Vapor trial

[Boisblancboy]

For those of you that have seen a vapor trail lets here the conditions. I've tried but never had an luck seeing it. Does the distance is the shot matter, weather conditions, etc?

[247sniper]

Hi mate, I have noticed the vapour trail from my bullrts on video quite a few times recently.

However last night I saw the vapour trail through the scope while shooting targets.

Conditions were,

Shooting small balloons at 400 yards with the sun going down in front of me in very windy conditions. Temp was around 8 oc.


From my experience longer range, past 300 yards, and sunny conditions you will see vapour trial. It's good because you can spot your shot, even your hits with better precision.

Hope this helps

Steve.

[csand]

While taking a break from deer hunting last year we shot plastic water bottles with a .264 LBC-AR and a Cooper .20 VT . It was late afternoon, sunny and about 50 degrees F. and possibly 40-50% R.H.. All shots were 500 yds. The shooters were lying on the ground and the vapor trails were easily seen by all members through a spotting scope that was positioned "directly" behind and just above the shooter. I recall that the vapor trails did not start until about half way to the target. It was very cool!!

[247sniper]

Has anyone else seen the vapour trail through their own scope while shooting?

Fantastic to watch.


Steve.

[Jim White]

Has anyone else seen the vapour trail through their own scope while shooting?

Fantastic to watch.


Steve.

Yes...with my 204 & 17 HMR's.

[Boisblancboy]

Hopefully one of these days I'll get a glimpse at it!

[Sth Oz Dan]

http://www.youtube.com/watch?v=uiH1RhOdGWU
Not sure if this is vapour trails or sonic distortion, but worth a look.

[Fred_C_Dobbs]

What's in Sth Oz Dan's video, I think, is trace, not vapor trail. Vapor trail is weather-dependent and a fairly rare phenomenon. You need a high relative humidity, or a dew point close to the ambient temperature. Bullet trace, OTOH, is caused by the shockwave following the bullet changing the air's index of refraction, and occurs every time someone shoots a transonic or faster bullet. But it takes a trained eye and decent optics to see it consistently. Sniper spotters rely on it to call the shooter's adjustments.

[Darkker]

Yes distance matters, as far as picking up the signature.
The best chance at seeing it here(low RH) is to the side of the shooter, about 3 feet; beyond 200 yards. Larger calibers tend to be easier to see as well.
The trick(through a scope) is to have the target in sight, and wait for it to enter you FOV.
That is how I track shots by friends when sighting in. Cheap scopes that don't have very clear, true color also makes it difficult.

[Wrangler John]

The vapor trail I refer to is from the bullet coming apart from excessive velocity. It happened when I used Sierra Blitz bullets (or other bullets designed for low velocity cartridges such as Hornet bullets) in the .22-250 or .220 Swift loaded to velocities in excess of 3,800 fps. When fired there would be a little smoke trace in the air that was visible regardless of lighting conditions. Ground squirrels within 75 - 100 yards would be creamed, but beyond that the bullet self-destructed not even reaching them. Take a good solid hold and fire, the bullet arched out trailing a little swirling grey smoke trace and suddenly it vanished, the squirrel never moved or gave any indication it was perturbed at all. At the range, some bullets will not reach the target, or print keyholes and gross flyers when they do. The .257 Ackley Improved loaded with bullets designed for the .25-20 would do the same thing.

Bullets, especially .224" diameter, at the time were labeled for velocities below 3,500 fps, Medium Velocity and High Velocity. Better construction made this less likely today, but they can still be smoked if enough effort is made. The lead free compressed powdered metal core bullets, such as the Varmint Grenade seem to be immune to this, possibly because the core is a solid instead of soft lead that can become plastic at high rotational speed and velocity. At least I have driven them up to 4,200 fps with no failures and tiny groups. Plastic tips also seem to have helped keep things together.

One other shock wave phenomena became apparent with the .204 Ruger. Because the recoil is so modest, I am able to see the shock wave from impact coming off the target varmint. It appears like a smaller version of those blast waves propagating from a bomb detonation. It's a little harder to see, with back lighting helping, but there is a shock wave produced by impact. Maybe it's accentuated by the blow up of a Varmint Grenade and the dust and fur flying, but it was quite amazing the first few times I saw it.

[Darkker]

The vapor trail I refer to is from the bullet coming apart from excessive velocity. It happened when I used Sierra Blitz bullets (or other bullets designed for low velocity cartridges such as Hornet bullets) in the .22-250 or .220 Swift loaded to velocities in excess of 3,800 fps. When fired there would be a little smoke trace in the air that was visible regardless of lighting conditions. Ground squirrels within 75 - 100 yards would be creamed, but beyond that the bullet self-destructed not even reaching them. Take a good solid hold and fire, the bullet arched out trailing a little swirling grey smoke trace and suddenly it vanished, the squirrel never moved or gave any indication it was perturbed at all. At the range, some bullets will not reach the target, or print keyholes and gross flyers when they do. The .257 Ackley Improved loaded with bullets designed for the .25-20 would do the same thing.

