Naw, this was at a gunshow in AZ. And it was a full-auto capable, with the selector on the side. Well used and near abused I might add. I had no interest in picking the thing up, but it was fun to touch . . .
Tripler
And if that 1.Care, 2. See #1 was a swing at me, I don’t get it. . . 
Sleepy Weasel, yes there have been many advancements to the M-16. But since the question specified the M-16 and M-16A1, I didn’t go into the A2 or later versions. When I said I thought that the M-4 was the latest carbine version, I meant the latest military version. As you say, there are several companies who make or made versions of the M-16/AR-15.
In addition to my 1979 Colt Ar-15 “Sporter”, I also have a CAR-15 I made from an Olympic Arms lower receiver and a Bushmaster heavy-barrel upper receiver assembly (16" bbl), and a heavy-barrel (20") M-16A2 (or, since it’s semi-auto, would that be an “AR-15A2”?) made entirely from Bushmaster components.
Fortunately, I registered the receivers years ago after the first ban, even though at the time the Colt was the only one that required it. California passed a law that all “black” rifles must be registered.
Your $700 price seems a bit low. In CA (before last year’s ban) they were going for about twice that (but about half of the $3,000 pricetag mentioned). But they may be less expensive where you are.
Max, this has been bugging me for awhile. You are my new hero. Thanks. . .
Tripler
Alessan, you can see the “flat top” receiver at Bushmaster’s website: http://www.bushmaster.com/shopping/uppers/Default.htm
I’ll admit, that price was on the last day of a show, and the guy’s shop was a 4 hour drive from there with plenty of local shops to keep me from making the drive.
As for the M4, the latest Colt version I’ve seen was available in either the A2 or A3 configuration. Of course, unless you’re planning to mount a grenade launcher or that nifty baby remington, I still prefer the HB profile.
For personal use and extended carry, have you looked at the line from Professional Ordnance? Not sure how the stock would hold up if you had to whack someone with it, but for an extanded hike there are advantages to a 4 pound rifle…
http://www.professional-ordnance.com/products_ff.html
At the same sho I saw both carbine & pistol for about $900 and was sorely tempted, if only so I could be the only person around who had one.
My text defines the one-dimensional combustion wave as “propagating in one spatial direction”. Since it is just a thought experiment/example, we can do this, even though it may not be so IRL. But I can see where the confusion arises.
I lost the reply I was doing somehow…
I believe as of 1986, it is in the US illegal to trqansfer (buy/sell) any guns capable of full-auto (including selective fire) per Federal law. No new “machine gun” permits will be issued, in othwer words. I don’t know if this means if you had such a permit (pre-1986) if you could still get another one or more of them, were you so inclined.
The caseless thing that H&K was doing for the German government aparently didn’t go well, as they’re now doing field trials with something less technically ambitious.
“Controlled burn” and “uncontrolled burn” are merely poor attempts of mine at creating synonyms for “detonation” and “deflagration” for a more general audience.
Yes. The conditions that define exactly what the difference is between detonation and deflagration are hard to explain without resorting to oodles of PDE’s and a detailed ASCII art diagram of a Hugonoit curve. The basic thing to remember too is that with detonation, there is also a very large pressure increase or spike in the burned gas products relative to the unburned gas products.
I was under the impression that the 1986 law stated that no “machine guns” manufactured after that date would be sold to anyone except the military and law enforcement. This means that you could not legally modify your AR-15 into a selective-fire rifle after that date. AFAIK, you can still buy machine guns manufactured before 1986 if you live in a state that allows it. Anyone want to check with the BATF?
Tripler:
I know Max Torque already answered this, but I just want to add my $.02, since I’m in a posting-about-guns mood, and I’m gonna talk about the kind of ammo you might shoot in real life, since (I think) I recall you saying you’re military.
I don’t know what the standard NATO issue is, but Remington’s .223 V-max fires a 50 gr. bullet at 3300 fps muzzle velocity.
The equation you asked about is: e=[sup]1[/sup]/[sub]2[/sub]mv[sup]2[/sup]. the units you put in determine the units of energy you get out.
So…e=[sup]1[/sup]/[sub]2[/sub] * 50/225218 * 3300[sup]2[/sup]=1208 ft-lbs.
