Guns are fun w/ sonic booms

[StreetScooby 5]

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... first rising upward,

From lift? Is that for all bullets? How far out before they start dropping?

We are all engines of karma

[1969912 0]

The "wake" seen is most likely due to a change in the refractive index of the air around the bullet caused by the air being compressed by the shock wave, i.e. the compressed air around the bullet has a higher density than the AIR not affected by the bullet.




edited typo - shoulda been in typing class in 7th grade, and not playing hooky to build go-karts!

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[JohnRich 4]

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... first rising upward,

From lift? Is that for all bullets? How far out before they start dropping?

No, it's not lift. Rifle barrels are angled upward to shoot the bullets like angled cannon fire, just not as pronounced.

Think of a gun barrel, with sights placed on top of the barrel. The line of sight is therefore a few inches above the bullet. If the barrel was parallel with the earth, the bullets would drop from gravity and never intersect with the line of the sights which are located on top of the barrel. In other words, you would never hit what you are aiming at - you would always be too low.

To rectify that, the barrel is angled upwards. Thus, the bullet passes upward through the line of sight, usually at about 25 yards, and then some distance out curves back downward through the line of sight again, a second time. To hit what you are looking at, since the bullet curves up and down, and your eyeball makes a straight line, you have to "zero" the rifle. That means that you adjust the sights so that the downward curve of the bullet intersects with the target that you are looking at in a straight line. Lining up those two things can prove tricky. And of course, it changes over distance. So you have to really know your gun and the bullet ballistics, to know how to set the sight elevation adjustment.

Once I learn all this for a rifle, I write it down on a piece of paper and tape it to my stock. For example, with my .308 M1A, which I shoot at 200, 300, 600 and 1,000 yards, my corresponding elevation "come up" clicks are: 8, 11, 25, and 48. Those represent the upward angle of the barrel which causes the downward plunging bullets to intersect the target exactly where I'm looking at it. Hopefully.

And those numbers hold true only for one set of variables. If I change my ammo load, all bets are off. I recently shot a batch of ammo with another measly .5 grain of gunpowder (trying to keep my bullets supersonic out to 1000 yards), and it changed the point of impact by a whopping 40" at 1,000 yards. Every type of ammo can be different. Every batch of powder, even of the same type, can be different. Different air temperature has an effect. And so on. It's a never-ending challenge trying to stay on top of your zeros. Every time I think I've got them locked-in just right, my first shot in a new match will be off...

It ain't nearly as easy as Hollywood makes it look.

[StreetScooby 5]

Great explanation! Thanks!

We are all engines of karma

[JohnRich 4]

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The "wake" seen is most likely due to a change in the refractive index of the air around the bullet caused by the air being compressed by the shock wave, i.e. the compressed air around the bullet has a higher density than the AIR not affected by the bullet.

Now that's something that I had not considered. So the light is bent a bit as it passes through denser air, causing a change in the appearance? (I'm thinking of how light is refracted at sunset to produce orange light as it comes through the atmosphere...)

[dorbie 0]

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The "wake" seen is most likely due to a change in the refractive index of the air around the bullet caused by the air being compressed by the shock wave, i.e. the compressed air around the bullet has a higher density than the AIR not affected by the bullet.

Now that's something that I had not considered. So the light is bent a bit as it passes through denser air, causing a change in the appearance? (I'm thinking of how light is refracted at sunset to produce orange light as it comes through the atmosphere...)

That's mainly atmospheric scattering and absorption.

A better analogy is a stick visually bending when you dip it in water. Or heat haze when the air shimmers above hot terrain.

[kallend 2,175]

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The "wake" seen is most likely due to a change in the refractive index of the air around the bullet caused by the air being compressed by the shock wave, i.e. the compressed air around the bullet has a higher density than the AIR not affected by the bullet.

Now that's something that I had not considered. So the light is bent a bit as it passes through denser air, causing a change in the appearance? (I'm thinking of how light is refracted at sunset to produce orange light as it comes through the atmosphere...)

the phenomenon can be greatly magnified using the Schlieren effect.www.rit.edu/~andpph/text-schlieren.html

...

The only sure way to survive a canopy collision is not to have one.

[JohnRich 4]

You got me doing a Google search for a photo of a bullet wake. The first things I came up with include this.

Unfortunately, it's a still photo of one split second in time. When watching live shooting through a scope, you see a continuous series of "V" shapes like that all stacked together. Sort of like: >>>>>>>>>> And all that V-shaped wake is like a curving arrow following the path of the bullet to the target. In need of a high-speed video clip!

I'm becoming convinced that this is light refraction rather than heat waves. But I'm not sure, because their is a hot bullet involved...

