperature rises back to the ambient temperature.

Given that you were in a marshy area (inherently high relative humidity) on a cool, stable day, this is likely what you saw.

Too bad you didn't get film of it - would've made for some good YouTube.