Or, since we’re supposed to be all metric, that’s a 5.56mm round at 1006 m/s.
So… e==[sup]1[/sup]/[sub]2[/sub] * 3.25x10[sup]-3[/sup]kg * (1006m/s)[sup]2[/sup]=1643 joules.
Since 1 j = 1.36 ft-lbs, we know I didn’t screw up the arithmetic.
Could someone explain to me what the rate of burn/explosion has to do with the speed of sound? Is this just a happy coincidence? Is the sound wave propelling the bullet?
Yup, I am military. And yup, the math works out right. . . I was looking up specs on cartridges one day (back in college), and got kinda curious to see what my .223 (which is the same as a NATO 5.56mm) would do to my Calculus book, versus my .40S&W.
True story:
So, putting my engineering skill to good use, I went out after class and shot my Calc book. The book stopped the pistol (right on page 792 as a matter of fact), but my rifle went straight through it. So, I am now trying to devise a new personal armor system based on duct tape and old college textbooks. I’d feel safe with my good 'ol Calc book in a bank heist, but not in the trenches . . .
Tripler
One of my more funnier (and happier ending) engineering stories.
Fair 'nough. As long as we’re speaking the same language.
I presume then that you’re referring to the difference in a chamber of sufficient volume to prevent a gradual build-up of pressure, or for that matter, the speed of a wave front in an unobstructed area. The addition of a gun barrel and a sufficiently heavy bullet can reduce any such wave to subsonic speeds, even if only temporarily. A perfect example would be the difference between supersonic and subsonic ammunition. As an easy example, take the 9mm Parabellum. I’ve got some nice hot loaded 90gr HP’s that would make a “crack” from the best silenced guns on the market, but load the same gun with heavy 147gr subsonics and you’re left with muzzle report alone to contend with. Take the bullet out of either cartridge, though, and the ignited powder will expel gas at supersonic speed.
No, the pressure behind the bullet propels it. If you want to get really technical, you could say the difference in pressure behind and in front of the bullet propels it, but I hate being technical. Just like in a car’s engine, a gun uses expanding gas behind a piston to harness energy. In this case, the bullet is the piston. Once out of the barrel, the bullet is no longer under propulsion, and “coasts” until something stops it. If you’re a bad shot, that usually means the ground, or a house, or a poodle… whatever.
Sethdallob,
What Sleepy said on propelling the bullet, plus, the bang you hear is the gases escaping out of the end of the barrel faster than the speed of sound, like a plane makes when you hear a sonic boom. Technically, the faster the burn, the sharper the retort (sound), depending on your medium.
Why you’d take your Calc book to a bank heist, is up to you. The other day, I shot a Calc book in my pajamas. How it got in my pajamas, I’ll never know… 
Not that these details would really put the .40 on par with the .223, but what type of bullet did you use (FMJ, JHP, JSP)? Was that a hardback or paperback? What kind of gun/barrel did you use?
As my backup for hogs, I carry a G35 with a 6.03 inch barrel for the Glock 24 dropped in for a touch of extra velocity. I’ve looked at aftermarket barrels, but the Glock’s polygonal rifling gets a tighter seal, and produces higher pressure/velocity figures than conventional rifling.
Your duct tape reminds me… I keep meaning to try something I saw in a Penn & Teller book (“How to Play with Your Food”). They refute the analysis of the Kennedy assassination film with a simple experiment using a gun, a cantaloupe, and a roll of duct tape. Allegedly, if you wrap the melon with lots of duct tape (to keep it from exploding) and set it on a post, when you shoot it, the melon jumps towards you instead of away. Their explanation is that the bullet exiting the far side takes with it a plume of melon mush in a little jet that propels the melon towards the shooter. I keep meaning to try it, but who has the time? Anyway, there are lots of lurkers around here who are “Hooked on Physics” so maybe they can post some ideas.
It’s been a long time, but I seem to recall that energy doesn’t just come from nowhere, or disappear instantly. It would then seem that the bullet would exert as much force on impact (both impacting the near side, then again the far side (assuming the resistance posed by the soft center is less relevant) as it would generate by propelling mush out the far side. Assuming a non-expanding bullet, shouldn’t the impact energy in the direction of flight be equal to the opposite direction propulsive force generated by spewing chunks of cantaloupe? Anyone? Anyone? Beuller? Beuller? Beuller?