Bullets, especially .224" diameter, at the time were labeled for velocities below 3,500 fps, Medium Velocity and High Velocity. Better construction made this less likely today, but they can still be smoked if enough effort is made. The lead free compressed powdered metal core bullets, such as the Varmint Grenade seem to be immune to this, possibly because the core is a solid instead of soft lead that can become plastic at high rotational speed and velocity. At least I have driven them up to 4,200 fps with no failures and tiny groups. Plastic tips also seem to have helped keep things together.

One other shock wave phenomena became apparent with the .204 Ruger. Because the recoil is so modest, I am able to see the shock wave from impact coming off the target varmint. It appears like a smaller version of those blast waves propagating from a bomb detonation. It's a little harder to see, with back lighting helping, but there is a shock wave produced by impact. Maybe it's accentuated by the blow up of a Varmint Grenade and the dust and fur flying, but it was quite amazing the first few times I saw it.

Although reloading books use the word "Velocity", that IS NOT what causes core/jacket slippage, and NOT what destroys bullets. It is the centrifugal force, from the RPM of the bullet.
MV * 720 / Twist = RPM
I have a small listing of the RPM limits for 22-cal Varmint bullets, as provided by the manufacturers here:
http://www.shootersforum.com/ballistics ... imits.html

[Fred_C_Dobbs]

It's actually more often caused by the bullet's lead core melting in flight. This was proved in 2007 in testing conducted by Eric Stecker of Berger Bullets.

In a nutshell, first Berger hired scientists at M.I.T., who modeled the firing stresses and confirmed that the bullet's friction against the bore can in fact heat the skin of a bullet to a temperature in excess of the melting point of lead (copper melts ~1300° hotter).

With that information in hand, Berger made two batches of 6.5mm test bullets, around 450 examples of each, one with a thin jacket and the other with a thick jacket. They loaded all ~900 bullets onto Lapua 6.5x284 brass charged with 49.5 grains of H4350 and went to the range. Then they fired the rounds at regular intervals (~90/hour) at a target @1000 yards, which they believed would provide enough time of flight to give the bullets ample opportunity to fail. Each firing was monitored by two observers. Only if the two observers agreed did they record that bullet as "failed in flight."

None (0) of the thick jacketed bullets failed but 39 of the thin jacketed bullets were observed to have "exploded" before reaching the berm. They even blew out the primers on several of the thick jacketed rounds, which hints at the pressure behind those loads, but none of them failed.

Their conclusion was that the thick jacketed bullets did not fail because it took the high skin temperature too long to migrate across the jacket and reach the lead core. With the thin jacketed bullets, OTOH, it could cross the jacket in less time than it took the bullet to reach the target.

This is Eric Stecker's (then Berger VP and since Walt's successor) summation of the testing:

Failures have several causes. The most common is produced by the core melting. The core melts because it gets too hot. The core gets too hot because of the FRICTION between the rifling and bearing surface. This has been proven to be the hottest part of the bullet as it moves through the barrel. This area has been shown in high speed, infared images reaching tempuratures at the melting point of lead.

Other causes for failure are excessive RPM. Since most shooters use factory (bullet or barrel) recommended twist rates failures due to excessive twist rates are rare (but do happen).

Rarer still is a failure caused by extreme barrel issues (damaged bore) extremely poor loading practices (damaged bullet) or extremely poor cleaning practices (which further increases friction).

Another extremely rare cause is related to bullet production issues. Bullet construction that is poor enough to result in bullet failure (and where bullet failure would not have occurred for any other reason) can theoretically occur in situations where standard QA and production procedures are ignored almost completely. I am sure that this is possible but is as unlikely as I can imagine (from all bullet makers).

These reasons for failure are true for all bullets. Bullets from every maker can experience failure under the right (or wrong) conditions. Recently, Sierra has made public that they are discontinuing the production of 6mm 117 gr DTAC due to repeated failures. I do not mean to pick on Sierra but this is a recent example. ALL BULLET MAKERS HAVE BULLETS THAT FAIL AND MOST FAILURES ARE CAUSED BY THE MELTING OF THE CORE.

Maybe "melting" is to strong a term but all the lead has to do to cause the bullet to self-destruct is to get hot enough that it becomes the tiniest bit plastic. Then centripetal force does the rest. Eric's test bullets were spinning more than 4000 time a second (3000 fps MV from a 1:8.5 barrel), which is a whole lotta G-forces, even if it's only a 1/4" object.


The long version of the story is in this thread at Benchrest.com.

[204cat]

1/5" object.

[Sth Oz Dan]

1/5" object.

Took a little while for that penny to drop.

[Fred_C_Dobbs]

1/5" object.

6.5 mm = 0.2559"

The barrels they used were .256" and .257".