[1969912 0]

It is due to light having a slightly different velocity through different materials (or air at different densities). When the light passes from one material (or density) to another it gets refracted, or bent, in another direction. A mirage or the shimmering you see over a hot runway is caused by the light travelling through the varying densities of air kind of boiling above the runway. I've never seen the phenomenon with a bullet in real life, but it must look cool, as long, that is, if you are on the right end of the bullet's path!

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[Tonto 1]

Lets accept the misnomer "Silencer" instead of the more correct "Suppressor"

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I know John knows a lot more about this than I, but I don't believe a 22 pistol round will break the sound barrier.

Wrong. All High velocity and some standard velocity ammo will break the sound barrier out of even moderate barrel lengths. (3 in)

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A high powered rifle will. That's why a silencer won't work on any weapon if the bullet is moving too fast.

Wrong. Look at the calculation both you and John quoted. You need the sound of the crack AND the boom to be able to calculate distance and heading. A silenced rifle will crack - but no boom - so you know you're being shot at (Duh) but you don't know from where.

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One guy tried to tell me he had a silencer on a 300 magnum. I had to laugh at that one. I don't know a whole lot about silencers but I don't think they will work except on a very slow moving bullet. Correct me if I'm wrong on this. It's been a long time since I've had training on this....Steve1

You're wrong on this. You are correct that you don't know this subject.

There are three primary problem noises associated with bullets.

Problem
a) The gunshot
b) The bullet
c) The target

Solution
a) is dealt with by using a silencer
b) is dealt with by using subsonic ammunition
c) is difficult. Shooting meat results is a loud "smack" sound, akin to an open handed strike. Smaller callibers, lower velocity ammunition and careful shot placement can help, but these situations are only usually a problem for sentry take downs, and there are simpler and better ways of doing that than using a gun.

Some issues are more complex than others. Using a silenced rifle with supersonic ammo to shoot from within a room out of the window will still reveal the sound source as the sonic boom echo's within the room in the same way the origional poster mentioned the bridge pillars, thus compromising the shooter. The subsonic equiped shooter does not face this problem, but with their choice of lower energy ammunition would face an increased need to take the shot from a shorter range.

A silenced supersonic round can cause a great deal of confusion. If the round passes North to South between 2 secret service agents who are both facing North, 30 feet apart on its way to the target, the one on the West side will hear the sound as having come from the Southeast, and the one on the east side will hear the shot as having come from the Southwest due to the >>>> effect mentioned in John's post. Outer circle teams need very good training and coordination to correctly pin down the site of the shooter and will usually fail to do so if the shooter has deliberately chosen a less than ideal position to shoot from, as most security personel will use optimum as a guide to find a shooter when faced with a trucated timeframe.

t

It's the year of the Pig.

[steve1 5]

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You're wrong on this. You are correct that you don't know this subject.
/reply]

That could be true. Whatever I know about silencers I was taught in S.F. weapons training 30 years ago. We were told that to silence a round it must be sub-sonic. Maybe that is crap. Maybe it was only true for the silencers they had then, or maybe our instructor was just full of it. This isn't the first time I was lied to in the army.
I do know quite a bit about reloading though. I was always told that if you underload a high powered rifle enough it can create shock waves within the case that could cause the gun to blow up. That is why I don't see how you can take a 300 magnum and load it slow enough to work with a silencer. But then again, if you are saying that a high powered rifle doesn't need to be downloaded to still work, with a silencer, I will stand corrected on this also.

I don't mean to be a smart alleck...I'm learning something new from this....Steve1

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[Tonto 1]

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We were told that to silence a round it must be sub-sonic.

To silence the round, yes. To silence the weapon, no.

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I do know quite a bit about reloading though. I was always told that if you underload a high powered rifle enough it can create shock waves within the case that could cause the gun to blow up.

This is partly correct, if you use the same weight bullet. If you use lighter bullets, or slower burning powders or integrally suppress the weapon to prevent the pressures from becoming too high these problems can (and have) been overcome.

As for the one shot silencer... well, it's going to have to be a monster potato to do the job, and it will create a lot of mess and not keep thinks very quiet. There is a LOT of science in silencers. Hollywood have done a fine job of convincing most people that a 45 can be silenced with a silencer the size of a roll of dimes. The truth is they are many, many times that size. With pistols one faces several additional challenges such as mechanical noise (The slide clacking back and forth) and chamber noise (when the slide allows some of the gasses to vent (Noisily) through the ejector port.) Both are usually solved with a slide lock (negatives are a lot of force transfered to the frame), or even just a thumb resting on the back of the slide for a .22.

t

It's the year of the Pig.