Great story, trip! haha By any chance did you test the relative defensive values of the various sciences? Maybe a chemistry book or anatomy & physiology text would allow less penetration. <Insert ‘penetration’ pun here>
I’ve never tried it (although now I mean to), so this whole post is speculation. But I’m almost certain that what you read was more of a joke than a ballistics factoid. The whole time the bullet is traveling through the “guts” of the melon, it’s exerting force in its direction of travel. Change the equation a little bit. If somehow I were able to put my hand inside your abdominal cavity, then I yanked your intestines out at supersonic speed, would you be thrown forward, or yanked backward by the force of the exiting intestines? My guess is that you’d be yanked backwards.
Momentum needs to be conserved. That means total momentum of the bullet (because the melon is stationary, its momentum BEFORE impact needs to be the same as total (melon AND bullet together) momentum AFTER impact.
Some small amount of mass will squirt out the entry hole, and more mass will explode out of the exit hole. These won’t quite balance, but should be close. So far the melon has a very small net momentum in the direction of the bullet’s origin.
But the bullet will (obviously) be going slower on exit than it was on entry. Because of conservation of momentum, the momentum of the entry ‘jet’ + momentum of the exit ‘jet’ + momentum of the rest of the melon has to exactly equal the momentum lost by the bullet.
The entry jet should probably have slightly less mass than the exit jet, and slightly less velocity. But the mass exiting the melon at the bullet’s exit point is DRAGGED out, not blown out.
Well actually it is blown out, but it’s blown out by a traveling high pressure compression wave at the nose of the bullet. The wave is caused by the bullet pushing its way through the melon. So even though the blown out melon exerts a reactive force on the melon, that is more than counter-balanced by the initial active force of the bullet pushing the compression wave.
The only way to really figure it out would be to actually shoot one, I guess. But if it helps, I’ve shot 2-liter coke bottles filled with water. I had hoped the bottles would explode and throw water everywhere, but alas, they didn’t. They got knocked over and spilled their water (traveling in the same direction as the bullet). They didn’t even FLY away, just fell as if I had kicked them.
For the record, same thing happened to bottles filled with sand.
I once shot a partially empty, closed 5-gallon can of silver roofing sealer that happened to be in the shooting area, with an 8mm Mauser rifle. Silver junk and the lid flew about 20-30 feet in the air. Similar, though less spectacular, results occurred on the next shot; albeit without the lid.
.40SW = My Glock 23, standard stock model, with UMC 165gr FMJ.
.223 = Bushmaster AR-15 “Shorty AK Carbine”. It’s got a recoil brake on the muzzle (Works fairly well, too!) with UMC 55gr FMJ.
The book was a hardback, and I figured the “stoppage page” by the last page to be physically torn. I should note for the remaining 100 pages or so, the ink from those pages has been smooshed so hard, it imprints itself on the adjoining page.
I did get a little creative a few weeks later, and started messing around with old dinner plates I had. I found that if you stack two ceramic dinner plates in front of your book (and duct tape 'em together), the ceramic will mushroom the round and really reduce the penetration into the book. This system stopped the .40 at about page 158 and the .223 at about 750 (IIRC).
Further testing would have occurred, but I ran out of books to shoot. . .
Tripler
You really should give this a try sometime. It’s cleansing and educational!
[QUOTE]
*Originally posted by Johnny L.A. *
**
Now, I did also go out with a friend once, and we took along the near-empty can of clear spray laquer. I set it down on the ground, walked about 15 yards away, lined up my rifle and fired. I had my friend watch it . . .
So, I go bang and when the flash drops, the can is gone. So I perk up and start looking where I had just shot (figuring I knocked it over). Just as I had said “Where the hell is i. . .” I hear this ‘clump’ and look back. My bud is pointing to a spot 45 feet behind us, which we walk over to to find the can. Apparently, I had shot the thing perfectly on center, just 1/4 inch from the bottom. The “exit wound” launched the damn thing (he says) “fifty feet up and over us like a rocket” landing behind us. It was the only time I ever had a dead target try to flank me. . .
Aah, the benefits of college in Arizona. . .
Tripler
Another happy-ending engineering story. Don’t ask me about 1/4 Watt Caps on 6 Watt transformers though . . .