Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!samsung!brutus.cs.uiuc.edu!psuvax1!rutgers!att!cbnews!military From: mayse@cs.uiuc.edu (Chip Mayse) Newsgroups: sci.military Subject: M16 Ammo Message-ID: <11436@cbnews.ATT.COM> Date: 14 Nov 89 23:27:17 GMT Sender: military@cbnews.ATT.COM Lines: 38 Approved: military@att.att.com From: Chip Mayse 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 ]