[JohnRich 4]

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A silenced supersonic round can cause a great deal of confusion... If the round passes North to South between 2 secret service agents who are both facing North, 30 feet apart on its way to the target, the one on the West side will hear the sound as having come from the Southeast, and the one on the east side will hear the shot as having come from the Southwest due to the >>>> effect mentioned in John's post.

Hoo-boy! We're really getting complicated now... You're making my head hurt trying to figure out how to interpret that pattern, as a single downrange observor, to figure out where the shooter would be.

[JohnRich 4]

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I do know quite a bit about reloading though. I was always told that if you underload a high powered rifle enough it can create shock waves within the case that could cause the gun to blow up.

I haven't heard the "shock waves" thing, but underloading rifle cases is not a good idea. If the powder doesn't fill the case, then when the cartridge is laid down horizontally in the chamber to fire it, the powder can spread out on the bottom half of the case. Thus, when the primer fires, the flash spreads over the entire surface area of the available powder, igniting it all at once across the lengthwise cross- section, instead of burning from one end to the other as usual. This effect can actually cause a pressure spike that is greater than a case with much more powder in it. That's my understanding.

Then the other extreme is filling the case so full that seating the bullet "crunches" the powder down and compresses it. Also bad.

I keep a little plastic box in my reloading bench with my mistakes in it, to remind me that I'm playing with fire. It has split cases, head separations, upside-down primers, collapsed shoulders, blown primers, etc. I've managed not to blow my face off though, or damage any guns.

[steve1 5]

[JohnRich 4]

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I have a tendency to load them borderline too hot.

Eeek! We have a shooter or two in our club that have that tendancy too. I try to be several shooting stations away from them in a match.

I don't exceed the recommended maximum load. When developing a load, I start low, and work my way up, producing cases in batches of five, in half-grain increments. I write the charge weight on the cases with magic marker. Then I go test shoot, starting with the lowest charges, and working my way up. I watch for signs of over-pressure, and for when I find a load that has a sweet spot with the tightest groups. If I start seeing flattened primers or something, I stop right there.

I had a dilemma a few months ago. I was already at the max recommended accuracy load for .308 with IMR4895 powder, and yet my bullets were subsonic at 1,000 yards. Everyone was saying to add more powder. Nope, wouldn't do it. I was at a loss for what to do next. Then after I used up that batch of powder and ordered a new batch, using the same load, suddenly my bullets were supersonic again all the way out to the 1,000-yard target. So apparently I just had a batch of powder that produced less pressure than it should have. So, lesson learned: powders can vary significantly from batch to batch, even for the same powder type.

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Probably one of the stupidest thing I've done to date... Ended up with a face full of hot gas on the first one I fired... This tore the base off of the case and a gun-smith had to get the rest of the case out of the chamber.

I keep "stuck-case" removers in my calibers in my gun tool box which goes to the range with me. It's a plug with a base the size of the caliber, and a couple of fingers that reach in and grab the edge of the separated case stuck in the chamber. You just close the bolt on it, and then re-open the bolt - it extracts the piece of case with it. They come in really handy every rare once in a while, and impress other shooters with your gizmos.

I also learned real quick with reloading to buy a stuck case remover for my re-sizing dies, for when you don't use enough lube and the pressure jams a case up inside the die. I use that tool a lot...

[1969912 0]

How well do real, professional supressors work as far as silencing the noise from the barrel? Are they as quiet as they seem to be when seen in the movies? And yes, the bullet striking an object makes an impressive amount of noise. THWACK!

edited typo

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[Tonto 1]

The noise depends on the calibre, barrel length, suppressor dimentions and the design of the suppressor. Very small, subsonic calibers, like .22, out of an integrally suppressed bolt action rifle are impossibly quiet, with the "click" of the striker being the dominant sound produced by the gun and the ZZZZZZZZZZZ of the bullet being the major noise at about 40 Db. Light conversation runs at about 60Db. Properly suppressed semi auto pistols (Like a 45) and sub machine guns (Like the H & K MP5 S) will sound closer to an expensive car door being closed, or a sheet tearing on full auto, the clatter of the slide or bolt will be clearly audiable, and if shooting on a hard surface, the tinkle of the falling brass take some getting used to. (You tend to want to look behind you to see what the noise is if inexperienced.) In a quiet area, it still sounds really, really loud if you're trying to be quiet.

Often, the goal of silencing is not to be completely quiet. There is almost always a great deal of ambient noise in our environment. The goal of the suppressor is to keep gunfire within the bounds of that ambient noise. Next time you're walking through a parking lot, listen to all the car doors closing. That level of noise simply doesn't register as anything threatening to us, and so we fail to respond.

