mayse@cs.uiuc.edu (Chip Mayse) (11/15/89)
From: Chip Mayse <mayse@cs.uiuc.edu> In a recent posting, raymond@io.ame.arizona.edu suggested that concerning the M-16 round, "the velocity of the bullet is so high that it tumbles all the time, making keyholes on targets instead of a perfect round hole. Of course that does not help accuracy." Back when the M-16 and its 5.56 mm ammo were being developed, I remember reading that the "boattail" round was marginally stable, so that it would tumble upon impact. Does anyone out there know whether the round in fact tumbles PRIOR to impact? This seems unlikely, as it would have a very adverse effect on ballistics as well as accuracy. It certainly seems unlikely in ammunition also sold to civilians as the .223 Remington, since presumably this is a varmint cartridge. Ammo for that market generally needs max. accuracy and flatness of trajectory, with impact almost a non- issue. Perhaps the civilian versions of the .223 use different bullets, but it's hard to imagine any version's having been designed to tumble in flight. (In that case, why even bother with rifling)? [mod.note: I believe (and need not ask to be corrected if I'm wrong 8-) that this is an urban legend, of sorts. The 5.56mm ball, both the Vietnam war vintage and the newer SS-109 round, is stable in flight. If it wasn't, accuracy would be very bad. However, the stability decreases with range, as the bullet slows, so that past a few hundred meters, it begins to drop off rapidly. This stability, though, is marginal, so that the round will tumble when it strikes the target. I've seen several diagrams of 5.56mm NATO wound profiles, all show the bullet entering "normally" and tumbling once inside. (And BTW, *all* bullets seem to tumble upon impact; diagrams for 7.62 NAT0, as well as 7.62x39 and 5.45x45 Soviet, show tumbling action; but the 5.56 round does so more quickly, and also tends to fragment) Of course, this means that if the bullet strikes a leaf or twig before it reaches the target, it may tumble prematurely. If this fails to convince you, consider the numerous civilians using AR-15's for target shooting. All the holes they make in paper are round, not oblong. - Bill ]
military@cbnews.ATT.COM (William B. Thacker) (11/17/89)
From: uunet!sagpd1!jharkins (Jim Harkins) If M16 ammo tumbled in flight it wouldn't be a very accurate round. As the rifle is used in shooting matches I tend to assume it keeps its nose forward. But when it hits the target it tumbles. Or if it hits a twig, bush, or what have you it tumbles before it gets to the target (rarely hitting). But it was decided by the powers that be that being hit by a bullet that tumbled on impact was cruel and inhumane. So the original barrel twist was shortened from 1:12 to 1:8 (I think). So there's a new problem. Now when the bullet hits it fragments. So whats worse, being hit by a bullet that tumbles or by one that fragments once inside your body? I remember about 2 years ago I went to the desert with a friend who liked to reload ammo for his AR-15. He had a batch of bullets that wouldn't even hit paper at 100 yds. Nor at 50 yds. Nor at 20. At about 10 we noticed lots of little holes around the target. Turns out the bullets were tearing themselves apart as soon as they left the muzzle, he'd mistakenly bought bullets designed for the 1:12 twist and was shooting them out of a 1:8 barrel. Think about it, 1 Revolution every 8 inches, traveling about 3300 fps, is 297,000 RPM. You physics students, how much rotational energy does the jacket of this bullet have to contain, considering it's a 55 grain slug? (side note: how many grains are in an ounce/gram?). jim "Happiness is lots of little things. Green, about 2 1/2 by 6"
russ@bbx.UUCP (Russ Kepler) (11/18/89)
From: russ@bbx.UUCP (Russ Kepler) In article <11498@cbnews.ATT.COM> you write: > Think about it, >1 Revolution every 8 inches, traveling about 3300 fps, is 297,000 RPM. >You physics students, how much rotational energy does the jacket of this >bullet have to contain, considering it's a 55 grain slug? (side note: how >many grains are in an ounce/gram?). At 7000 grains to the lb thats about 15.43 grains to the gram. The 55 grain (1to8 twist usually shoots 62 grain BTW) bullet becomes 3.56 grams with a rotation rate of 297K RPM. A .223 cal slug is a nominal 5.65mm, half of which is 2.83MM spinning around and around tracing about 5280 m/s. I'll take someone with a bit more memory of physics and/or engineering to figure out the actual stress of a cylindrical lump of relatively pure lead inside a sleeve of copper. -- Russ Kepler - Basis International SNAILMAIL: 5901 Jefferson NE, Albuquerque, NM 87109 UUCP: {backboneishsite}!unmvax!bbx!russ PHONE: 505-345-5232