Humans are intelligent, but they have an incredibly short concentration span. During the Munich Olympic massacre, athletes were killed over a three and a half hour period. The gunfire woke people, but they never knew what woke them due to the short duration. After listening for a min or two, they went back to sleep. 1000's of athletes simply thought they had a bad nights sleep until the news broke the next day. We also have a tendency to think everything is OK. A loud bang is a car backfiring, or a firework going off. We seldom think "Ah. Gunfire. I wonder where that's coming from?" Unless you're in Afganistan or Iraq. (Or downtown Johannesburg, where my GF has learned not to backlight herself when looking out the window..)

t

It's the year of the Pig.

[BetsyJ47 0]

[Never liked the idea of killing anything, even killing the rabbits as a kid.

[steve1 5]

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[I don't exceed the recommended maximum load. When developing a load, I start low, and work my way up, producing cases in batches of five, in half-grain increments. I write the charge weight on the cases with magic marker. Then I go test shoot, starting with the lowest charges, and working my way up. I watch for signs of over-pressure, and for when I find a load that has a sweet spot with the tightest groups. If I start seeing flattened primers or something,
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Actually I do the same when working up on my loads, watching for pressure signs. I've never gone over the maximum load recommended in my loading books. I strive to find the most accurate load. It's funny, but the most accurate load in my two 270's, 30/06, 300 Win., and 22-250. are right at the maximum recommended.

Probably the greatest accuracy tip that I've found so far is having the bullets almost touch the lands of the rifling. It's amazing how much tighter my groups are by doing this. This can also increase pressure though. You also have to be careful, because if they are too long they won't chamber. And if they are touching the lands this can dramatically increase pressure. On my Remington rifles the bullets are sticking out almost too far to come close to the lands. Theres just not much case gripping the bullet. I had a batch that were too long and I started having the bullet stick in the chamber when I opened the bolt.

This can ruin a hunt in a hurry if you don't have a cleaning rod to get that bullet out. I've since started using a bullet crimper on that rifles ammo, and have backed off on the distance from bullet to lands.

On one hunt I was just about to peek over a ridge to shoot at an antelope I was stalking. I openned the bolt to double check to see if the round was chambered. Luckily the barrel was pointing up because when I openned the bolt, there was the case with no bullet on it. The powder didn't spill out since it was pointing up. I closed the bolt and was still able to shoot the antelope.

I can't recall how I got my 4064 powder mixed up with my 4831. I think it was in my powder measure and not marked. That's definitely a no no. I think reloading is kind of like skydiving. It's easy to get over confident and forget about safety procedures. If you do it long enough it can bite you in the rear....Steve1

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[JohnRich 4]

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[Never liked the idea of killing anything, even killing the rabbits as a kid.

__________________________________________________

Bless You, My child.

You are the meek and shall inherit the Earth after the carnage which leaves major portions uninhabitable.

[JohnRich 4]

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the most accurate load in my two 270's, 30/06, 300 Win., and 22-250. are right at the maximum recommended.

I run into that also. Or else the best group sizes are at very near the maximum. I mostly shoot .223, .308 and .30-06, and that's the mass of my reloading. Then I have a lot of every-once-in-a-while guns in calibers like 6.5, 7.5, 7.7. I'll only load about 100 rounds at a time for those.

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Probably the greatest accuracy tip that I've found so far is having the bullets almost touch the lands of the rifling.

I need to experiment more with that. The matches I shoot have rapid fire stages, so you have to have your overall length fit into the magazine. But I also shoot 600 and 1,000 yard stages which is only one shot at a time. So I could experiment with a length that exceeds the magazine capacity, because I hand feed them one at a time anyway.

I don't have the fancy gauge for measuring that OAL that is just off the lands. But you can do the same thing by putting soot on the bullet, and pushing it in until you see the impressions of the lands on the soot. Then you back it off a few thousandths of an inch, and shoot it.

For other readers here - the idea with this is to minimize the amount of free jump the bullet has to make to get out of the case before it engages the rifling. The longer this jump is, the more inaccurate generally the bullet will be.

But you don't want the bullet jammed into the rifling, because then when the powder burns, the expanding gases meet resistance immediately, causing a pressure spike. You have to allow a little bit of bullet jump space to allow the bullet to move to relieve the pressure. It's tricky stuff, and the difference can only be a few thousandths of an inch.

[1969912 0]

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[Never liked the idea of killing anything, even killing the rabbits as a kid.

__________________________________________________

Bless You, My child.

You are the meek and shall inherit the Earth after the carnage which leaves major portions uninhabitable.

But then when all the food production and grocery stores are destroyed, he will need to kill a rabbit for food. And if he doesn't, he won't be "the meek" any more. So, he'll either starve to death or forfeit his inheritance of the earth.

What a dilemma!

[steve1 5]